Drought-related Responses Research Articles

Regulation of drought-related responses in tomato plants by two classes of calcineurin B-like (SlCBL1/2) proteins

Calcineurin-B-like proteins (CBLs) are essential components of the calcium signaling network and act during plant's response to stress and normal conditions. A combined research strategy of in-silico analysis and gene silencing experiment was employed to investigate the role of different classes of CBLs in tomato (Solanum lycopersicum L.) during the response to drought stress. Two different classes of CBL genes, including SlCBL3-1, and SlCBL3-2, with the minimum and a maximum number of drought-responsive cis-elements, were selected and were targeted for transient gene silencing in tomato followed by the drought treatment. The effect of silencing events was evaluated by determining of further growth and physiological traits in plants under both control and drought stress conditions. The results showed that silencing of SlCBL3-1 significantly reduced shoot and root growth, relative water content (RWC), and the concentration of pigments while increased free radical accumulation, lipid peroxidation, and leakage from the cells. On the other hand, no antioxidant enzyme activity or proline induction was triggered in plants after SlCBL3-1 silencing. Some of these adverse events were more significantly enhanced when the silenced plants were exposed to drought stress. Overall, a significant role for SlCBL3-1 in the life cycle of plant suggested under both normal and stress conditions. The SlCBL3-2 silencing showed more efficient plants recovery from silencing or drought stress conditions. Therefore, SlCBL3-2 gene may act as a negative regulator under stress conditions. The results might provide new theoretical insight and genetic resources for developing resistant crops against environmental stresses.

Pathways and Network Based Analysis of Candidate Genes to Reveal Cross-Talk and Specificity in the Sorghum (Sorghum bicolor (L.) Moench) Responses to Drought and It's Co-occurring Stresses.

Drought alone or in combination with other stresses forms the major crop production constraint worldwide. Sorghum, one of the most important cereal crops is affected by drought alone or in combination with co-occurring stresses; notwithstanding, sorghum has evolved adaptive responses to combined stresses. Furthermore, an impressive number of sorghum genes have been investigated for drought tolerance. However, the molecular mechanism underling drought response remains poorly understood. We employed a systems biology approach to elucidate regulatory and broad functional features of these genes. Their interaction network would provide insight into understanding the molecular mechanisms of drought tolerance and underpinning signal pathways. Functional analysis was undertaken to determine significantly enriched genesets for pathways involved in drought tolerance. Analysis of distinct pathway cross-talk network was performed and drought-specific subnetwork was extracted. Investigation of various data sources such as gene expression, regulatory pathways, sorghumCyc, sorghum protein-protein interaction (PPI) and Gene Ontology (GO) revealed 14 major drought stress related hub genes (DSRhub genes). Significantly enriched genesets have shown association with various biological processes underlying drought-related responses. Key metabolic pathways were significantly enriched in the drought-related genes. Systematic analysis of pathways cross-talk and gene interaction network revealed major cross-talk pathway modules associated with drought tolerance. Further investigation of the major DSRhub genes revealed distinct regulatory genes such as ZEP, NCED, AAO, and MCSU and CYP707A1. These were involved in the regulation of ABA biosynthesis and signal transduction. Other protein families, namely, aldehyde and alcohol dehydrogenases, mitogene activated protein kinases (MAPKs), and Ribulose-1,5-biphosphate carboxylase (RuBisCO) were shown to be involved in the drought-related responses. This shows a diversity of complex functional features in sorghum to respond to various abiotic stresses. Finally, we constructed a drought-specific subnetwork, characterized by unique candidate genes that were associated with DSRhub genes. According to our knowledge, this is the first in sorghum drought investigation that introduces pathway and network-based candidate gene approach for analysis of drought tolerance. We provide novel information about pathways cross-talk and signaling networks used in further systems level analysis for understanding the molecular mechanism behind drought tolerance and can, therefore, be adapted to other model and non-model crops.

Physiological and Proteomic Analysis of the Rice Mutant cpm2 Suggests a Negative Regulatory Role of Jasmonic Acid in Drought Tolerance.

