Comparative proteomics analyses of intraspecific differences in the response of Stipa purpurea to drought

Dryness weakens the positive effects of plant and fungal β diversities on above- and belowground biomass

Plant and microbial diversity are key to determine ecosystem functioning. Despite the well-known role of local-scale α diversity in affecting vegetation biomass, the effects of community heterogeneity (β diversity) of plants and soil microbes on above- and belowground biomass (AGB and BGB) across contrasting environments still remain unclear. Here, we conducted a dryness-gradient transect survey over 3000 km across grasslands on the Tibetan Plateau. We found that plant β diversity was more dominant than α diversity in maintaining higher levels of AGB, while soil fungal β diversity was the key driver in enhancing BGB. However, these positive effects of plant and microbial β diversity on AGB and BGB were strongly weakened by increasing climatic dryness, mainly because higher soil available phosphorus caused by increasing dryness reduced both plant and soil fungal β diversities. Overall, these new findings highlight the critical role of above- and belowground β diversity in sustaining grassland biomass, raising our awareness to the ecological risks of large-scale biotic homogenization under future climate change.

Functional Characterization of the Stipa purpurea P5CS Gene under Drought Stress Conditions

Free proline has multiple functions in plant cells, such as regulating osmotic potential and protecting both proteins and cell membranes. The expression of Δ1-Pyrroline-5-carboxylate synthase (P5CS), a key enzyme in the proline biosynthetic pathway, increases under drought, salt and cold stress conditions, causing plant cells to accumulate large amounts of proline. In this study, we cloned and identified the P5CS gene from Stipa purpurea, which has a full-length of 2196 bp and encodes 731 amino acids. A subcellular localization analysis indicated that SpP5CS localized to the cytoplasm. The ectopic overexpression of SpP5CS in Arabidopsis thaliana resulted in higher proline contents, longer roots, higher survival rates and less membrane damage under drought stress conditions compared with wild-type controls. SpP5CS-overexpressing A. thaliana was more resistant to drought stress than the wild type, whereas the deletion mutant sp5cs was less resistant to drought stress. Thus, SpP5CS may be a potential candidate target gene for increasing plant resistance to drought stress.

Differences in leaf physiological and morphological traits between Camellia japonica and Camellia reticulata

Plants of the genus Camellia are widely cultivated throughout the world as ornamentals because of their bright and large flowers. The widely cultivated varieties are mainly derived from the mutant lines and hybrid progenies of Camellia japonica Linn. and Camellia reticulata Lindl. While their geographical distributions and environmental adaptabilities are significantly different, no systematic comparison has been conducted between these two species. To investigate differences in how these plants have adapted to their environments, we measured photosynthesis and 20 leaf functional traits of C. japonica and C. reticulata grown under the same conditions. Compared with C. japonica, C. reticulata showed higher values for light saturation point, light-saturated photosynthetic rate, leaf dry mass per unit area and stomatal area, but lower values for apparent quantum efficiency, leaf size, stomatal density and leaf nitrogen content per unit mass. Stomatal area was positively correlated with light-saturated photosynthetic rate and light saturation point, but negatively correlated with stomatal density. The differences between C. reticulata and C. japonica were mainly reflected in their adaptations to light intensity and leaf morphological traits. C. reticulata is better adapted to high light intensity than C. japonica. This difference is related to the two species' differing life forms. Thus, leaf morphological traits have played an important role in the light adaptation of C. reticulata and C. japonica, and might be first noticed and selected during the breeding process. These findings will contribute to the cultivation of camellia plants.

Physiological and comparative proteomic analysis provides new insights into the effects of shade stress in maize (Zea mays L.)

BACKGROUND

Shade stress, a universal abiotic stress, suppresses plant growth and production seriously. However, little is known regarding the protein regulatory networks under shade stress. To better characterize the proteomic changes of maize leaves under shade stress, 60% shade (S) and supplementary lighting (L) on cloudy daylight from tasseling stage to physiological maturity stage were designed, the ambient sunlight treatment was used as control (CK). Isobaric tag for relative and absolute quantification (iTRAQ) technology was used to determine the proteome profiles in leaves.

RESULTS

Shading significantly decreased the SPAD value, net photosynthetic rate, and grain yield. During two experimental years, grain yields of S were reduced by 48 and 47%, and L increased by 6 and 11%, compared to CK. In total, 3958 proteins were identified by iTRAQ, and 2745 proteins were quantified including 349 proteins showed at least 1.2-fold changes in expression levels between treatments and CK. The differentially expressed proteins were classified into photosynthesis, stress defense, energy production, signal transduction, and protein and amino acid metabolism using the Web Gene Ontology Annotation Plot online tool. In addition, these proteins showed significant enrichment of the chloroplasts (58%) and cytosol (21%) for subcellular localization.

CONCLUSIONS

60% shade induced the expression of proteins involved in photosynthetic electron transport chain (especially light-harvesting complex) and stress/defense/detoxification. However, the proteins related to calvin cycle, starch and sucrose metabolisms, glycolysis, TCA cycle, and ribosome and protein synthesis were dramatically depressed. Together, our results might help to provide a valuable resource for protein function analysis and also clarify the proteomic and physiological mechanism of maize underlying shade stress.

