MYB12 promotes flavonol biosynthesis in plants by targeting several early biosynthesis genes (EBGs) of this pathway. The transcriptions of these EBGs are also induced by sucrose signal. However, whether MYB12 is activated by sucrose signal and the other roles of MYB12 in regulating plant metabolism are poorly understood. In this study, two NtMYB12 genes were cloned from Nicotiana tabacum. Both NtMYB12a and NtMYB12b are involved in regulating flavonoids biosynthesis in tobacco. NtMYB12a is further shown to inhibit the accumulation of fatty acid (FA) in tobacco leaves and seeds. Posttranslational activation and chromatin immunoprecipitation assays demonstrate that NtMYB12a directly promotes the transcriptions of NtLOX6, NtLOX5, NtSFAR4, and NtGDSL2, which encode lipoxygenase (LOX) or lipase enzymes catalyzing the degradation of FA. NtLOX6 and NtLOX5 are shown to prevent the accumulation of FA in the mature seeds, and significantly reduced the percentage of polyunsaturated fatty acids (PUFAs) in tobacco. Sucrose stimulates the transcription of NtMYB12a, and loss function of NtMYB12a partially suppresses the decrease of FA content in tobacco seedlings caused by sucrose treatment. The regulation of sucrose on the expression of NtLOX6 and NtGDSL2 genes is mediated by NtMYB12a, but those of NtLOX5 and NtSFAR4 genes are independent of sucrose.
We explored the effects, on photosynthesis in cowpea (Vigna unguiculata), of high temperature and light — environmental stresses that often co-occur under field conditions. We observed contrasting responses in the light and carbon assimilatory reactions, whereby in high temperature, the light reactions were stimulated while CO2 assimilation was substantially reduced. There were two striking observations. First, the primary quinone acceptor (QA), a measure of the regulatory balance of the light reactions, became more oxidized with increasing temperature, suggesting increased electron sink capacity, despite the reduced CO2 fixation. Second, a strong, O2-dependent inactivation of assimilation capacity, consistent with down-regulation of rubisco under these conditions, a phenomenon that has not been previously reported. The dependence of these effects on CO2, O2 and light led us to conclude that both photorespiration and an alternative electron acceptor, supported increased electron flow, and thus provided photoprotection, under these conditions. Further experiments showed that the increased electron flow was maintained by rapid rates of PSII repair, particularly at combined high light and temperature. Overall, the results suggest that photodamage to the light reactions can be avoided under high light and temperatures by increasing electron sink strength, even when assimilation is strongly suppressed.
Photosynthesis is especially sensitive to environmental conditions and the composition of the photosynthetic apparatus can be modulated in response to environmental change, a process termed photosynthetic acclimation. Previously, we identified a role for a cytosolic fumarase, FUM2 in acclimation to low temperature in Arabidopsis thaliana. Mutant lines lacking FUM2 were unable to acclimate their photosynthetic apparatus to cold. Here, using gas exchange measurements and metabolite assays of acclimating and non-acclimating plants, we show that acclimation to low temperature results in a change in the distribution of photosynthetically fixed carbon to different storage pools during the day. Proteomic analysis of wild-type Col-0 Arabidopsis and of a fum2 mutant which was unable to acclimate to cold indicates that extensive changes occurring in response to cold are affected in the mutant. Metabolic and proteomic data were used to parameterise metabolic models. Using an approach called flux sampling, we show how the relative export of triose phosphate and 3-phsphoglycerate provides a signal of the chloroplast redox state that could underly photosynthetic acclimation to cold.
The phenomenon that organisms can distinguish genetically related individuals from strangers (i.e. kin recognition) and exhibit more cooperative behaviors towards their relatives has been documented in a wide variety of organisms. But its occurrence in plants has only been recently considered. What emerges is that, while concerns remain about some methodologies used to document kin recognition, there is sufficient evidence to state that it exists in plants. Effects of kin recognition go well beyond reducing resource competition between related plants, and involve interactions with pollinators, pests and diseases as well as symbionts (mycorrhizal networks). It thus likely has important implications for diversity of plant populations, ecological networks and community structure. Such effects need to be further explored. Moreover, as kin selection may result in less competitive traits and thus greater population performance, it also holds promise for crop breeding. However, one would need to consider that (i) growing crops of strongly related plants will evidently forego advantages of crop diversification and (ii) outcomes of kin recognition tend to depend on environmental conditions. Therefore, the primary questions that need to be answered are: when, where and by how much kin recognition improves population performance.
