Thermotolerance In Wheat Research Articles

Calcium triggers protein kinases-induced signal transduction for augmenting the thermotolerance of developing wheat (Triticum aestivum) grain under the heat stress

Calcium acts as a signaling molecule and plays very important role in plants-tolerance to the abiotic stresses including the heat stress. We studied the effect of exogenous Ca2+ (10 mM) prior to the heat stress (42 °C, 2 h) on different molecular and biochemical parameters associated with thermotolerance in wheat (Triticum aestivum). We could observe 64 and 52 unique protein spots in HD2967 (thermotolerant) and HD2329 (thermosusceptible) cultivars under normal and heat stress condition. Similarly, 13 and 9 (HD2967) and 19 and 9 proteins (HD2329) were observed to be up-regulated and down-regulated in response to HS. MALDI-TOF-TOF/MS characterization identified the differentially expressed protein (DEP) spots as calcium dependent protein kinase (CDPK), oxygen evolving enhancer protein, HSP17, HSP70, Rubisco activase etc. Transcript profiling of identified stress-associated genes (SAGs) showed very high expression of CDPK, HSFA4a, HSP17, SOD and APX in response to Ca2+ + HS in HD2967 compared to HD2329 cultivars of wheat. Similarly accumulation of signaling molecules (H2O2 and CDPK) as well as osmolyte was observed maximum in response to Ca2+ + HS in HD2967 compared to HD2329 cultivars. Very high activities of guaiacol-peroxidase and ascorbate peroxidase were observed in Ca-treated HD2967 compared to HD2329 when exposed to HS. It is the abundance of these chaperones and antioxidant enzymes in thermotolerant cultivar which limit the accumulation of H2O2 in response to Ca2+ and HS. Exogenous Ca2+ application showed negative correlation with lipid peroxidation and positive correlation with total antioxidant capacity of the cell system under the elevated temperature. Alteration in Ca2+ efflux triggers the activities of kinases and peroxidases more in tolerant compared to susceptible cultivars which regulate the accumulation of ROS inside the cell and attenuate the lipid peroxidation process. Ultimately, it enhances the total antioxidant capacity and thermotolerance of the plants under the heat stress.

Molecular Marker analysis Reveals Genetic Diversity among Wheat(Triticum aestivumL. em. Thell) Genotypes varying for Thermo-Tolerance

High temperature stress limits wheat production worldwide. Several studies reflect that genotypic variability exists for thermo-tolerance in wheat. In this study, genotypic varia-bility for thermo-tolerance was dissected at mo-lecular level. We accessed 20 selected bread wheat genotypes (10 thermo-tolerant and 10 thermo-sensitive) for genetic diversity analysis using random amplified polymorphic DNA (RAPD) and inter simple sequence repeats (ISSR) markers. In RAPD analysis, a total of 126 alleles were detected using 18 primers, among which 76 alleles (60.3%) were polymorphic. In ISSR analy-sis, using a total of 11 ISSR primers, 95 am-plified bands were obtained of which 46 (48.4%) were polymorphic. The average num-ber of polymorphic bands was higher in case of RAPDs (4.22) as compared to that in ISSRs (4.18). The clustering dendrogram generated by ISSR based similarity matrix, segregated thermo-tolerant and thermo-sensitive genotypes better than the RAPD based clustering dendrogram. One of ISSR primers (ISSR-41) amplified a ≈2800 bp band which was able to distinguish all the thermo-tolerant and sensitive genotypes except one. This marker identified in the study may po-tentially be used in marker assisted selection to develop thermo-tolerant wheat varieties.

Association of SSCP variants of HSP genes with physiological and yield traits under heat stress in wheat

Heat stress alters various physiological phenomenons which adversely affect yield components and ultimately lead to a severe reduction in economic yield in wheat (Triticum aestivum L.). To cope with heat stress, plants have army of heat shock proteins (HSPs) which acts as molecular chaperones stabilizing the polypeptides and membranes. The thermo-tolerance ability of different genotypes of a plant species resides in their genetic diversity of HSP genes. In this study, association of HSPs with physiological and yield traits under heat stress was investigated. Results showed that wheat genotypes differed significantly in their response to high temperature. Single-strand conformation polymorphism (SSCP) analysis of targeted coding sequence of different HSP genes produced seven different haplotypes from HSP 16.9, while only two haplotypes were produced from HSP 23.5, HSP 90a and HSP 90b. Among 25 SSCP variants detected in HSP 16.9 targeted coding sequence, 12 were polymorphic and three of them were found significantly associated with canopy temperature (CT), relative water content (RWC), thousand grain weight (TGW) and normalized difference vegetation index (NDVI). These associated alleles explained 11.4 to 32.9% of the variation for individual trait. The association between HSP variants and these traits may provide new insight for HSPs potential contribution to thermo-tolerance which can be used for improvement of thermo-tolerance in wheat through marker assisted selection.

Novel and conserved heat-responsive microRNAs in wheat (Triticum aestivum L.).

