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.
The 18O enrichment (Δ 18O) of leaf water affects the Δ 18O of photosynthetic products such as sucrose, generating an isotopic archive of plant function and past climate. However, uncertainty remains regarding how leaf water compartmentation between photosynthetic and non-photosynthetic tissue affects the relationship between Δ 18O of bulk leaf water (Δ 18O LW) and leaf sucrose (Δ 18O Sucrose). We grew Lolium perenne (a C 3 grass) in mesocosm-scale, replicated experiments with daytime relative humidity (RH 50 or 75%) and CO 2 level (200, 400 or 800 μmol mol -1) as factors, and determined Δ 18O LW, Δ 18O Sucrose and morpho-physiological leaf parameters, including transpiration ( E leaf), stomatal conductance ( g s) and mesophyll conductance to CO 2 ( g m). The Δ 18O of photosynthetic medium water (Δ 18O SSW) was estimated from Δ 18O Sucrose and the equilibrium fractionation between water and carbonyl groups (ε bio). Δ 18O SSW was well predicted by theoretical estimates of leaf water at the evaporative site (Δ 18O e) with adjustments that correlated with gas exchange parameters ( g s or total conductance to CO 2). Isotopic mass balance and published work indicated that non-photosynthetic tissue water was a large fraction (~0.53) of bulk leaf water. Δ 18O LW was a poor proxy for Δ 18O Sucrose, mainly due to opposite Δ 18O responses of non-photosynthetic tissue water (Δ 18O non-SSW) relative to Δ 18O SSW, driven by atmospheric conditions.
Plant diseases are driven by an intricate set of defense mechanisms counterbalanced by the expression of host susceptibility factors promoted through the action of pathogen effectors. In spite of their central role in the establishment of the pathology, the primary components of plant susceptibility are still poorly understood and challenging to trace. Focusing on Fusarium head blight (FHB) in bread wheat and integrating plant transcriptomics responses from a susceptible cultivar facing Fusarium graminearum strains of different aggressiveness, we described unexpected differential expression of a conserved set of transcription factors and an original subset of master regulators were evidenced using a regulation network approach. The dual-integration with the expression data of pathogen effector genes combined with database mining, demonstrated robust connections with the plant molecular regulators and identified relevant candidate genes involved in plant immunity, mostly able to suppress plant defense mechanisms. Furthermore, taking advantage of wheat cultivars of contrasting susceptibility levels, a refined list of 142 conserved susceptibility gene candidates were proposed to be necessary host’s determinants for the establishment of a compatible interaction. In this respect, our findings provide new clues for improving FHB control in wheat and also could conceivably leverage further original researches dealing with a broader spectrum of plant pathogens.
The formation of secondary cell walls is tightly regulated spatio-temporally by various developmental and environmental signals. Successful fine-tuning of the trade-off between secondary cell wall biosynthesis and stress responses requires better understanding of how plant growth is regulated under environmental stress conditions. However, current understanding of the interplay between environmental signaling and secondary cell wall formation is limited. The lipid-derived plant hormone jasmonate (JA) and its derivatives are important signaling components involved in various physiological processes including plant growth, development, and abiotic/biotic stress response. Recent studies suggest that JA may be involved in secondary cell wall formation. We tested this hypothesis using the transcription factor MYB46, a master switch for secondary wall biosynthesis, and JA treatments. Both the transcripts and protein levels of MYB46 were significantly increased by the JA treatments, which also triggered the upregulation of MYB46 downstream genes with increased secondary wall formation. We then show that this JA-induced upregulation of MYB46 function was mediated by MYC2, a basic helix-loop-helix (bHLH) domain–containing transcription factor, which plays a pivotal role in the JA-mediated changes. We conclude that this MYC2-MYB46 module is a key component of the plant response to JA signaling.