Plant roots interact with rhizosphere microbes to accelerate soil organic matter (SOM) mineralization and promote nutrient acquisition. Root-mediated changes in SOM turnover largely depend on root-C input and soil nutrient availability. Hence, interspecific competition and nutrient uptake dynamics over plant development stages as well as spatiotemporal variability in C input may modify SOM turnover. To investigate the effect of intraspecific competition on SOM mineralization at three growth stages (heading, flowering and ripening), we grew maize (C4 plant) under three planting densities on a C3 soil. 13C-natural abundance and 15N-pool dilution were applied in situ to determine C- and N-mineralization rates. Soil C- and N-mineralization rates were tightly coupled and peaked at maize flowering. However, the C-to-N-mineralization ratio increased with N, indicating that microbes mineralize N-rich components to mine SOM for N. Furthermore, intraspecific competition did not affect root biomass; instead, plants shaped root morphology towards higher specific root length as an efficient strategy competing for nutrient. Hence, root morphologic traits rather than root biomass per se were positively related to C- and N-mineralization. Overall, plant competition for nutrients controlled the intensity and mechanisms of soil C- and N-turnover by the adaptation of root traits and nutrient depletion.
Light is important for plant life as a source of energy to drive photosynthesis but also as an environmental signal regulating development or cellular events such as resetting of the circadian clock. Light itself can cause stress such as excess light, fluctuating light, photoperiod and ultraviolet light stress. Light quality, quantity and light duration are important sources of information to prepare plants for future light stress events. Recurring light stress results in acclimation processes to the changing light environment. Furthermore, light regulates the responses of plants to diverse biotic and abiotic stresses. For example, short day conditions or shady environments prime thermotolerance and increase cold acclimation. Similarly, during drought stress, light signaling is important for the plant´s stress response. Additionally, the light environment affects the plant´s responses to biotic intruders such as pathogens or insect herbivores. Light influence many stress responses resulting in positive growth-defense trade-offs. Under shade, however, plants prioritize growth over defense and stress responses. In this review, we summarize the impact of light as a stressor and its influences on abiotic and biotic stress responses with special focus on the role of the different light receptors and the crosstalk between light signaling components and stress response pathways.
Intracellular levels of Mg2+ are tightly regulated, as Mg2+ deficiency or excess affects normal plant growth and development. In Arabidopsis, we determined that phospholipase Dα1 (PLDα1) is involved in the stress response to high-magnesium conditions. The T-DNA insertion mutant pldα1 is hypersensitive to increased concentrations of magnesium, exhibiting reduced primary root length and fresh weight. PLDα1 activity increases rapidly after high-Mg2+ treatment, and this increase was found to be dose-dependent. Two lines harboring mutations in the HKD motif, which is essential for PLDα1 activity, displayed the same high-Mg2+ hypersensitivity of pldα1 plants. Moreover, we show that high concentrations of Mg2+ disrupt K+ homeostasis, and that transcription of K+ homeostasis-related genes CIPK9 and HAK5 is impaired in pldα1. Additionally, we found that the akt1, hak5 double mutant is hypersensitive to high-Mg2+. We conclude that in Arabidopsis, the enzyme activity of PLDα1 is vital in the response to high-Mg2+ conditions, and that PLDα1 mediates this response partially through regulation of K+ homeostasis.
Gross primary production (GPP) is a key component of the forest carbon cycle. However, our knowledge of GPP at the stand scale remains uncertain because estimates derived from eddy covariance (EC) rely on semi-empirical modeling and the assumptions of the EC technique are sometimes not fully met. We propose using the sap flux/isotope method as an alternative way to estimate canopy GPP, termed GPPiso/SF, at the stand scale and at daily resolution. It is based on canopy conductance inferred from sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPPiso/SF estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPPiso/SF to the GPP derived from PRELES, a model parameterised with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilised and a reference plot. The resulting annual and daily GPPiso/SF estimates agreed well with PRELES, in the fertilised plot and the reference plot. We discuss the GPPiso/SF method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met.
The phosphorylation states of two serine residues within the C-terminal domain of AtPIP2;1 (S280, S283) regulate its trafficking to the plasma membrane in response to salt and osmotic stress. Here we investigated whether the phosphorylation states of S280 and S283 also influence AtPIP2;1 facilitated water and cation transport. A series of single and double S280 and S283 phospho-mimic and -deficient AtPIP2;1 mutants were tested in heterologous systems. In Xenopus laevis oocytes, phospho-mimic mutants AtPIP2;1 S280D, S283D and S280D/S283D, had significantly greater ion conductance for Na+ and K+, whereas the S280A single and S280A/S283A double mutants, had greater water permeability. A phospho-mimic-dependent inverse relationship between AtPIP2;1 water and ion transport with a 10-fold change in both was observed. These results revealed that phosphorylation of S280 and S283 influences the preferential facilitation between ion and water permeability by AtPIP2;1. The results also hint at other sites playing a role that are yet to be elucidated. Expression of the phospho-mimic AtPIP2;1 mutants in Saccharomyces cerevisiae, confirmed that phosphorylation influences plasma membrane localisation, and revealed higher Na+ accumulation for S280A and S283D. Collectively, the results show that phosphorylation in the C-terminal domain of AtPIP2;1 influences its subcellular localisation and cation transport capacity.
