Cytosine methylation is a well recognized epigenetic mark. Here, 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 TaFLS1 (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.

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Broad phenotypic variations were induced in derivatives of an asymmetric somatic hybridization of bread wheat (Triticum aestivum) and tall wheatgrass (Thinopyrum ponticum Podp); however, how these variations occurred was unknown. We explored the nature of these variations by cytogenetic assays and DNA profiling techniques to characterize six genetically stable somatic introgression lines. Karyotyping results show the six lines similar to their wheat parent, but GISH analysis identified the presence of a number of short introgressed tall wheatgrass chromatin segments. DNA profiling revealed many genetic and epigenetic differences, including sequences deletions, altered regulation of gene expression, changed patterns of cytosine methylation, and the reactivation of retrotransposons. Phenotypic variations appear to result from altered repetitive sequences combined with the epigenetic regulation of gene expression and/or retrotransposon transposition. The extent of genetic and epigenetic variation due to the maintenance of parent wheat cells in tissue culture was assessed and shown to be considerably lower than had been induced in the introgression lines. Asymmetric somatic hybridization provides appropriate material to explore the nature of the genetic and epigenetic variations induced by genomic shock.KEYWORDS bread wheat; asymmetric somatic hybridization; introgression line; genomic shock, genetic and epigenetic alteration W ITH the world's population continuing to increase, achieving a sustainable mode of food production represents an ever-growing challenge. Plant breeding has narrowed the genetic base of many crop species, but as yet has had little impact on the genetic diversity present in their wild relatives. In principle, this diversity can be introgressed into crops via sexual hybridization and subsequent backcrossing. However, in practice, wild-crop manipulation has been severely restricted by difficulties in creating the initial sexual hybrid and by sterility issues in the early backcross generations (Xia 2009). Asymmetric somatic hybridization is a viable alternative to introgression, especially where wide crosses are not feasible. It has been successfully exploited in bread wheat to transfer chromosomal segments from a number of related species Xiang et al. 2003Xiang et al. , 2004Cheng et al. 2004;Zhou and Xia 2005;Xia 2009). More importantly, asymmetric somatic hybridization offers smaller alien chromatin introgression, thereby overcoming a significant problem in wheat sexual hybrids where the Ph1 gene prevents homeologous recombination (Griffiths et al. 2006).Newly synthesized allopolyploids have provided an opportunity to explore the nature of the genetic and epigenetic changes triggered by polyploidization (Song et al. 1995;Comai et al. 2000;Ozkan et al. 2001;Shaked et al. 2001;Madlung et al. 2002;Han et al. 2003;Ma et al. 2004;Wang et al. 2004a;Salmon et al. 2005;Tate et al. 2006;Bassene et al. 2010;Xu et al. 2014), although a few allopolyploids were not accompanied with such changes (Liu...

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