The Effect Of DNA Methylation On Salinity Stress-responsive Genes In Wheat

Serving as one of the most important staple crops globally, bread wheat (Triticum aestivum L.) provides calories for approximately 30% world population. Attention in wheat has been increasingly paid to abiotic stress in the past few years, owing to climate change, loss of arable land due to growing urbanization and environmental degradation caused by pollution. Soil salinity is the major constraint on wheat grain yield worldwide.Cytosine methylation is a well recognized epigenetic mark. DNA methylation is thought to influence a wide range of biological processes, and some aspects of gene expression during abiotic stress episodes have been shown to be affected by differential methylation.The bread wheat cultivar SR3 is a high yielding, salinity-tolerant derivative of an asymmetric somatic hybrid between a salinity-sensitive cultivar Jinan 177 (JN177) and salt-resistant tall wheatgrass (Thinopyrum ponticum) which has proven phenotypically and cytogenetically stable over many selfing generations. The DNA methylation status was scanned both in SR3 and JN177, which gave a conclusion that the expressions of salinity stress-responsive genes were correlated with the DNA methylation status of their putative promoter regions in hexaploid wheat. The genetic shock caused by the asymmetric somatic hybrid led to a reprogramming of DNA methylation between JN177 and SR3, which somehow contributed to the salinity tolerance of SR3. Five wheat salinity stress-responsive genes of which the expressions were regulated by DNA methylation were identified and functional analyzed preliminary through hetero-expression in Arabidopsis and over-expression in wheat. Moreover, the evolutionary fates of HKT1;5 homoeologs including genetic and epigenetic variation, expression pattern, protein function, and the relationship between homoeologs were elaborated.1 Induced and constitutive DNA methylation in a salinity-tolerant wheat introgression lineHere, the methylation status of a salinity-tolerant wheat cultivar (cv. SR3, derived from a somatic hybridization event) and its progenitor parent (cv. JN177) was explored both globally and within a set of 24 genes responsive to salinity stress. A further comparison was made between DNA extracted from plants grown under control conditions and when challenged by salinity stress. The SR3 and JN177 genomes differed with respect to their global methylation level, and methylation levels were reduced by exposure to salinity stress. We found the genetic stress-(triggered by a combination of different genomes in somatic hybridization) induced methylation pattern of 13 loci in non-stressed SR3; the same 13 loci were found to undergo methylation in salinity-stressed JN177. For the salinity-responsive genes, SR3 and JN177 also showed different methylation modifications. C methylation polymorphisms induced by salinity stress were present in both the promoter and coding regions of some of the 24 selected genes, but only the former were associated with changes in transcript abundance. The expression of both TaFLSl (encoding a flavonol synthase) and TaWRSI5 (encoding a Bowman-Birk-type protease inhibitor), which showed both a different expression and a different DNA methylation level between SR3 and JN177, enhanced the salinity tolerance of Arabidopsis thaliana. C methylation changes appear to be a common component of the plant response to stress, and methylation changes triggered by somatic hybridization may contribute to the superior salinity tolerance of SR3.2 The identification and preliminary functional analysis of a wheat salinity stress-responsive gene, TαCYP81During the DNA methylation scanning of first section, TaCYP81 was discovered to be expressed divergently under salt stress between SR3 and JN177, which proved to be involved in the different status of DNA methylation. Furthermore, the protein of TaCYP81 was recruited to the outer-membrane of endoplasmic reticulum strongly under salt stress by sub-cellular localization analysis. TaCYP81 was hetero-expressed in Arabidopsis and over-expressed in wheat. Phenotype assay showed that TaCYP81 could enhance the salinity tolerance both in Arabidopsis and in wheat. Besides, TaCYP81 could alleviate the H2O2 in Arabidopsis, which was coincided with that TaCYP81 could accelerate the ROS scavenging activity in Arabidopsis.3 Genetic and epigenetic variation among the wheat HKT1;5 homeologsPlants adapted to saline soils have evolved the capacity to translocate sodium (Na+) ions from the root to the shoot. The wheat genes TmHKT1;5-A and TaHKT1;5-D, which both encode an Na+selective transporter, have been shown to be synonymous with the two salinity tolerance genes Nax2 and Knal, respectively. Here, it has been shown that in hexaploid wheat, the abundance of two of the three B genome HKT1;5 transcripts (-B1 and-B2) was much less than that of HKT1;5-D. HKT1;5-B3 appeared to be a pseudogene in both tetraploid and hexaploid wheat. By comparing the behavior of the copies present in Aegilops speltoides (a species closely related to the progenitor of the B genome), the suppression of HKT1;5-B1 transcription at the higher ploidy levels was shown to be regulated by DNA methylation, while that of HKT1;5-B2 was due to the insertion of repetitive elements into its promoter. A functional analysis based on protein structure comparisons and growth inhibition assays in transgenic yeast cells indicated that HKT1;5-B1 is a functional Na+ transporter. The salinity tolerance of tetraploid wheat was raised when HKT1;5-B1 was activated by exposure to the DNA methyltransferase inhibitor 5-azaC. Our study will give a new insight into the divergently evolutionary fate of HKT1;5 homoeologs in wheat.