Arthur G. Fett-Neto
Zooming In and Out: Molecular and Whole Plant Approaches to Understand Hard-To-Root Eucalyptus Cuttings
The sessile nature of plants and the strong link between structure and function contribute to the complex multilayered character of plant physiological processes. To get a grasp on the mechanisms that control developmental responses, integrated approaches, ranging from whole plant to tissue /cell specific analyses, from counting organs to gene transcripts, from metabolite quantitation in tissue extracts to immunolocalization, are of paramount relevance. To illustrate these assumptions, we will examine the search for the underlying mechanisms determining adventitious rooting (AR) in a hard-to-root eucalypt. Knowing the physiological mechanisms underlying limited AR will help to pinpoint bottlenecks, eventually improving clonal propagation. Eucalyptus globulus and its hybrids are of great interest in the paper industry, but are often recalcitrant to AR. Exogenous auxin reverses the AR recalcitrant phenotype in E. globulus. Auxin accumulation and origin of adventitious roots co-localize to the vascular cambium. Cambium-specific gene expression analyses indicate that TOPLESS and IAA12, auxin signaling repressors, and ARR1, involved in cytokinin signaling pathway, act as negative regulators of adventitious rooting. Auxin exposure diminishes expression of these genes. Comparatively, in the easy-to-root E. grandis, expression of AR inhibiting genes was much lower, whereas basal endogenous auxin concentration was higher. The same set of genes was associated with age-dependent loss of AR capacity in E. globulus, which also correlated with decreased expression of auxin biosynthesis-related TAA1 and auxin receptor TIR1. Endogenous auxin content decreased and peroxidase activity (involved in auxin degradation) increased with loss of AR capacity. Auxin action repressors and endogenous auxin content appear as key components in a working model of AR recalcitrance in E. globulus, being potential targets to modulate this developmental process. Clearly, diverse and complementary approaches hold the key to dissect developmental events.
Augusto C. Franco
The interplay of Plant Form and Function in the Savannas of Central Brazil
The performance of any plant and its ability to successfully respond to environmental change depend to a large extent on its plasticity in regulating the energy metabolism and the efficient remobilization of carbohydrate and minerals from storage compartments in different parts of the plant. This is ultimately related to the structure and functioning of the leaves, stem characteristics related to transport of water and nutrients and the efficiency of the root system in the uptake of water and nutrients. Although there is a great variation in the structure and physiology of these organs, environmental and development constraints and selective pressures constrain and delimit the spectrum of variation, leading to convergence and the occurrence of well-defined syndromes, resulting from the correlation between several attributes, whose phenotypic expression depends on the regulation and modulation of metabolic processes. A variety of plant communities, differing in floristic structure and composition, can be found in the savannas of Central Brazil. Interactions between the disturbance regime, where fire plays a predominant role, and the availability of resources (water and nutrients) determine the distribution of the various plant communities, of contrasting structure and composition, which coexist in the region. The environmental and vegetation heterogeneity is accentuated by the territorial extension of the biome, variations in topography and soil types. This great diversity of species from different evolutionary lineages and the strong environmental heterogeneity provides an excellent opportunity for studies that aim at understanding the evolution of form and function, and that seek to decipher adaptive and evolutionary limitations in plants. Here I focus on studies that integrate trait syndromes and plant morphology, because they better reflect the coordinated evolution of structure and function of the whole plant. Different plant morphologies are generally categorized into a diversity of growth forms that represent the overall physical form and external structure taken by the plant. Despite the high species diversity and the independent evolutionary trajectory of individual species, I show that growth forms can be associated to particular leaf trait combinations in the savannas of Central Brazil, suggesting evolutionary constraints on leaf function for morphologically similar species. I also present evidence of partitioning of soil water resources by different growth forms and how this affects plant water balance. At the ecosystem level, I use results of manipulative experiments of nutrient availability to show how changes in resource availability differently affect the woody and the herbaceous layer. Lastly, I focus on woody plants to develop a trait-based approach providing new insights on plant adaptations to withstand drought, fire and nutrient-poor soils in tropical regions worldwide.