It is widely known that numerous adaptive responses of drought-stressed plants are stimulated by chemical messengers known as phytohormones. Jasmonic acid (JA) is one such phytohormone. But there are very few reports revealing its direct implication in drought related responses or its cross-talk with other phytohormones. In this study, we compared the morpho-physiological traits and the root proteome of a wild type (WT) rice plant with its JA biosynthesis mutant coleoptile photomorphogenesis 2 (cpm2), disrupted in the allene oxide cyclase (AOC) gene, for insights into the role of JA under drought. The mutant had higher stomatal conductance, higher water use efficiency and higher shoot ABA levels under severe drought as compared to the WT. Notably, roots of cpm2 were better developed compared to the WT under both, control and drought stress conditions. Root proteome was analyzed using the Tandem Mass Tag strategy to better understand this difference at the molecular level. Expectedly, AOC was unique but notably highly abundant under drought in the WT. Identification of other differentially abundant proteins (DAPs) suggested increased energy metabolism (i.e., increased mobilization of resources) and reactive oxygen species scavenging in cpm2 under drought. Additionally, various proteins involved in secondary metabolism, cell growth and cell wall synthesis were also more abundant in cpm2 roots. Proteome-guided transcript, metabolite, and histological analyses provided further insights into the favorable adaptations and responses, most likely orchestrated by the lack of JA, in the cpm2 roots. Our results in cpm2 are discussed in the light of JA crosstalk to other phytohormones. These results together pave the path for understanding the precise role of JA during drought stress in rice.

A metabolomic study in oats (Avena sativa) highlights a drought tolerance mechanism based upon salicylate signalling pathways and the modulation of carbon, antioxidant and photo-oxidative metabolism.

Although a wealth of information is available on the induction of one or several drought-related responses in different species, little is known of how their timing, modulation and crucially integration influence drought tolerance. Based upon metabolomic changes in oat (Avena sativa L.), we have defined key processes involved in drought tolerance. During a time course of increasing water deficit, metabolites from leaf samples were profiled using direct infusion-electrospray mass spectroscopy (DI-ESI-MS) and high-performance liquid chromatography (HPLC) ESI-MS/MS and analysed using principal component analysis (PCA) and discriminant function analysis (DFA). The involvement of metabolite pathways was confirmed through targeted assays of key metabolites and physiological experiments. We demonstrate an early accumulation of salicylic acid (SA) influencing stomatal opening, photorespiration and antioxidant defences before any change in the relative water content. These changes are likely to maintain plant water status, with any photoinhibitory effect being counteracted by an efficient antioxidant capacity, thereby representing an integrated mechanism of drought tolerance in oats. We also discuss these changes in relation to those engaged at later points, consequence of the different water status in susceptible and resistant genotypes.

Leaf responses to mild drought stress in natural variants of Arabidopsis.

Although the response of plants exposed to severe drought stress has been studied extensively, little is known about how plants adapt their growth under mild drought stress conditions. Here, we analyzed the leaf and rosette growth response of six Arabidopsis (Arabidopsis thaliana) accessions originating from different geographic regions when exposed to mild drought stress. The automated phenotyping platform WIWAM was used to impose stress early during leaf development, when the third leaf emerges from the shoot apical meristem. Analysis of growth-related phenotypes showed differences in leaf development between the accessions. In all six accessions, mild drought stress reduced both leaf pavement cell area and number without affecting the stomatal index. Genome-wide transcriptome analysis (using RNA sequencing) of early developing leaf tissue identified 354 genes differentially expressed under mild drought stress in the six accessions. Our results indicate the existence of a robust response over different genetic backgrounds to mild drought stress in developing leaves. The processes involved in the overall mild drought stress response comprised abscisic acid signaling, proline metabolism, and cell wall adjustments. In addition to these known severe drought-related responses, 87 genes were found to be specific for the response of young developing leaves to mild drought stress.

Use of DArT molecular markers for QTL analysis of drought-stress responses in soybean. II. Marker identification and QTL analyses

This study applied newly developed Diversity Arrays Technology (DArT) and soybean and mungbean DArT libraries for quantitative trait locus (QTL) linkage analysis in recombinant inbred lines (RILs) from three soybean crosses that had previously been assessed for physiological response to severe drought stress. The phenotypic assessments had identified statistically significant genetic variation among and within the RIL populations and their parents for three drought-related responses: epidermal conductance (ge) and relative water content (RWC) during stress, and plant recovery after stress. The new linkage maps containing only DArT markers for the three populations individually contained 196–409 markers and 15–22 linkage groups (LGs), with an aggregate length ranging from 409.4 to 516.7 cM. An integrated map constructed by using the marker data from all three RIL populations comprised 759 DArT markers, 27 LGs and an expanded length of 762.2 cM. Two populations with the landrace accession G2120 as a parent, CPI 26671 × G2120 (CG) and Valder × G2120 (VG), respectively contained 106 and 34 QTLs. In each of these populations, 10 LGs harboured QTLs associated with RWC, ge and recovery ability, of which six similar LGs were associated with drought tolerance. A BLAST (Basic Local Alignment Search Tool) search for sequences of 19 selected DArT markers linked to QTLs conditioning the drought-response traits indicated that 18 DArT markers were unique and aligned to 12 soybean chromosomes. Comparison of these sequenced DArT markers with other markers associated with drought-related QTLs in previously reported studies using other marker types confirmed that five of them overlapped, whereas the remaining 13 were new. Except for chromosome 15, the chromosomes with which the DArT QTLs in the CG and VG populations were associated were those that had been shown to harbour drought-related QTLs in previous studies. A BLASTx protein database search identified soPt-856602 as being associated with the gene for a probable glycosyltransferase At5g03795-like isoform X1 on chromosome 6. Although the several QTLs identified in the study were all of relatively minor effect, it was concluded that, because the DArT technology involves large numbers of markers and enables many lines to be genotyped simultaneously, it should help the process of manipulating multiple QTLs and so enhance their likely cumulative effect.