Leaf stomatal density is known to covary with leaf vein density. However, the functional underpinning of this relation, and how it scales to whole-plant water transport anatomy, is still unresolved. We hypothesized that the balance of water exchange between the vapour phase (in stomata) and liquid phase (in vessels) depends on the consistent scaling between the summed stomatal areas and xylem cross-sectional areas, both at the whole-plant and single-leaf level. This predicted size-covariation should be driven by the covariation of numbers of stomata and terminal vessels. We examined the relationships of stomatal traits and xylem anatomical traits from the entire plant to individual leaves across seedlings of 53 European woody angiosperm species. There was strong and convergent scaling between total stomatal area and stem xylem area per plant and between leaf total stomatal area and midvein xylem area per leaf across all the species, irrespective of variation in leaf habit, growth-form or relative growth rate (RGR). Moreover, strong scaling was found between stomatal number and terminal vessel number while not in their respective average areas. Our findings have broad implications for integrating xylem architecture and stomatal distribution, and deepen our understanding of the design rules of plants’ water transport network.
During the later stages of seed maturation, two key adaptive traits are acquired that contribute to seed lifespan and dispersal, longevity and dormancy. The seed-specific heat shock transcription factor A9 is an important hub gene in the transcriptional network of late seed maturation. Here we demonstrate that HSFA9 plays a role in thermotolerance rather than in ex situ seed conservation. Storage of hsfa9 seeds of Medicago truncatula and Arabidopsis had comparable lifespan at moderate storage relative humidity (RH), whereas at high RH, hsfa9 seeds lost their viability much faster than wild type seeds. Furthermore, we show that in M. truncatula, Mthsfa9 seeds acquired more dormancy during late maturation than wild type. Transient expression of MtHSFA9 in hairy roots and transcriptome analysis of Mthsfa9 Tnt1 insertion mutants identified a deregulation of genes involved in ABA biosynthesis, catabolism and signalling. Consistent with these results, Mthsfa9 seeds exhibited increased ABA levels and higher sensitivity to ABA. These data suggest that in legumes, HSFA9 acts as a negative regulator of the depth of seed dormancy during seed development via the modulation of hormonal balance.
Abstract: At the genus and species level, variation in root anatomy and architecture may interact to affect strategies of drought avoidance. To investigate this idea, root anatomy and architecture of the drought-sensitive common bean (Phaseolus vulgaris) and drought-adapted tepary bean (Phaseolus acutifolius) were analyzed in relation to water use under terminal drought. Intraspecific variation for metaxylem anatomy and axial conductance was found in the roots of both species. Genotypes with high-conductance root metaxylem phenotypes acquired and transpired more water per unit leaf area, shoot mass, and root mass than genotypes with low-conductance metaxylem phenotypes. Interspecific variation in root architecture and root depth was observed where P. acutifolius has a deeper distribution of root length than P. vulgaris. In the deeper-rooted P. acutifolius, genotypes with high root conductance were better able to exploit deep soil water than genotypes with low root axial conductance. Contrastingly, in the shallower-rooted P. vulgaris, genotypes with low root axial conductance had improved water status through conservation of soil moisture for sustained water capture later in the season. These results indicate that metaxylem morphology interacts with root system depth to determine a strategy of drought avoidance and illustrate synergism among architectural and anatomical phenotypes for root function.
In habitats with low water availability, a fundamental challenge for plants will be to maximize photosynthetic C-gain whilst minimizing transpirational water-loss. This tradeoff between C-gain and water-loss can in part be achieved through the coordination of leaf-level photosynthetic and hydraulic traits. To test the relationship of photosynthetic C-gain and transpirational water-loss we grew under common growth conditions 18 C4 grasses adapted to habitats with different mean annual precipitation (MAP) and measured leaf-level structural and anatomical traits associated with mesophyll conductance (gm) and leaf hydraulic conductance (Kleaf). The C4 grasses adapted to lower MAP showed greater mesophyll surface area exposed to intercellular air spaces (Smes) and adaxial stomatal density (SDada) which supported greater gm. These grasses also showed greater leaf thickness and vein-to-epidermis distance which may lead to lower Kleaf. Collectively, these leaf traits associated with gm and Kleaf scaled positively with photosynthetic rates (Anet) and leaf-level water-use efficiency (WUE) with low MAP adapted grasses exhibiting greater Anet and WUE. In summary, we identify a suite of leaf-level traits that appear important for adaptation of C4 grasses to habitats with low MAP and may be useful to identify C4 species showing greater Anet and WUE in drier conditions.