Anaerobic Metabolism - a Tool for Preserving the Quality of Apples
To prolong the storage period of apple growers use controlled atmosphere (CA), in which the oxygen concentration of the room is reduced down to 1.0% or higher, depending on the cultivar. A little more than a decade the technology of Dynamic controlled atmosphere (DCA) was introduce in the market, which use an oxygen level of 0.4%. In this technique, which has benefits compared to conventional CA, the stress level of the apple is monitored by the determination of the fluorescence of chlorophylls in the skin of the fruit. More recently, work carried out in the Netherlands and in the Postharvest Research Center of the UFSM found that it is possible to reduce even more the level of oxygen in the storage room for additional benefits in conservation of the quality of apples. In this case, the minimum oxygen level tolerated by fruit is monitored through the determination of respiratory quotient (RQ), which is the ratio of CO2 production and the O2 uptake in a given time period (12 to 24h). When the fruit is not in low oxygen stress the RQ is near 1.0. With a further reduction of the O2, the anaerobic metabolism, in which are released more molecules of CO2 than the O2 molecules consumed, resulting in a RQ above 1.0. In the literature the anaerobic metabolism in fruit has always been considered as a deleterious and unwanted event, because it would lead to the accumulation of ethanol and acetaldehyde in the cells, which would cause its death. However, in our work with 'Gala' and 'Fuji' apples we found that anaerobic metabolism, called by many as fermentation, occurring in small proportions is beneficial to the conservation of the fruit, keeping a greater firmness and reducing the occurrence of physiological disorders, as the mealiness, internal breakdown and scald. It was noted that the ethanol produced by anaerobic respiration or applied externally, reduces respiration and ethylene production of the fruit, slowing its ripening, moreover, ethanol is used for fruit as a precursor of esters, which are the main components of the aroma of apple. Ethanol can react with an organic acid to form an ethyl ester or can be transformed to acetic acid, which can combine with an alcohol, usually with 2 to 8 carbons, forming also an esters. The reduction of the O2 to 0.4% in DCA monitored by chlorophyll fluorescence drastically reduces volatile compounds production, but a further reduction of the O2 at a concentration close to 0.2%, obtained by the RQ technique, increased two to three folds the volatile compounds production, especially esters, alcohols and aldehydes. The accumulation of ethanol is converted into acetyl CoA to combine with alcohols of 4, 6 and 8 carbons from the degradation of fatty acids by beta oxidation. Esters are also formed by the combination of acetyl CoA with fatty acids with odd number of carbons from the degradation of amino acids. The accumulation of ethanol hinders the degradation of fatty acids causing a greater availability of fatty acids with 4 to 8 carbons, which are used in the formation of important esters that contribute to the aroma. The determination of the stress through the quantification of RQ showed that at the beginning of the period of storage, apples do not tolerate low levels of the O2. With the evolution of time (30 to 60 days), the fruit metabolism adapts to low oxygen conditions requiring only 0.1% of the O2 or less to keep a RQ 1.3, that generally is the optimal level of stress to the apple cultivars evaluated. The DCA-RQ with extremely low concentrations of the O2 even allows an increase of 1°C or more of the temperature of the storage room, with a great saving of energy consumption. In addition, the DCA-RQ technology could be a substitute for the application of 1-MCP, which is an inhibitor of ethylene action, widely used in the conservation of apples what would bring a great financial economics.
Metabolomics: a Powerful Tool for Plant Physiology Studies
Metabolomics, which represents the chemical composition in a cell, is a powerful tool in deciphering metabolism and bridging the phenotype–genotype. Despite significant advancement in analytic tools, complete coverage of the metabolome will always be constrained by polarity, stability, dynamic range and biological properties of metabolites. Therefore, the optimal choice for an analytic technology will largely depend on the goal of each study and is usually a compromise of selectivity and speed. As plant growth is closely linked to central metabolism network, gas chromatography coupled to mass spectrometry (GC-MS) technology is a gold standard for a comprehensive coverage of primary metabolism pathways (e.g. organic and amino acids, sugars, sugar alcohols, phosphorylated intermediates and lipophilic compounds). This mini-course will provide a broad overview of key issues in metabolomics analysis- from experimental design to data interpretation and it will encompass theoretical lectures and discussions in crucial topics. Examples of the potential of metabolite profiles to predict plant performance as well as in plant molecular physiology will be presented.
Carlos Henrique B. A. Prado
Teaching Plant Physiology
After a significant accumulation of knowledge along the twentieth century, the interest in plant physiology in Brazil has been decreasing. There are several explanations, including the competition with other areas considered "naturally" more attractive. Today there are arguments and means to change, via education, this situation. In this forum, I will discuss innovative approaches for teaching plant physiology that consider plants’ role in sustainability, communication, and their interaction with terrestrial spheres and heliosphere. Currently, some of the most relevant issues for humankind are sustainability and communication. Who does the popular 3 Rs (reuse, recycling, and reduction) better than plants? The network communication with various actors characterizes our society today. It is what plants do with other plants, animals, fungi and bacteria through the subterranean, aerial or aquatic portions. Such themes strongly attract students and are part of ordinary processes of plant functioning. Plants working as a biotic pump are responsible for an important portion of the continental rains. Moreover, their roots are significant points of articulation of the hydrosphere, lithosphere, and biosphere. Photosynthesis generating a single terrestrial sphere, the biosphere, using an extraterrestrial sphere, the heliosphere, imposes constant changes on the planetary scale. Using this approach, it is possible to foster empathy and sympathy among students towards plants. Therefore, the students’ ability to put themselves in the position (empathy) and to be attracted to the shape and functioning (sympathy) of a plant can be improved. Botany and erudition meet when they increase the repertoire of knowledge and give the students the opportunity to recognize and understand themselves in the vegetation.