The thylakoid membrane is in a temperature-sensitive equilibrium that shifts repeatedly during the life cycle in response to ambient temperature or solar irradiance. Plants respond to seasonal temperature by changing their thylakoid lipid composition, while a more rapid mechanism for short-term heat exposure is required. The emission of the small organic molecule isoprene has been postulated as one such possible rapid mechanism. The protective mechanism of isoprene is not known, but some plants emit isoprene during periods of high-temperature stress. In this work, we investigate the dynamics and structure for lipids within a thylakoid membrane at different temperatures and varied isoprene content using classical molecular dynamics simulations. The results are compared with experimental findings from across the literature for temperature-dependent changes in the lipid composition and shape of thylakoids. We find that the surface area, volume, and flexibility of the membrane, as well as the lipid diffusion, increase with temperature, while the membrane thickness decreases. Saturated thylakoid 34:3 glycolipids derived from eukaryotic synthesis pathways exhibit significantly different dynamics than lipids from prokaryotic synthesis paths, which could explain the upregulation of specific lipid synthesis pathways at different temperatures. Increasing isoprene concentration was not observed to have a significant thermoprotective effect on the thylakoid membranes, and that isoprene readily permeated the membrane models tested here.
Plants perceive environmental stresses as whole organisms via distant signals conveying danger messages through their vasculature. In parallel to vascular transport, airborne plant volatile compounds, including green leaf volatiles (GLVs), can bypass the lack of vascular connection. However, some small volatile compounds move through the vasculature; such vascular transport is little known about GLVs. Here we illustrate GLV alcohols as solutes move within xylem vessels in Zea mays. We describe GLV alcohols, including Z-3-hexenol and its isomer E-3-hexenol, which is not synthesized in maize, is mobilized through the transpiration stream via xylem vessels. Since transpiration is mediated by stomatal aperture, closing stomata by two independent methods diminishes the transport of GLV alcohol and its isomer. In addition, lower transport of GLV alcohols impairs their function in inducing terpenoid biosynthesis suggesting xylem transport of GLV alcohols plays a significant role in their systemic function. Our study not only shows that GLV alcohols can be transported in the xylem but points to stomatal regulation as a mechanism that climatic factors such as drought, heat, flooding, and high CO 2 levels affect systemic signaling functions of GLVs.
Brassica crops include various edible vegetable and plant oil crops, and their production is limited by low temperature beyond their tolerant capability. The key regulators of low-temperature resistance in Brassica remain largely unexplored. To identify post-transcriptional regulators of plant response to low temperature, we performed small RNA profiling, and found that 16 known miRNAs were responsive to cold treatment in Brassica rapa. The cold response of seven of those miRNAs were further confirmed by qRT-PCR and/or northern blotting analyses. In parallel, a genome-wide association study of 220 accessions of Brassica napus identified four candidate MIRNA genes, all of which were cold-responsive, at the loci associated with low temperature resistance. Specifically, these large-scale data analyses revealed a link between miR1885 and the plant response to low temperature in both B. rapa and B. napus. Using 5′ rapid amplification of cDNA ends approach, we validated that miR1885 can cleave its putative target transcripts, Bn.TIR.A09 and Bn.TNL.A03, in B. napus. Furthermore, overexpression of miR1885 in Semi-winter type B. napus decreased the mRNA abundance of Bn.TIR.A09 and Bn.TNL.A03, resulting in increased sensitivity to low temperature. Knocking down of miR1885 in Spring type B. napus led to increased mRNA abundance of its targets and improved rapeseed tolerance to low temperature. Together, our results suggested that the loci of miR1885 and its targets could be potential candidates for the molecular breeding of low temperature-tolerant Spring type Brassica crops.