Isolation and characterization of drought-responsive genes from peanut roots by suppression subtractive hybridization

article i nfo Background: Peanut (Arachis hypogaea L.) is an important economic and oilseed crop. Long-term rainless conditions and seasonal droughts can limit peanut yields and were conducive to preharvest aflatoxin contamination. To elucidate the molecular mechanisms by which peanut responds and adapts to water limited conditions, we isolated and characterized several drought-induced genes from peanut roots using a suppression subtractive hybridization (SSH) technique. Results:RNAwasextractedfrompeanutroots subjectedtoa waterstress treatment(45% fieldcapacity)andfrom control plants (75% field capacity), and used to generate an SSH cDNA library. A total of 111 non-redundant sequences were obtained, with 80 unique transcripts showing homology to known genes and 31 clones with no similarity to either hypothetical or known proteins. GO and KEGG analyses of these differentially expressed ESTs indicated that drought-related responses in peanut could mainly be attributed to genes involved in cellular structure and metabolism. In addition, we examined the expression patterns of seven differentially expressed candidate genes using real-time reverse transcription-PCR (qRT-PCR) and confirmed that all were up-regulated in roots in response to drought stress, but to differing extents. Conclusions: We successfully constructed an SSH cDNA library in peanut roots and identified several drought-related genes. Our results serve as a foundation for future studies into the elucidation of the drought stress response mechanisms of peanut.

Whole-Genome Mapping of Agronomic and Metabolic Traits to Identify Novel Quantitative Trait Loci in Bread Wheat Grown in a Water-Limited Environment

Drought is a major environmental constraint responsible for grain yield losses of bread wheat (Triticum aestivum) in many parts of the world. Progress in breeding to improve complex multigene traits, such as drought stress tolerance, has been limited by high sensitivity to environmental factors, low trait heritability, and the complexity and size of the hexaploid wheat genome. In order to obtain further insight into genetic factors that affect yield under drought, we measured the abundance of 205 metabolites in flag leaf tissue sampled from plants of 179 cv Excalibur/Kukri F1-derived doubled haploid lines of wheat grown in a field experiment that experienced terminal drought stress. Additionally, data on 29 agronomic traits that had been assessed in the same field experiment were used. A linear mixed model was used to partition and account for nongenetic and genetic sources of variation, and quantitative trait locus analysis was used to estimate the genomic positions and effects of individual quantitative trait loci. Comparison of the agronomic and metabolic trait variation uncovered novel correlations between some agronomic traits and the levels of certain primary metabolites, including metabolites with either positive or negative associations with plant maturity-related or grain yield-related traits. Our analyses demonstrate that specific regions of the wheat genome that affect agronomic traits also have distinct effects on specific combinations of metabolites. This approach proved valuable for identifying novel biomarkers for the performance of wheat under drought and could facilitate the identification of candidate genes involved in drought-related responses in bread wheat.

Drought-Related Responses of Aquatic Turtle Populations

A major drought in South Carolina provided opportunity to observe certain repro- ductive and emigration responses of freshwater turtle populations that have been studied for 15 years. Five species responded differentially to the drying of a major aquatic habitat. Pseudemys scripta and P. floridana emigrated in greater numbers, and fewer females laid eggs than in any previous year. Sternotherus odoratus and Deirochelys reticularia did not reproduce at the level of previous years but did not abandon the aquatic habitat. Reproduction and emigration of Kinoster- non subrubrum were not appreciably different from other years. The differing responses of the species are discussed in terms of the ecological and evolutionary differences between them.