MicroRNAs (miRNAs) are small endogenous RNAs of ~22 nucleotides that have been shown to play regulatory role by negatively affecting the expression of genes at the post-transcriptional level. Information of miRNAs on some important crops like soybean, Arabidopsis, and rice, etc. are available, but no study on heat-responsive novel miRNAs has yet been reported in wheat (Triticum aestivum L.). In the present investigation, a popular wheat cultivar HD2985 was used in small RNA library construction and Illumina HiSeq 2000 was used to perform high-throughput sequencing of the library after cluster generation; 110,896,604 and 87,743,861 reads were generated in the control (22 °C) and heat-treated (42 °C for 2 h) samples, respectively. Forty-four precursor and mature miRNAs were found in T. aestivum from miRBase v 19. The frequencies of the miRNA families varied from 2 (tae-miR1117) to 60,672 (tae-miR159b). We identify 1052 and 902 mature miRNA sequences in HD2985 control and HS-treated samples by mapping on reference draft genome of T. aestivum. Maximum identified miRNAs were located on IWGSC_CSS_3B_scaff (chromosome 3B). We could identify 53 and 46 mature miRNA in the control and HS samples and more than 516 target genes by mapping on the reference genome of Oryza sativa, Zea mays, and Sorghum bicolor. Using different pipelines and plant-specific criteria, 37 novel miRNAs were identified in the control and treated samples. Six novel miRNA were validated using qRT-PCR to be heat-responsive. A negative correlation was, however, observed between the expression of novel miRNAs and their targets. Target prediction and pathway analysis revealed their involvement in the heat stress tolerance. These novel miRNAs are new additions to miRNA database of wheat, and the regulatory network will be made use of in deciphering the mechanism of thermotolerance in wheat.

Wheat cellular thermotolerance is related to yield under heat stress

Cellular thermotolerance in terms of cellular membrane thermostability is often implied as an indication of crop heat tolerance and it is therefore considered as a possible selection criterion for heat tolerance. While there is ample genetic variability for cellular thermotolerance in wheat and other crop plants its relations to yield under heat stress is not sufficiently established. This study was performed to assess the genetic relations in wheat between cellular thermotolerance and yield under heat stress. In one study the co-segregation among cellular membrane thermostability (CMS), yield under chronic heat stress and yield under non-stress conditions was evaluated in a random inbred line (RIL) population of a cross between heat resistant (Danbata) and heat susceptible (Nacozari) cultivars. In a second study the same association was evaluated for yield under heat stress in 49 F7 breeding lines randomly selected from a breeding program. CMS was assayed in growth chamber grown and heat-hardened seedlings. Yield was evaluated under Mediterranean summer irrigated conditions where chronic heat stress caused a reduction in mean yield of the RIL population by 47% as compared with the normal winter growing conditions (non-stress). The RILs varied significantly (p<0.05) for CMS, biomass and yield under stress and non-stress conditions. The two parent cultivars did not differ in biomass or yield under non-stress (winter) conditions but they widely differed for both traits under heat stress. Yield of RILs under heat stress was well distributed between the extreme values of the parent cultivars. There was a significant RIL by season interaction for biomass (F = 9.74; p<0.0001) and yield (F = 10.08; p<0.0001), indicating specific adaptation to heat stress of certain lines in terms of their productivity. Broad-sense heritability for yield was high and nearly the same in the winter (h 2=0.71)and the summer (h 2=0.67). Broad-sense heritability for CMS was high (h 2=0.74). CMS was positively and significantly (p<0.01) correlated across 98 RILs with biomass (r = 0.60* *) and yield (r = 0.53**) under stress but rot with biomass or yield under non-stress conditions. The 49 breeding lines varied significantly (p<0.01) for CMS and yield under chronic heat stress in the summer season. CMS and yield were significantly correlated (r = 0.56**) across lines. Overall the associations between CMS and yield under heat stress were reasonably strong and significant but not perfect. Other factors besides cellular thermostability may support yield under heat stress. CMS alone cannot be used as the exclusive selection criterion for heat tolerance in wheat breeding. lt may be valuable as a supplemental criterion in the final breeding stages or as a rough selection tool to reduce a large population into the most likely heat tolerant core at the early stages of the breeding program.

Expression of a unique plastid-localized heat-shock protein is genetically linked to acquired thermotolerance in wheat

We have used a combination of molecular and classical genetic approaches to delineate the relationship between a specific HSP member and cell viability under heat stress. Using recombinant inbred lines (RILs) of wheat, derived from a cross of the thermotolerant cultivar ‘Mustang’ and the thermosusceptible cultivar ‘Sturdy,’ we have identified a unique HSP and a differentially expressed cDNA sequence, both related to the plastid-localized HSP26 gene family, that are closely associated with acquired thermotolerance in wheat. An isoform of HSP26 was synthesized under heat stress in all examined thermotolerant RILs and ‘Mustang’, and was absent in all examined thermosusceptible RILs and ‘Sturdy.’ Using a modified differential-display method, we have also identified a gene-specific cDNA sequence that is similar to other known members of the wheat HSP26 gene family and is selectively expressed in ‘Mustang’ and most of the examined thermotolerant RILs, but not expressed in ‘Sturdy’ and all the thermosusceptible RILs. These results suggest a genetic linkage between the acquired thermotolerance trait and the differential expression of a unique member of the HSP26 gene family.