Carlos L. Ballaré
Universidad de Buenos Aires, Argentina
Light Signaling, Competition and Defense Responses in Plants
Light signals, perceived through informational photoreceptors, are used by plants to detect and respond to the proximity of competitors. Low red:far-ratios (R:FR) in the canopy light reduce the proportion of phytochrome B (phyB) molecules that are in the active form, and promote the synthesis of growth-related hormones, including auxin and gibberellins, which in turn stimulate shoot elongation and other shade-avoidance responses. At the same time, recent research demonstrates that phyB is an important modulator of the two principal hormonal pathways that regulate plant immunity against herbivores and pathogens, i.e. the jasmonic-acid (JA) and the salicylic-acid pathways (SA). Low R:FR ratios down-regulate JA- and SA-induced defense responses. This down-regulation is thought to help the plant to efficiently redirect resources from defense to rapid growth under conditions of intense competition. In this presentation, I will discuss recent advances in the understanding of the mechanisms that link phyB with JA signaling, and explore the consequences for direct and indirect defenses. Unveiling the molecular links between photoreceptors and the regulators of plant immunity is important to generate a mechanistic framework to understand how plants deal with resource allocation trade-offs under natural conditions. This mechanistic understanding can be very useful to guide breeding programs aimed at increasing plant resistance to pests and pathogens in cultivated species.
Seoul National University, Korea
Stem-piped Light Activates Phytochrome B to Trigger Light Responses in Arabidopsis Roots
Light regulates virtually all aspects of plant growth and developmental processes throughout plant life. A group of photoreceptors perceives a wide range of light wavelengths, such as ultra-violet (UV), blue (B), red (R), and far-red (FR), to monitor the plant’s surrounding environment. The roles of photoreceptors and associated signaling mechanisms have been extensively investigated mostly in the photomorphogenic processes of aerial plant parts. Accumulating evidence in recent years strongly support that light also influences root growth and development. However, how aboveground light influences the root system has not been systematically explored. Here, we show that light is efficiently conducted through the stems to the roots, where photoactivated phytochrome B (phyB) triggers gene induction and protein accumulation of the positive photomorphogenic regulator ELONGATED HYPOCOTYL 5 (HY5). Accordingly, Arabidopsis plants that are defective specifically in root HY5 exhibited alterations in root growth and gravitropism. These findings demonstrate that the underground roots directly sense stem-piped light to monitor the aboveground light environment during plant environmental adaptation. Our data would also provide molecular insights into plant intellectual behaviors and, in particular, clues as to a long-sought hypothesis ‘Do plant roots harbor brain or brain-like tissues?’ proposed by Charles Darwin.
Drought Tolerance: which Genes or Alleles for which Drought Scenarios?
Current and future climatic conditions are characterized by large year-to-year and site-to-site variabilities. Drought tolerance results from an optimization between processes, traits and alleles leading to either minimize the risk of crop failure or to increase crop production. Evolution has tended to favour conservative processes (short crop cycle, low transpiration and leaf area, high investment in roots), positive in severe drought scenarios, whereas yield in milder water deficits is associated with opposite traits. Hence, a given genomic region affects plant performance in at most half of the fields in networks of dry experiments, and the allele associated with best performance often changes between sites. We propose that this is the general case, so one does not aim at identifying generic genes and alleles of drought tolerance, but to identify which gene and alleles are favourable in which drought scenarios. A strategy is proposed consisting in (i) identification of most frequent scenarios by clustering environmental data characterizing the target population of environment (typically 50 sites x 50 years). (ii) Performing genetic analysis in a network of field and for identifying genomic regions associated with crop performance (iii) Classifying experiments into the identified clusters of scenarios based on time course of environmental conditions, thereby identifying which alleles controlling which traits are favourable in which scenarios. (iv) estimating the genetic control of essential variables such as stomatal conductance or sensitivity of growth to water deficit from high throughput experiments in a phenotyping platform (v) Based on the latter parameters, modelling the effect of combinations of alleles in the scenarios identified in step i. As a whole, the combination of field and platform steps results in a dataset allowing one to identify genomic regions associated with tolerance in specific scenarios of heat and drought, and with traits associated to these genomic regions.
