N6-methyladenosine (m6A) modification, as an important post-transcriptional regulator, is the most prevalent RNA modification in eukaryotes. However, the biological role of m6A in oomycetes remains unclear. Here, we characterized three m6A methyltransferases PsMETTL3A, PsMETTL3B, and PsMETTL16 that mainly affected the m6A levels in the CDS and 3’UTR in Phytophthora sojae. They play an important role in production of sporangia and oospores, mycelial growth, and virulence. PsMETTL3A/3B/16-mediated m6A positively regulated mRNA stability and translation efficiency of genes involved in chromatin remodeling and epigenetic regulation. Interestingly, PsMETTL3A, PsMETTL3B, or PsMETTL16 function in “independent” and “overlap” synergetic pattern. PsMETTL16 could interact with PsMETTL3A and PsMETTL3B to mediate m6A on some of the transcripts. Moreover, PsMETTL3A and PsMETTL3B positively regulated the expression of PsMETTL16 in an m6A-dependent manner. More importantly, m6A-modified PsBdf1 regulate chromatin accessibility to maintain DNA damage repair and tolerate host ROS stress in a PsMETTL3A/3B/16-dependent manner. Overall, these results indicate that m6A-mediated RNA metabolism are associated with development and pathogenicity of P. sojae, highlighting epigenetic variation as a mechanism of plant pathogenic oomycetes adaptive plasticity.
Overall design: We identified three major m6A methyltransferases PsMETTL3A, PsMETTL3B, and PsMETTL16 in Phytophthora sojae, and obtained their knockout mutants, respectively, in order to further analyze whether the downstream m6A modification mediated by different methyltransferases is different. We performed MERIP (m6A) -seq of the wild type P6497 of Phytophthora sojae and the three methyltransferase knockout mutants mentioned above.
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