Crop growth model simulates the response of photosynthetic rate to nitrogen (N) dynamic by calculating critical N concentration. However, critical N concentration cannot describe the physiological effect of N dynamic to photosynthesis. In this paper, a Two-leaf Photosynthetic Model Sensitive to Chlorophyll Content (TPMSCC) was developed and coupled with the crop growth model (WheatGrow) to improve the mechanism of N dynamics on photosynthesis. The simulating results of TPMSCC revealed the high sensitivity of LCC on photosynthesis. The relationships of LCC to the maximum photosynthetic rate (A max) and the initial light use efficiency (ɑ) simulated by TPMSCC were linear and logarithmic. In addition, canopy photosynthetic rate benefited from the increase of diffuse radiation fraction (DRF) except for the condition of dense canopy at high solar zenith angle. The optimized WheatGrow performed better than WheatGrow on describing the response of N level on biomass accumulation and distribution in different organs.
Volatile organic compounds (VOCs) may communicate stress between plants. However little appears to be documented on how such VOCs affect transpiration. Changes in transpiration in response to some VOCs was examined by measurement of flow ( Q) at high resolution into detached leaves of Vitis vinifera (cv. Shiraz) and Arabidopsis (Col 0). Sensors recorded arrival and decay of volatiles at the leaf lamina. Moderate xylem tensions were developed in V. vinifera leaves by incorporating a hydraulic resistance in the flow pathway. Simultaneous recording of leaf gas exchange (Assimilation, A, and Transpiration, E) for both V. vinifera and Arabidopsis revealed that for Arabidopsis Q was stochastically restricted by the gas exchange cuvette but not E in the short term. Depending on the applied supply pressure cavitation could be controlled in V. vinifera evident from reduced Q, and leaf wilting. Stomatal closure occurred upon cavitation after a transitory increase in E and A, and after wilting began and was reversed by re-pressurization. VOCs were emitted from leaves corresponding to changes in flow rate, and light to dark transitions but not to cavitation. Volatile methanol but not ethanol or methyl salicylate induced a localised dose-dependent reversible stomatal closure in both V. vinifera and Arabidopsis.
Plants can detect neighbouring plants through a reduction in the ratio between red and far-red light (R:FR). This provides a signal of plant-plant competition and induces rapid plant growth while inhibiting defence against biotic stress, two interlinked responses designated as the shade avoidance syndrome (SAS). Consequently, the SAS can influence plant-herbivore interactions that could cascade to higher trophic levels. However, little is known on how the expression of the SAS can influence tritrophic interactions. We investigated whether changes in R:FR affect the emission of herbivore-induced plant volatiles (HIPVs), and whether these changes influence the attraction of the zoophytophagous predator Macrolophus pygmaeus. We also studied how the expression of the SAS and subsequent inhibition of plant defences affects the reproduction of M. pygmaeus in both the presence and absence of the greenhouse whitefly ( Trialeurodes vaporariorum) as arthropod prey. The results show that changes in R:FR have little effect on HIPV emissions and predator attraction. However, a reduction in R:FR leads to increased reproduction of both the predator and the whiteflies. We conclude that shade avoidance responses can increase the population development of M. pygmaeus directly by reducing plant defences, and indirectly by supporting higher herbivore densities.
CO 2-induced chloroplast movement was reported in the monograph by Gustav Senn in 1908: unilateral CO 2 supply to the one cell-layered moss leaves induced the positively CO 2-tactic periclinal arrangement of chloroplasts. However, from the modern criteria, several experimental settings are unacceptable. Here, using a model moss plant Physcomitrium patens, we examined basic features of chloroplast CO 2-tactic relocation with a modernized experimental system. The CO 2 relocation was light-dependent and especially the CO 2 relocation in red light was substantially dependent on photosynthetic activity. Between the cytoskeletons responsible for chloroplast movement of P. patens, the microfilament mainly worked for CO 2 relocation, but the microtubule-based movement was insensitive to CO 2. The CO 2 relocation was induced not only by air with and without CO 2 but also by the more realistic difference in CO 2 concentration between the two sides. In the leaves placed on the surface of a gel sheet, chloroplasts avoided the gel side and positioned in the air facing surface. This was also shown to be photosynthesis dependent. Based on these observations, we propose a working hypothesis that the threshold light intensity between the light-accumulation and -avoidance responses of the photorelocation would be increased by CO 2, resulting in the CO 2-tactic relocation of chloroplast.