Predicting Leaf Trait Variability as a Functional Descriptor of the Effect of Climate Change in Three Perennial Grasses

Aims of the study: The most important trends of the current climate variability is the scarcity of rains that affects arid ecosystems. The aim of this study was to explore the variability of leaf functional traits by which grassland species survive and resist drought and to investigate the potential link between resource use efficiency and water scarcity resistance strategies of species. Methods: Three grasses (Cenchrus ciliaris (C4), Stipa parviflora and Stipa lagascae (C3)) were established in a randomized block consisting of eleven replications. The seedlings were kept under increasing levels of water stress. In addition to their functional leaf traits, the rate of water loss and dimensional shrinkage were also measured. Key Results: Thicker and denser leaves, with higher dry matter contents, low specific leaf area and great capacity of water retention are considered among the grasses’ strategies of dehydration avoidance. Significant differences between the means of the functional traits were obtained. Furthermore, strong correlations among leaf traits were also detected (Spearman’s r exceeding 0.8). Conclusions: The results provide evidence that the studied grasses respond differently to drought by exhibiting a range of interspecific functional strategies that may ameliorate the resilience of grassland species communities under extreme drought events.

Methodology of Drought Stress Research: Experimental Setup and Physiological Characterization

Drought is one of the major stress factors affecting the growth and development of plants. In this context, drought-related losses of crop plant productivity impede sustainable agriculture all over the world. In general, plants respond to water deficits by multiple physiological and metabolic adaptations at the molecular, cellular, and organism levels. To understand the underlying mechanisms of drought tolerance, adequate stress models and arrays of reliable stress markers are required. Therefore, in this review we comprehensively address currently available models of drought stress, based on culturing plants in soil, hydroponically, or in agar culture, and critically discuss advantages and limitations of each design. We also address the methodology of drought stress characterization and discuss it in the context of real experimental approaches. Further, we highlight the trends of methodological developments in drought stress research, i.e., complementing conventional tests with quantification of phytohormones and reactive oxygen species (ROS), measuring antioxidant enzyme activities, and comprehensively profiling transcriptome, proteome, and metabolome.

Drought weakens the positive effects of defoliation on native rhizomatous grasses but enhances the drought-tolerance traits of native caespitose grasses

The objective of this study was to evaluate the drought tolerance, compensatory growth, and different plant traits between two native perennial caespitose grasses and two native rhizomatous grasses in response to drought and defoliation. A randomized complete block design at the Swift Current Research and Development Centre (SCRDC) of Agriculture and Agri-Food Canada (AAFC) examined the effects of water stress and clipping on the plant biomass, plant morphological traits, and relative leaf chlorophyll content (SPAD value) of four native grasses (caespitose grass: Hesperostipa comata and H. curtiseta; rhizomatous grass: Pascopyrum smithii and Elymus lanceolatus). Drought drastically decreased the shoot and root biomass, plant height, number of tillers and leaf growth of P. smithii and E. lanceolatus, as well as the rhizome biomass and R/S ratio of P. smithii. Defoliation had a positive effect on the shoot biomass of P. smithii and E. lanceolatus under well water treatments (100% and 85% of field capacity). However, the compensatory growth of P. smithii and E. lanceolatus significantly declined with increased water stress. In addition, there are no significant changes in plant biomass, plant height, number of tillers and leaves, and SPAD value of H. comata and H. curtiseta under relative dry condition (70% of field capacity). Consequently, these results demonstrated that the rhizomatous grasses possessed a stronger compensation in response to defoliation under wet conditions, but the positive effects of defoliation can be weakened by drought. The caespitose grasses (Hesperostipa species) exhibited a greater drought tolerance than rhizomatous grasses due to the relatively stable plant traits in response to water stress.

Molecular cloning of a plasma membrane aquaporin in Stipa purpurea, and exploration of its role in drought stress tolerance

Stipa purpurea is widely distributed on the Tibetan Plateau, and has high drought resistance. Plasma membrane intrinsic proteins are a type of aquaporin. They regulate the movement of water and are associated with plant protective reactions to biotic and abiotic stresses. We characterized a plasma membrane intrinsic protein from S. purpurea (SpPIP1) and elucidated its role in molecular aspects of the plant's response to drought stress. The full-length open reading frame of SpPIP1 was 870 bp and encoded 289 amino acids. The transcript level of SpPIP1 was higher in the root of S. purpurea than in the flower, leaf and stem. The level of SpPIP1 transcript increased significantly when treated with drought treatment. Subcellular localization result showed that SpPIP1 was localized in the plasma membrane. Ectopic expression of SpPIP1 in Arabidopsis thaliana resulted in plants with higher tolerance to drought treatment. SpPIP1 of S. purpurea may mediate plant response to arid environments.

The disadvantages of being a hybrid during drought: A combined analysis of plant morphology, physiology and leaf proteome in maize

A comparative analysis of various parameters that characterize plant morphology, growth, water status, photosynthesis, cell damage, and antioxidative and osmoprotective systems together with an iTRAQ analysis of the leaf proteome was performed in two inbred lines of maize (Zea mays L.) differing in drought susceptibility and their reciprocal F1 hybrids. The aim of this study was to dissect the parent-hybrid relationships to better understand the mechanisms of the heterotic effect and its potential association with the stress response. The results clearly showed that the four examined genotypes have completely different strategies for coping with limited water availability and that the inherent properties of the F1 hybrids, i.e. positive heterosis in morphological parameters (or, more generally, a larger plant body) becomes a distinct disadvantage when the water supply is limited. However, although a greater loss of photosynthetic efficiency was an inherent disadvantage, the precise causes and consequences of the original predisposition towards faster growth and biomass accumulation differed even between reciprocal hybrids. Both maternal and paternal parents could be imitated by their progeny in some aspects of the drought response (e.g., the absence of general protein down-regulation, changes in the levels of some carbon fixation or other photosynthetic proteins). Nevertheless, other features (e.g., dehydrin or light-harvesting protein contents, reduced chloroplast proteosynthesis) were quite unique to a particular hybrid. Our study also confirmed that the strategy for leaving stomata open even when the water supply is limited (coupled to a smaller body size and some other physiological properties), observed in one of our inbred lines, is associated with drought-resistance not only during mild drought (as we showed previously) but also during more severe drought conditions.