Francisco de Almeida Lobo
Theoretical Aspects on Plant Gas Exchange with Emphasis on Water Use Efficiency
Plant gas exchange measurements are useful because they allow for the analysis of how operates CO2 assimilation and water vapor loss via photosynthesis and transpiration, respectively, under specific conditions of the most immediate factors affecting photosynthesis such as light, temperature, relative humidity and atmospheric CO2 concentration. Stomatal conductance controls this leaf-atmosphere gas exchange, and precisely for this reason, it must be well understood. As such, it is necessary to take into account not only the physical aspect related to the molecular diffusion coefficients of CO2 and water vapor, which depend only on the nature of these molecules, but also the physiological aspects related to the stomatal frequency and the regulation of stomatal dimensions, specifically the pore size. There are many variables that are obtained from gas exchange measurements, such as the instantaneous water use efficiency and intrinsic water use efficiency, whose utility, from an ecophysiological point of view, depends on the correct interpretation of the set of variables which compose them, and considering the physical conditions of the environment in which the measurements were performed. The aim of this short-course is to reinforce the biophysical concepts of the gas exchange variables and to clarify how these variables are obtained instrumentally or by algebraic estimates, in order to correctly interpret them.
Agricultural University of Athens, Greece
Alarm Photosynthesis: a “Crystal Clear” Case of Drought Tolerance
The occurrence of calcium oxalate crystals in plant tissues was an enigma for plant scientists for a long time and our knowledge on their formation and possible roles in plant function remained limited. Recently, we found that leaf crystals function as dynamic carbon pools that collect non-atmospheric carbon, mainly during the night. During the day, crystal degradation provides oxalate which is converted to CO2 by the enzyme oxalate oxidase when stomata remain totally or partially closed (e.g. under drought conditions) and the risk of CO2 starvation within mesophyll is increased. This biochemical appendance, named alarm photosynthesis, provides a number of adaptive advantages that explain the vast presence of calcium oxalate crystals in plants and especially in xerophytes.
Gustavo M. Souza
Toward a Systemic Plant Physiology
In this lecture I will bring a critical reflection on the epistemological foundations of the science of plant physiology, discussing the limits of the reductionist view of the modern science. Then, I will present the epistemological and theoretical principles of a systemic science (or systemic paradigm), based on General Systems Theory and their ramifications into the Complex Systems Theory and Self-Organization. As a consequence, a new perspective of plants as self-organizing complex systems will be presented, endowed with cognitive properties. Thus, the basis for the proposal of a systemic approach for plant physiology, with its implications in science itself, scientific education, economy, and the society will be considered.
University of Western Australia, Australia
Plant Mineral Nutrition in Biodiversity Hotspots
Australia is a global biodiversity hotspot, where the greatest plant diversity is found on the most severely phosphorus-impoverished soils in kwongkan (low heath on sandplains). A similar situation occurs in campos rupestres in Brazil. Mycorrhizas are symbiotic associations between plants and fungi that enhance plant phosphorus acquisition. Paradoxically, non-mycorrhizal plant families (e.g., Proteaceae) feature most prominently on the poorest soils in Australia, and these families are uncommon on soils containing more phosphorus. In campos rupestres, non-mycorrhizal species are also remarkably common. Almost all Proteaceae produce carboxylate-releasing cluster roots, which are capable of mobilising scarcely available phosphorus and micronutrients, including manganese. They effectively ‘mine’ these nutrients, as opposed to ‘scavenging’ them from the soil solution further away from the root surface, as mycorrhizas do. In addition to efficient acquisition of phosphorus from soil, south-western Australian Proteaceae species also use the acquired phosphorus very efficiently in photosynthesis. They also show a tremendous capacity to remobilise phosphorus from senescing leaves and contain a large amount of phosphorus in their seeds. The traits referred to here help explain the ecological success of non-mycorrhizal species on severely phosphorus-impoverished soils in south-western Australia. These same traits may also have allowed non-mycorrhizal families to diversify in these severely nutrient-impoverished environments. A very exciting question that remains to be explored further is why species with a superior phosphorus-acquisition strategy coexist with ones that are less effective at acquiring soil phosphorus. We have some answers, involving both facilitation and pathogen susceptibility, but future research will explore this in greater detail.