Aphids often carry facultative symbionts to achieve diverse advantages. Serratia symbiotica, one of facultative endosymbionts, increases aphid tolerance to heat. However, whether it benefits aphid colonization on host plants is yet to be determined. In the current study, we found that Acyrthosiphon pisum harboring S. symbiotica had longer feeding duration on Medicago truncatula than Serratia-free aphids. Contrastingly, Serratia-free aphids triggered higher accumulation of ROS, jasmonic acid and salicylic acid responsive genes and cytosolic Ca2+ elevations than Serratia-infected aphids. Transcriptomic analysis of salivary glands indicated that a histidine-rich Ca2+-binding protein-like gene (ApHRC) was expressed more highly in the salivary gland of Serratia-infected aphids than that of Serratia-free aphids. Once ApHRC was silenced, Serratia-infected aphids also displayed shorter phloem-feeding duration and caused Ca2+ elevation and ROS accumulation in plants. Our results suggest that ApHRC, a potential effector up-regulated by S. symbiotica in the salivary glands, evaded plant defense response by suppressing Ca2+ elevation and ROS accumulation, allowing colonization of aphids. This study has provided a revolutionary insight into how facultative symbionts facilitate aphid colonization and adaption to host plants.
Gastrodia elata, a fully mycoheterotrophic orchid without photosynthetic ability, only grows symbiotically with the fungus Armillaria. The mechanism of carbon distribution in this mycoheterotrophy is unknown. We detected high sucrose concentrations in all stages of Gastrodia tubers, suggesting sucrose may be the major sugar transported between fungus and orchid. Thick symplasm-isolated wall interfaces in colonized and adjacent large cells implied involvement of sucrose importers. Two sucrose transporter (SUT)-like genes, GeSUT4 and GeSUT3, were identified that are highly expressed in young Armillaria-colonized tubers. Yeast complementation and radio tracer experiments confirmed that GeSUT4 functioned as a high-affinity sucrose-specific proton-dependent importer. Plasma-membrane/tonoplast localization of GeSUT4-GFP fusions, and high RNA expression of GeSUT4 in symbiotic and large cells indicated that GeSUT4 likely functions in active sucrose transport for intercellular allocation and intracellular homeostasis. Transgenic Arabidopsis overexpressing GeSUT4 had larger leaves but sensitive to excess sucrose and roots were colonized with fewer mutualistic Bacillus, supporting the role of GeSUT4 in regulating sugar allocation. This is not only the first documented carbon import system in a mycoheterotrophic interaction, but also highlights the evolutionary importance of sucrose transporters for regulation of carbon flow in all types of plant-microbe interactions.
The polysaccharidic mucilage is a widespread plant trait with diverse features, often present around plant structures in contact with the environment, providing numerous functions including protection and adhesion. In myxodiasporous species, a mucilage is released upon the imbibition of the seed (myxospermy) or the fruit (myxocarpy), and therefore can play roles in the early seedling stages. It is unclear whether myxodiaspory has one or multiple evolutionary origins and why it disappeared in several species. Here, we summarize the recent advances on (i) the mucilage and mucilage secretory cell diversity, (ii) the evolution of the molecular actors involved in myxospermy underlying the observed inter- and intra-species natural diversity and (iii) the recently identified ecological functions. At the intra-species level, a high polymorphism was detected for a few genes in relation to the observed morphological diversity. Well characterized transcriptions factors interact in master regulatory complexes to balance carbon partitioning in Arabidopsis thaliana seeds. These transcription factors were sequentially recruited during seed plant evolution to control diverse traits including myxospermy, and their functions in seeds seem to be conserved across Rosids. Historically, the ecological functions of seed mucilage were mostly related to germination and seed dissemination but recently some exosystemic functions were uncovered such as soil micro-organism control and plant establishment support.
Knowing how switchgrass (Panicum virgatum L.) responds and adapts to phosphorus (P)-limitation will aid efforts to optimize P-efficiency in this species for sustainable biomass production. This integrative study investigated the impacts of mild, moderate, and severe P-stress on genome transcription and whole-plant metabolism, physiology and development in an unprecedented way for this species. P-limitation reduced overall plant growth, increased root/shoot ratio, increased root branching at moderate P-stress, and decreased root diameter with increased density and length of root hairs at severe P-stress. RNA-seq analysis revealed thousands of genes that were differentially expressed under moderate and severe P-stress in roots and/or shoots compared to P-replete plants, with many stress-induced genes involved in transcriptional and other forms of regulation, primary and secondary metabolism, transport, and other processes involved in P-acquisition and homeostasis. Amongst the latter were multiple miRNA399 genes and putative targets of these. Metabolite profiling showed that levels of most sugars and sugar alcohols decreased with increasing P stress, while organic and amino acids increased under mild and moderate P-stress in shoots and roots, although this trend reversed under severe P-stress, especially in shoots.