Molecular characterization and comparative transcriptional analysis of LMW-m-type genes from wheat (Triticum aestivum L.) and Aegilops species.

Twelve new LMW-GS genes were characterized from bread wheat (Triticum aestivum L.) cultivar Zhongyou 9507 and five Aegilops species by AS-PCR. These genes belong to the LMW-m type and can be classified into two subclasses designated as 1 and 2, with the latter predominant in both wheat and related wild species. Genes in the two subclasses were significantly different from each other in SNPs and InDels variations. In comparison to subclass 1, the structural features of subclass 2 differs in possessing 21 amino acid residue substitutions, two fragment deletions (each with 7 amino acid residues), and a double-residue deletion and two fragment insertions (12 and 2-5 residues). Phylogenetic analysis revealed that the two subclasses were divergent at about 6.8 MYA, earlier than the divergence of C, M, N, S(s) and U genomes. The S(s) and B genomes displayed a very close relationship, whereas the C, M, N and U genomes appeared to be related to the D genome of bread wheat. The presently characterized genes ZyLMW-m1 and ZyLMW-m2 from Zhongyou 9507 were assigned to the D genome. Moreover, these genes were expressed successfully in Escherichia coli. Their transcriptional levels during grain developmental stages detected by quantitative real-time PCR (qRT-PCR) showed that both genes started to express at 5 days post-anthesis (DPA), reaching the maximum at 14 DPA after which their expressions decreased. Furthermore, the expression level of ZyLMW-m2 genes was much higher than that of ZyLMW-m1 during all grain developmental stages, suggesting that the expression efficiency of LMW-GS genes between the two subclasses was highly discrepant.