Harry Westfahl Jr
Brazilian Synchrotron Light Laboratory, Brazil
The Potentialities of Sirius, the New Brazilian Synchrotron Light Source, for Plant Physiology Research
The application of synchrotron radiation in a large variety of fields, from biology to microelectronics, has increased steadily worldwide. To a large extent this is a result of the availability of much brighter synchrotron light sources, which provided new experimental techniques to investigate different aspects of matter, from atomic organization to electronic structure. Recently, new developments in accelerator technology are paving the way for even brighter sources, which are being named fourth-generation light sources. Sirius, the future new Brazilian synchrotron light source, is one of the first two such machines in construction in the world. Its first experiments are expected by 2019 and it is being planned to be a state of the art light source, providing cutting edge research tools that are nonexistent today in Brazil, like 3D chemical mapping with nanometer resolution. The Sirius project is designed and executed by the Brazilian Synchrotron Light Laboratory -- LNLS, which was also responsible for the construction of the current second generation Brazilian light source, UVX, the first synchrotron in the southern hemisphere, and still the only one in Latin America. In this talk an overview of the main characteristics and potentialities with advanced techniques for studying plant physiology will be provided as well as the status of the project.
University of the Balearic Islands, Spain
Evolution of Rubisco, Ecophysiological Consequences of Natural Variation and Opportunities to Boost Crop Productivity
The importance of Rubisco would be difficult to exaggerate. It provides the unique quantitatively significant conversion point from inorganic into organic carbon, sustaining the vast majority of food chains and life in the Biosphere. Paradoxical to its prodigious task, Rubisco hosts a number of catalytic imperfections, which limit the rate of photosynthetic CO2 fixation and plant growth capacity. The present talk will first concentrate on the ecophysiological causes of the existing natural variation in Rubisco constitutive traits among distant phylogenetic groups of photosynthetic organisms. Within higher plants, targeted examples, based on closely related group of plants, will be provided to underpin the molecular determinants for the reported variation. At the ecological level, evidence of high selection pressure on Rubisco along gradients of CO2 and temperature suggests that exploration of species adapted to extreme environments or possessing innovative adaptations will reveal the existence of Rubisco of unusual pedigree out of the reported bounds. Rubisco performance in the most economically important crops worldwide will be presented and related to models of leaf photosynthesis to assess the limitations imposed on crop productivity under current and future environments. In the context of climate change, the catalytic response of Rubisco to increasing temperature and CO2 will have direct repercussions for the photosynthetic performance of autotrophic organisms, and indirectly for the productivity of the main ecosystems. The existence of significant variation in the affinity for CO2 and in the thermal dependencies of Rubisco among the diverse photosynthetic organisms push to suggest that not all the Rubiscos (and hosting species) will become equally affected. Finally, how naturally improved versions represent an exceptional opportunity to supercharge photosynthesis and preadapt crops to oncoming changes by novel bioengineering strategies of crops will be reviewed and linked to specific methodological approaches.
Joaquim Albenísio G. Silveira
Why Is so Hard to Reveal Plant Scientists in Brazil?
In this presentation I will discuss a critical subject for plant physiology development in Brazil and much probably in the worldwide. This problem is not inherent to plant science but, in contrast, it is broadly disseminated in all other science areas. This question involves complex components encompassing since psychological, sociological and familiar aspects during children education until formal education. Commonly, the Brazilian teachers of basic sciences at fundamental level and of other disciplines such as chemistry, physics, biology and mathematics, are not scientists. Altogether, this frame generates discouraged and poorly prepared students to develop plant physiology high studies. Thus, to reveal good Brazilian plant scientists in the future are needed to adopt diverse coordinated strategies involving several actors of the society.
León A. Bravo
Universidade de la Frontera, Chile
The Impact of Regional Warming on the Unique Vascular Flora of Antarctica: An Overview of Antarctic Plant Ecophysiology
Deschampsia antarctica Desv. and Colobanthus quitensis Kunth Bartl. are the only two plant species that have naturally colonized the Maritime Antarctica. What special features do these two species have to be the only vascular plants widespread in this harsh environment, has been an enigmatic question for scientists. These plant have developed different strategies to deal with low temperature associated stresses. For instance, D. antarctica is more freezing tolerant than C. quitensis exhibiting high capacity to withstand freezing temperatures way below the ice nucleation temperatures, C. quitensis maintains supercooling capacity but exhibited damage at temperatures close to its ice nucleation temperature (tolerance vs avoidance of freezing). This is related with interspecific differences associated to accumulation of different cryoprotectants and also with different mechanism able to protect functional integrity of these plant from damaging reactive oxygen species and finally, their differential capability to produce cryoprotective and antifreeze proteins. But it is not only freezing tolerance which account for their survival and population expansion in Antarctica, there are also morphological and reproductive traits of these species that play an important role. For instance, prostrated habit of both plants leaf size and morphology, plus some particular attributes such as special salt glands in D. antarctica and vivipary observed in C. quitensis are also remarkable. But all this cold adaptation is now challenged by the regional warming experienced by The Antarctic Peninsula in the last century. Many questions have been raised about plant performance and their fate in this new scenario. Results from an in situ warming experiment will be discussed and provide further insights.