Eight species in the Namib Desert, South Africa were assessed for their leaf area ( A), thickness ( z), saturated ( Q) and dry mass, relative volume of air ( F a), water and dry mass, intrinsic water-use efficiency (based on δ 13C), and N, P and cation (Na+K) contents. As water-storage capacity is a function of Q v and z, this means Q/ A (= Q v • z) is an ideal index of succulence compared with specific-leaf-area and other indices that highlight mass rather than volume. Specific gravity ( ρ l) has a different relationship with the F a of sclero-mesophylls: rising ρ l infers decreasing air content is replaced by water rather than dry matter. The trend among succulent species, including Argentinian/Spanish added to our study, was Q/ A exceeding 1 mg water/mm 2 whose overall slope was ten times that for co-occurring sclerophyll-mesophyll species, and shows the futility of seeking a universal relationship among plants regarding their water-storing properties. (Na+K), N and P concentrations varied on a dry-matter, but not water-volume, basis. W i relationships were essentially functions of variations in z and increased metabolic efficiency. We conclude that z and Q v are keys to the special physiological properties of succulent leaves. Adding succulents would force many current monotonic relationships to dichotomize.
The combined study of C and O isotopes in plant organic matter has emerged as a powerful tool for understanding plant functional responses to environmental change. The approach relies on established relationships between leaf gas exchange and isotopic fractionation to derive a series of model scenarios that can be used to infer changes in photosynthetic assimilation and stomatal conductance driven by changes in environmental parameters (CO2, water availability, air humid-ity, temperature, nutrients). We review the mechanistic basis for a conceptual model, in light of recently published research, and discuss where isotopic observations don’t match our current understanding of plant physiological response to environment. We demonstrate that 1) the mod-el was applied successfully in many, but not all studies, 2), while originally conceived for leaf isotopes, the model has been applied extensively to tree ring isotopes in the context of tree physiology and dendrochronology. Where isotopic observations deviate from physiologically plau-sible conclusions, this mismatch between gas-exchange and isotope response provides valuable insights on underlying physiological processes. Overall, we found that isotope responses can be grouped into situations of increasing resource limitation versus higher resource availability. The dual isotope model helps to interpret plant responses to a multitude of environmental factors.
Stomata are the key nodes linking photosynthesis and transpiration. By regulating the opening degree of stomata, plants successively achieve the balance between water loss and carbon dioxide acquisition. The dynamic behavior of stomata is an important cornerstone of plant adaptability. Though there have been miscellaneous experimental results on stomata and their constituent cells, the guard cells and the subsidiary cells, current theory of stomata regulation is far from clear and unified. In this work, we develop an integrated model to describe the stomatal dynamics of seed plants based on existing experimental results. The model includes three parts: 1) a passive mechanical model of the stomatal aperture as a bivariate function of the guard-cell and the subsidiary-cell turgor pressures; 2) an active regulation model with a targeted ion-content in guard cells as a function of their water potential; and 3) a dynamical model for the movement of potassium ions and water content. Our model has been used to reproduce different experimental phenomena semi and stomatal responses to environment conditions.
Conservative flowering behaviors, such as flowering during long days in summer or late flowering at a high leaf number, are often proposed to protect against variable winter and spring temperatures which lead to frost damage if premature flowering occurs. Yet, due the many factors in natural environments relative to the number of individuals compared, assessing which climate characteristics drive these flowering traits has been difficult. We applied a multidisciplinary approach to ten winter-annual Arabidopsis thaliana populations originating along a wide climactic gradient in Norway. We used a variable reduction strategy to assess which of 100 climate descriptors from their home sites correlated most to their behaviors when grown in common garden and assessed sequence variation of 19 known environmental-response flowering genes. Photoperiod sensitivity inversely correlated with interannual variation in timing of growing season onset (start of favorable spring temperatures). Time to flowering appeared driven by growing season length, curtailed by cold fall temperatures. The distribution of FLM, TFL2, and HOS1 haplotypes, genes involved in ambient temperature response, correlated with growing-season climate. We show that long-day sensitivity and late flowering may be driven not by risk of spring frosts, but by growing season temperature and length perhaps to opportunistically maximize growth.
