Expression divergence of TaMBD2 homoeologous genes encoding methyl CpG-binding domain proteins in wheat (Triticum aestivum L.).

Most hexaploid wheat genes are present as triplicate homoeologs derived from the ancestral species. Previously, we isolated six wheat cDNAs with open reading frame, encoding methyl CpG-binding domain proteins (MBDs). In this study, the genomic and cDNA sequences of three TaMBD2 homoeologous genes were obtained and mapped on chromosomes 5A, 5B and 5D, respectively. These sequences showed a very high conservation in the coding region and the exon/intron structure, but the cDNA sequences are distinguishable by a 9-bp insertion in coding region and a size polymorphism in the 3'-untranslated region (UTR). The expression patterns of each homeologous gene in different tissues of various developmental stages and in response to abiotic stress were analyzed by using real-time PCR. Relative mRNA abundance of the three homoeologs varied considerably in different developmental stages from seedling to developing seeds. Most notably, TaMBD2-5B and TaMBD2-5D were highly responsive to salt stress and TaMBD2-5B was specifically upregulated by low temperature in the seedling leaves. These results provide further evidence for the expression variation of genes duplicated in allopolyploids. Moreover, the variation of TaMBD2 homoeologous gene expression in response to environmental stress may enable plants to better cope with stresses in their natural environments.