Comprehensive Analysis of the DNA Methyltransferase Genes and Their Association with Salt Response in Pyrus betulaefolia

Abstract

DNA methylation plays an indispensable role in genome stability, regulation of gene expression and plant stress response. It is mediated by DNA methyltransferases (MTases). Twelve putative MTases of P. betulaefolia were identified and were classified into MET1, CMT, DRM2 and Dnmt2 groups based on the organization of various characteristic domains. Three pairs of paralogous genes were identified with the Ka/Ks ratio varied from 0.232 for PbeMET1a and PbeMET1b to 0.251 for PbeCMT2 and PbeCMT3, respectively. In addition, the Ka/Ks ratio for nine pairs of orthologous gene pairs between P. betulaefolia and apple were varied from 0.053 for PbeDRM3 and MD17G1031900 to 0.278 for PbeDnmt2b and MD15G1120500, respectively. All the 12 members of MTase genes were located on nine chromosomes out of 17 P. betulaefolia chromosomes with highly conserved protein sequence structures. The isoelectric points (pI) of MTases ranged from 4.74 to 7.24, while molecular weight varied from 35.99 to 174.32. The expression profiles of MTase and other salt-responsive genes under salt stress treatment revealed their important roles involved in salt response in P. betulaefolia. Furthermore, three selected salt-responsive genes (PbeNHX2.1, PbeCBL2 and PbeAKT2) were found altered in methylation level of promoters (which contain CpG islands) under salt stress. Especially, the PbeAKT2 promoter regions showed high CHG and CHH methylation types. Our study provided a genome-wide survey of the MTase gene family and highlighted their roles in salt response. These results also provided an effective way for the breeding and improvement of salt-tolerant pear varieties.