Genome-Wide Identification of the ASMT Gene Family and Expression Analysis of Wheat ASMTs Under Abiotic and Biotic Stress

Melatonin is an important stress-protective agent in plant growth. Methyltransferase (ASMT) is an important enzyme in the concluding phase of melatonin production in plants. In this study, we performed the genome-wide identification and functional investigation of the ASMT gene family in hexaploid wheat and 14 other plants. ASMT genes in 15 plants were identified by using HMM scanning against the proteomes derived from a single representative reference genome for each species. They were classified into three subfamilies I-III by constructing four types of phylogenetic trees (Neighbour-joining with p-distance model, Neighbour-joining with JTT model, Maximum likelihood, and Bayesian inference). Based on exon–intron structure and domain diagrams, a conserved structural pattern characterized by successive intron phases 1 and 0 (the “1-0” pattern) was found in ASMT genes during evolution. Collinear events analysis indicated that polyploidization and tandem duplication synergistically promote the expansion of T. aestivum ASMT members. Cis-acting element analysis revealed that numerous stress- and hormone-responsive motifs (such as ABRE and LTR) were present in ASMTs of wheat, suggesting a role for ASMTs in adaptive signal transduction. Transcriptome analysis revealed that specific T. aestivum ASMT genes were strongly responsive to stress; for instance, II_TraesCS2B02G041200 and II_TraesCS2B02G606200 were strongly upregulated under drought and salt stress, respectively. To independently confirm the stress responsiveness of these candidates in a different genetic background, we performed quantitative real-time PCR (qRT-PCR) on selected genes under drought and salt treatments. The result showed that the expression trends of transcriptome and qRT-PCR were almost the same, identifying these ASMT genes as strong stress-responsive candidates under drought and salt treatments. In this study, we performed identification, classification, evolution analysis and expression pattern analysis of ASMTs in wheat and 14 other plants. Our study will provide a framework for the targeted genetic improvement of melatonin-mediated stress resistance.