How to Estimate Vulnerability to Embolism by the Pneumatic Method
There is a high quantity of air even in functional xylem conduits (tracheyds and vessels). Embolism formation interrupts the water transport and affects the plant growth and survival. To avoid embolism, plants can close stomata and increase xylem water potential, but with the cost of reduced photosynthetic rate. The mortality of trees under drought has been explained by vulnerability to embolism formation. This vulnerability can be estimated by measuring the quantity of air formed, related to xylem water potential, during the dehydration of a branch. The conventional methods can be laborious and there are several artefacts described in the literature, making it difficult to obtain reliable vulnerability curves. In this short-course, we will detail theoretical and practical aspects of different methods, highlighting the advantages of the pneumatic method (PM). In the PM, the loss of xylem conductivity is estimated by extracting a portion of air from branches, using a simple apparatus constructed with a vacuum-meter and connections. Each measurement takes about two minutes, allowing the estimation of simultaneous vulnerability curves from different branches, using only one apparatus. The PM has allowed an increase in the number of species studied around the world, mainly from tropical forests, helping the understanding of the physiological strategies to embolism resistance.
Chlorophyll Metabolism and Senescence Engineering for Yield and Nutritional Quality Improvement
Leaf senescence initiates when photosynthetic potential riches the maximum capacity and during its progression photochemical activity decreases due to the degradation of the photosynthetic machinery and nutrients are translocated to non-senescent plant organs. Several evidences indicate that the delay of senescence maintaining the production of photosynthates for longer periods results in yield increment becoming an important agronomical trait. Chlorophyll (Chl) degradation is also an interesting process for metabolic engineering aiming nutritional quality improvement. Chlorophyll dephytylation produces phytol, which is a precursor of tocopherols, compounds with vitamin E activity. These potent antioxidants have shown to protect pigments, proteins and fatty acids involved in the photosynthetic apparatus from the reactive oxygen species (ROS) produced during photosynthesis. Regarding human health, the vitamin E prevents cardiovascular diseases, cancer of mammary glands and oxidative stress caused by nicotine. Most of the studies approaching senescence and chlorophyll degradation use the model species Arabidopsis thaliana or grasses; however, few reports describe these processes in freshly fruit producing plants. In this sense, Solanum lycopersicum is an excellent model due to the nutritional and economic importance of this species. The characterization and manipulation of chlorophyll dephtytylases, phytol recycling and senescence-related genes have revealed the link of Chl metabolism with important nutraceutical compounds (i.e. carotenoids and tocopherols) and their impact on yield. The combined results impose another level of complexity to isoprenoid-derived compound regulatory network, unveiling new strategies for source-sink balance and nutritional quality engineering.
Signaling and Modulation of Secondary Metabolism by Nitric Oxide During Seed Germination and Root Hair Formation
NO is a gaseous free radical involved in the regulation of various plant developmental process. Treatment with exogenous NO enhanced phenolic and flavonoid contents in plant cells and microorganisms. Our group investigated if exogenous NO is able to modulate the production of secondary metabolites during seed exudation and root hair formation by using native and model species. Seeds of Sesbania virgata, a tropical invasive species that exudates antifungal and phytotoxic compounds, such as sesbanimide A and (+)-catechin, were used to investigated the effect of gaseous NO on germination, early development, exudation of phytotoxic compounds and activation of antioxidant defenses. NO fumigation led to a reduction in total phenols and tannins in the seed exudates of S. virgata, with catechin being identified as the main reduced compound. This reduction was show to result from the NO scavenging activity of catechin. Our results suggest that the ability of catechin to scavenge NO could contribute to maintain NO levels under optimal conditions to stimulate antioxidant enzymatic defenses of S. virgata and maintain ROS homeostasis, without affecting the phytotoxic activity of their exudates. Using mutants of Arabidopsis thaliana with altered root hair phenotypes, we also investigated the involvement of S-nitrosoglutathione (GSNO), the primary NO source, on gene expression in roots induced to form hairs. Besides modulating the expression of a large number of genes related to cell wall biosynthesis, GSNO also regulated the expression of many genes related to root secondary metabolism. The flavonoid branch of the phenylpropanoid biosynthetic pathway was the main affected route. Among the most affected genes are included Laccases, Transparent Testa (TTs) and genes involved in ligninin biosynthesis, as PAL, F5H, CAD, 4CL and CcoAOMT. Both experimental systems demonstrate a central regulatory role of nitric oxide on secondary plant metabolism.
