Peach Leaf Curl Disease, caused by the fungus Taphrina deformans, is characterized by reddish hypertrophic and hyperplasic leaf areas. To comprehend the biochemical imbalances caused by the disease an integrated approach including metabolomics, lipidomics, proteomics and complementary biochemical techniques was undertaken. Symptomatic and asymptomatic areas were dissected from leaves with increasing extension of the disease. A differential metabolic behaviour was identified in symptomatic areas with respect to either asymptomatic areas or healthy leaves. Symptomatic areas showed an altered chloroplastic functioning and composition which includes decrease in the photosynthetic machinery, alteration in plastidic lipids, and decreased starch, carotenoid and chlorophyll biosynthesis. In symptomatic areas, decreases in chloroplast redox-homeostasis proteins and in triacylglycerols double bond index were observed. Proteomic data revealed an up-regulation of phenylpropanoid and mevalonate pathways and down-regulation of the plastidic methylerythritol phosphate route. Amino acid pools were affected, with up-regulation of proteins involved in asparagine synthesis. Curled areas exhibited a metabolic shift towards functioning as a sink tissue importing sugars and producing energy through fermentation and respiration and reductive power via the pentose phosphate route. As the disease progresses, reduced asymptomatic areas and healthy leaves diminishes photosynthates production thereby limiting fruit production and ultimately tree survival.

Evidence suggests that guard cells have higher rate of phosphoenolpyruvate carboxylase (PEPc)-mediated dark CO2 assimilation than mesophyll cells. However, it is unknown which metabolic pathways are activated following dark CO2 assimilation in guard cells. Furthermore, it remains unclear how the metabolic fluxes throughout the tricarboxylic acid (TCA) cycle and associated pathways are regulated in illuminated guard cells. Here we used 13C-HCO3 labelling of tobacco guard cells harvested under continuous dark or during the dark-to-light transition to elucidate principles of metabolic dynamics downstream of CO2 assimilation. Most metabolic changes were similar between dark-exposed and illuminated guard cells. However, illumination increased the 13C-enrichment in sugars and metabolites associated to the TCA cycle. Sucrose was labelled in the dark, but light exposure increased the 13C-labelling into this metabolite. Fumarate was strongly labelled under both dark and light conditions, while illumination increased the 13C-enrichment in pyruvate, succinate and glutamate. Only one 13C was incorporated into malate and citrate in either dark or light conditions. Our results collectively suggest that the PEPc-mediated CO2 assimilation provides carbons for gluconeogenesis, the TCA cycle and glutamate synthesis and that previously stored malate and citrate are used to underpin the specific metabolic requirements of illuminated guard cells.

In cellular circumstances where carbohydrates are scarce, plants can use alternative substrates for cellular energetic maintenance. In plants, the main protein reserve is present in the chloroplast, which contains most of the total leaf proteins and represents a rich source of nitrogen and amino acids. Autophagy plays a key role in chloroplast breakdown, a well-recognized symptom of both natural and stress-induced plant senescence. Remarkably, an autophagic-independent route of chloroplast degradation associated with Chloroplast Vesiculation (CV) gene was recently demonstrated. During extended darkness, CV is highly induced in the absence of autophagy, contributing to the early senescence phenotype of atg mutants. To further investigate the role of CV under dark-induced senescence conditions, mutants with low expression of CV ( amircv) and double mutants amircv1xatg5 were characterized. Following darkness treatment, no aberrant phenotypes were observed in amircv single mutants; however, amircv1xatg5 double mutants displayed early senescence and enhanced dismantling of chloroplast and membrane structures under these conditions. Metabolic characterization revealed that the functional lack of both CV and autophagy leads to higher impairment of amino acid release and differential organic acid accumulation during starvation conditions. The data obtained are discussed in the context of the role of CV and autophagy, both in terms of cellular metabolism and the regulation of chloroplast degradation.

Cells, tissues, and organs harbour complex systems to allow communication between one another. The biological rhythms can be contrasting among organs, tissues, and cells, adjusting the physiology differently along the organism‘s regions. while also synchronising flowering and metabolism. Here, we revealed that Solanum lycopersicum manifests more balanced rhythms across the whole plant than wild tomatoes. Accordingly, the leaf development program is more coordinated in this organism than in wild species, in that young S. lycopersicum leaves develop slowly in comparison to mature leaves. Young leaves from wild tomatoes display higher photosynthetic rate than mature leaves, while large metabolite accumulations occur across plant segments. Consequently, diel metabolite levels are rather similar between young and mature leaves in the wild tomato S. pennellii, whereas the expression patterns for circadian clock genes are widely contrasting between differently aged leaves. We further demonstrated that introduction of domestication alleles into the wild tomato S. pimpinellifolium appears to synchronize the development of young and mature leaves, rendering this similar to that observed for S. lycopersicum. Collectively, the strengthening of inter-organ relationships in S. lycopersicum indicates an increased synchronization of its biology, which is probably fundamental to explain its elevated yield.