Drought and high salinity are major environmental factors that reduce plant growth and development, leading to loss of plant productivity in agriculture. Under these stress conditions, photosynthesis is greatly suppressed despite the high cellular energy cost of stress response processes. Currently, the process that allows plants to secure the energy required for osmotic stress responses remains elusive. Here, we provide evidence that CBR1, a cytochrome b5 reductase, plays an important role in ATP production in response to NaCl and dehydration stresses. Overexpression and loss of function of CBR1 led to enhanced resistance and sensitivity, respectively, to osmotic stress. Upon exposure to osmotic stress, CBR1 was localized to the endoplasmic reticulum (ER) instead of to mitochondria, where it was localized under normal conditions. Transgenic plants overexpressing ER-targeted CBR1, but not mitochondria-targeted CBR1, showed enhanced resistance to osmotic stress and higher expression of SOS1/2/3 and RD29A/B under osmotic stress. CBR1-ER and CBR1-OX plants, but not CBR1-MT plants, had higher levels of ATP and unsaturated fatty acids under osmotic stress. Moreover, these effects were abrogated by thioridazine and 2-deoxy glucose, inhibitors of β-oxidation and glycolysis, respectively, but not by thiazolidinedione, an inhibitor of the mitochondrial pyruvate transporter. Based on these results, we propose that ER-localized CBR1 triggers ATP production via the production and β-oxidation of polyunsaturated fatty acids under osmotic stress.
Increasing atmospheric CO 2 and drought are major symptoms of anthropogenic climate change with profound effects on plant growth. Transgenerational memory (i.e. influence of the parental environment on offspring phenotype and performance) has been suggested as a relevant mechanism for plants to build-up adaptative capacity for rapid environmental changes. However, this mechanism of pre-adaptation remains poorly investigated so far. We investigated intra- and transgenerational effects of elevated CO 2 on drought response of wheat. We used seeds from a FACE (Free Air Carbon Dioxide Enrichment) experiment with ambient and elevated CO 2 to grow plants in climate chambers in which we varied CO 2, atmospheric water demand and soil moisture. We quantified photosynthetic efficiency, stomatal sensitivity and biomass production. We observed intragenerational upregulation of photosynthetic efficiency but transgenerational downregulation of photosynthetic efficiency, stomatal sensitivity and water use efficiency as response to maternally elevated CO 2. Plant biomass was affected by drought and experimental CO 2 but not by maternal CO 2. Our study showcases the importance of transgenerational memory effects when studying climate change response of plants and could have major implications for our understanding of global dynamics of carbon sequestration. It highlights the pressing need for multi-generational experiments accounting for transgenerational memory effects of elevated CO 2.
Upland rice (Oryza sativa) is adapted to strongly phosphorus (P) sorbing soils. The mechanisms underlying P acquisition, however, are not well understood, and models typically underestimate uptake. This complicates root ideotype development and trait-based selection for further improvement. We present a novel model, which correctly simulates the P uptake by a P-efficient rice genotype measured over 48 days of growth. The model represents root morphology at the local rhizosphere scale, including root hairs and fine S-type laterals. It simulates fast-and slowly reacting soil P and the P-solubilizing effect of root-induced pH changes in the soil. Simulations predict that the zone of pH changes and P solubilization around a root spreads further into the soil than the zone of P depletion. A root needs to place laterals outside its depletion-but inside its solubilization zone to maximize P uptake. S-type laterals, which are short but hairy, appear to be the key root structures to achieve that. Thus, thicker roots facilitate the P uptake by fine lateral roots. Uptake can be enhanced through longer root hairs and greater root length density but was less sensitive to total root length and root class proportions.