Marcelo Carnier Dornelas
Axillary Bud Identity and Phase Transitions in Passiflora spp
An important issue in plant biology is how morphological novelties are produced during evolution. The genus Passiflora includes plants that display complex structures whose origins have not been elucidated yet. Among such structures there are the floral corona filaments and the tendrils in the axils of the leaves, next to a flower bud. Juvenile Passiflora plants do not have tendrils. On the other hand, adult plants of Passiflora constantly produce tendrils associated to flower buds. The axillary meristem is subdivided into two domes, one that forms the tendril and another one that forms the flower meristem. An accessory axillary meristem is formed in between the tendril-flower complex and the stem, which corresponds to the axillary vegetative bud. The ontogeny and the arrangement of these structures have led some authors to consider the Passiflora tendril as part of the primary axis of a reduced inflorescence. Nonetheless, the molecular mechanisms that define these structures of common origin but with different identities are not clear. Our hypothesis is that conserved physiological and molecular mechanisms that modulate meristematic activity, either regulating determinate versus indeterminate growth or de novo meristem organization might be playing a role on the origin of both tendrils and corona filaments. Using tools appropriate to the study of ontogenesis and development, associated to transcriptome and gene expression analysis, we aim to unravel the cellular and molecular mechanisms underlying the identity and the ontogenesis of such elusive organs that represent evolutionary novelties in plants.
Marcio Rodrigues Lambais
Microbiomes of tree species of the Atlantic Forest: diversity and functionality
For the understanding of phytobiomes, i.e. all organisms (microorganisms, insects, nematodes and plants, among others) that live in the interior, on the surfaces or in the area of influence of the plants, the surrounding environment, and the multiple biotic interactions and interactions between organisms and environment that affect plant growth, the study of plant microbiomes is essential. Microbiome is defined as the set of microorganisms (bacteria, archaea, fungi, protozoa and viruses) and their genomes in a given environment. In general, the plant microbiome may play important roles in regulating host physiology and molecular communication between plants and between plants and other organisms, contributing to their adaptation to the environment. The plant microbiome includes the microbial communities on the plant surfaces (phyllosphere and dermosphere, for example), inside the plant (endophytic) and in the rhizosphere. In previous studies, we estimated that the plant microbiome of the Atlantic Forest (phyllosphere, dermosphere and rhizosphere), not including the endophytes, may harbor from 72 to 1,400 million bacterial species. In another study, using 16S rRNA gene amplicons, we have determined that the structures of the bacterial communities living in the phyllosphere, dermosphere and rhizosphere of different tree species depend on the plant taxon, suggesting the existence of selection mechanisms that may reflect evolutionary conserved genetic traits. Among the microorganisms that make up the plant microbiome, those living in the phyllosphere are of great interest for their possible roles in the protection of plants against pathogens and pests, besides their involvement in nutrient cycling and promotion of plant growth. Evaluating the metaproteome of the microorganisms in phyllosphere of different tree species in the Atlantic Forest, we have observed that, despite the different taxonomic composition, most functional groups of proteins were common to several phyllospheres, suggesting that the bacterial populations of different phyllospheres share a set of functional proteins necessary for their adaptation and survival in this environment. Among the metabolic processes that occur in the phyllosphere of different plant species, biological nitrogen fixation (BNF) is one of the most important. In the Atlantic Forest, the BNF associated to the phyllosphere of several tree species may be as high as the BNF associated to the litter, suggesting that the contribution of the BNF in the phyllosphere to the N input may higher than other contributions, changing paradigms of N cycling in tropical forests.
Facing Aluminum and Other Oxidative Stresses in Rice
In my lab we are studying the molecular mechanisms involved in plant development and responses to environmental stresses. To develop our research we are combining genetic, molecular biology and genomic strategies, applied to plant models such as rice and Arabidopsis. The ASR (ABA, Stress and Ripening) genes are induced by stress and abscisic acid (ABA). Plants overexpressing ASR have shown the potential use of these genes to increase the tolerance of plants against abiotic stresses. In rice, in silico analysis revealed the presence of six copies of the ASR genes, dispersed on different chromosomes. We are applying strategies of reverse genetics and proteomic to understand the function of ASR genes in the defense of plants against stress by aluminum. The protection of the plant can also be given through the maintenance of low levels of Reactive Oxygen Species (ROS) by increased expression of antioxidant enzymes. Moreover, since H2O2 is also a molecular signaling of plant defense responses, transcriptome analysis of plants silenced in different genes related to redox homeostasis may reveal a complex network of gene expression regulation controlled by H2O2.