Recent results suggest that metabolism-mediated stomatal closure mechanisms are important to regulate differentially the stomatal speediness between ferns and angiosperms. However, evidence directly linking mesophyll metabolism and the slower stomatal conductance (gs) in ferns is missing. Here we investigated the effect of exogenous application of abscisic acid (ABA), sucrose and mannitol on gs kinetics and carried out a metabolic fingerprinting analysis of ferns and angiosperms leaves harvested throughout a diel course. Ferns stomata did not respond to ABA in the time period analysed. No differences in the relative decrease in gs was observed between ferns and the angiosperm following provision of sucrose or mannitol. However, ferns have slower gs responses to these compounds than angiosperms. Metabolomics analysis highlights that ferns have higher accumulation of secondary rather than primary metabolites throughout the diel course, with the opposite being observed in angiosperms. Our results indicate that metabolism-mediated stomatal closure mechanism is conserved among ferns and angiosperms and that the slower stomatal closure in ferns is associated to a reduced capacity to respond to mesophyll-derived sucrose and to a higher carbon allocation toward secondary metabolism, which likely modulates both photosynthesis-stomatal movements and growth-stress tolerance trade-offs.

Nitrogen (N) is fundamental to plant growth, development, and yield. Genes underlying N utilization and assimilation are well characterized, but mechanisms underpinning plasticity of different phenotypes to varying amounts of N in the soil remain elusive. Here, using Arabidopsis thaliana accessions, we dissected the genetic architecture of plasticity in early and late rosette diameter, flowering time and yield in response to three levels of N in soil. Genome-wide association analysis identified three significant associations for phenotypic plasticity, one for early rosette diameter and two for flowering time. We confirmed that the gene At1g19880, hereafter named as PLASTICITY OF ROSETTE TO NITROGEN 1 (PROTON1), encoding for a regulator of chromatin condensation 1 (RCC1) family protein, conferred plasticity of rosette diameter in response to changes in N availability. The altered plasticities were a result of faster development under limiting N, and correlated with the plasticity in the levels of primary metabolites. By using different growth conditions for a subset of accessions, we showed that plasticities of growth and flowering-related traits in response to N availability differed between the environmental cues, indicating decoupled genetic programs regulating these traits. Our findings provide a prospective for identification of genes that stabilize performance under fluctuating environments.

The understanding of the dynamics of stomatal movements has increased substantially through genetic manipulation of plant metabolism either at the whole plant level or specifically in guard cells. However, the regulation of stomatal speediness remains not completely elucidated. Here we shown that reduced expression of guard cell sucrose synthase 2 (NtSUS2) of Nicotiana tabacum L. altered the topology and the connectivity of the guard cell metabolic network and the accumulation of metabolites positively correlated with stomatal speediness during dark-to-light transition. This leads to a slower light-induced stomatal opening, lower steady-state stomatal conductance and a strong reduction (up to 44%) in daily whole plant transpiration in the transgenics, when compared to wild type plants. Furthermore, the transgenic lines transpired more or have lower reduction in whole plant transpiration under short water deficit periods, indicating a higher effective use of water under this condition. Our results collectively suggest that the regulation of stomatal movement and speediness involve a complex modulation of the guard cell metabolic network, in which NtSUS2 has an important role. The results are discussed on the role of guard cell metabolism for the regulation of both stomatal speediness and whole plant transpiration.

Utilizing phosphate more efficiently is crucial for sustainable crop production. Highly efficient rice (Oryza sativa) cultivars have been identified and this study aims to identify metabolic markers associated with P utilization efficiency. P deficiency generally reduced leaf P concentrations and CO2 assimilation rates but efficient cultivars were reducing leaf P concentrations further than inefficient ones while maintaining similar CO2 assimilation rates. Adaptive changes in carbon metabolism were detected but equally in efficient and inefficient cultivar groups. Groups furthermore did not differ with respect to partial substitutions of phospholipids by sulfo- and galactolipids. Metabolites significantly more abundant in the efficient group, such as sinapate, benzoate and glucoronate, were related to antioxidant defense and may help alleviating oxidative stress caused by P deficiency. Sugar alcohols ribitol and threitol were another marker metabolite for higher phosphate efficiency as were several amino acids, especially threonine. Since these metabolites are not known to be associated with P deficiency, they may provide novel clues for the selection of more P efficient genotypes. In conclusion, metabolite signatures detected here were not related to phosphate metabolism but rather helped P efficient lines to keep vital processes functional under the adverse conditions of P starvation.