Paul C. Struik
Wageningen University & Research, The Netherlands
Spatial aspects of leaf and canopy photosynthesis in C3 and C4 plants
To ensure future food security and adequate energy supply for a rapidly growing and increasingly demanding population living on a planet of which the climate is rapidly becoming less conducive to agriculture, the productivity of agricultural crops will have to increase, at rates higher than currently possible. Therefore, science needs to improve the photosynthetic competence of crop plants. The energy budgets and biochemistry of C3 and C4 photosynthesis are relatively well studied. However, the spatial aspects of gas exchange, light propagation and capacity of biochemical processes at the level of the individual leaf and the quantitative scaling up of aspects of leaf photosynthesis to the canopy level are relatively unknown. In collaboration with the University of Leuven, our Centre for Crop Systems Analysis combined actual leaf 3D-microstructure (based on synchrotron radiation X-ray laminography) with spatially explicit models of CO2 diffusion, 3D light propagation, and biochemistry, and with leaf-level models of photosynthesis. This was done for the C3 crop tomato and the C4 crop maize. We also created 1D, 2D and 3D reaction-diffusion models based on artificial leaf microstructures which are less computationally demanding. We evaluated the models based on data obtained from gas exchange measurements and leaf optical properties. We used these models to assess whether genetic variation in leaf anatomy affects photosynthesis (for tomato) and to evaluate how important nitrogen supply is on bundle-sheath conductance (for maize). Moreover, we used the models to assess whether distribution of photosynthetic capacity, chloroplast and mitochondrion position, activity of carbonic anhydrase, re-assimilation of (photo)respired CO2 and anatomical constraints to the CO2 concentrating mechanism have an impact on photosynthesis. We also investigated how important lateral gas exchange within a leaf is for homobaric and heterobaric leaves. Using the crop growth model GECROS we illustrated for rice the effects of genetic variation and genetic engineering of biochemical components of leaf-level photosynthesis on canopy photosynthesis and biomass production. To produce more efficient crops we need to combine improved CO2 concentrating mechanisms, photosynthetic capacity, and quantum efficiency simultaneously.
Rogério F. Carvalho
The Light in the Plant's Life: a Focus on Photoreceptors
Although many organisms can avoid environmental adversities, such as move on, plants are sessile and thus they cope with multiple forms of stress in the same time. Therefore, plants are able to trigger compensatory mechanisms to growth under stress conditions. Among the key signals that control plant development, light is the most important environmental cue. To perceive the light and trigger many photomorphogenic responses, plants have evolved a remarkably sophisticated system of light signal transduction pathways initiated by photoreceptors, which are characterized by the wavelengths of light they absorb. Thus, the aim of the mini-course is to talk about the most characterized plant photoreceptors and their roles on plant growth, as well as on ecological dynamics and important trait for breeders due to evidence of photomorphogenic control of a wide range of responses of high horticultural value.
Stanisław M. Karpiński
Warsaw University of Life Sciences, Poland
PsbS and Transthylakoid pH-Gradient Regulates Cellular Light Memory of Acclimation, Cell Death and Crosstalk of UV...
PsbS is a key protein involved in regulation of transtylakoid pH-gradient-dependent non-photochemical quenching (NPQ) of absorbed energy. Recent studies by Kromdijk et al. 2016 (Science) show that appropriate transgenic manipulation of gene expression for PsbS and VAZ cycle enzymes lead to increased plant biomass production in variable light/field condition. However, PsbS function has been exclusively studied in light acclimatory responses. In our recent studies we reported that rapid electrical signals in response to a local heat stimuli regulate systemic changes in NPQ and quantum efficiency of photosystem II (Białasek et al., 2017, PCP). Here we demonstrate that PsbS regulates cellular light memory (also in Szechyńska-Hebda et al., 2010, TPC), cell death and crosstalk of UV-C and excess light stress. We observed enhanced tolerance of wild type (WT) low light acclimated plants to UV-C stress episode expressed by lower induction of cell death when plants were pre-treated with red or blue excess light episode applied just one day before UV-C stress. However, npq4 mutant plants devoid of PsbS, were not able to cross-acclimate to UV-C and memorise excess light stress, thus displayed significantly higher cell death than WT. Contrary, plants overexpressing PsbS were always acclimated to UV-C stress, regardless of prior excess light treatment or not. The quality of cell death process seems to be not affected in analysed genotypes and is always starting from chloroplast breakdown. Electrical retrograde signalling and anterograde molecular responses for induction of the cellular light memory and cell death are also specifically regulated by PsbS level and strongly correlate with transtylakoid pH-gradient changes. Obtained results suggest novel and important functions of PsbS in retrograde and antherograde regulation of cell death, cellular light memory, UV-C and excess light crosstalk.