The betaflexivirus Carlavirus vignae recruits N-acetylserotonin O-methyltransferase 8 (GmASMT8) during its replication in soybean

Identification of host factors is an important step towards understanding viral infection. Host factors involved in the replication of betaflexiviruses remain largely unknown. Here, we identify the soybean N-acetylserotonin O-methyltransferase GmASMT8 as a host factor required for efficient replication of cowpea mild mottle virus (CPMMV; Carlavirus vignae ). GmASMT8 was identified in a yeast two-hybrid screen using a soybean cDNA library and shown to interact with the viral RNA-dependent RNA polymerase (RdRp) domain by yeast two-hybrid and bimolecular fluorescence complementation assays. Subcellular localization analyses revealed that GmASMT8 localizes to the cytoplasm, whereas the CPMMV RdRp domain forms ER-associated punctate structures consistent with potential replication sites. GmASMT8 expression was induced during CPMMV infection, and gain- and loss-of-function analyses demonstrated that GmASMT8 positively regulates viral accumulation. Overexpression of GmASMT8 in soybean protoplasts enhanced CPMMV accumulation, whereas virus-induced gene silencing markedly reduced viral accumulation in soybean plants. Together, these results suggest that GmASMT8 plays a critical role throughout the infection process and is required for RNA CPMMV multiplication. This study represents the first report of a host protein interacting with the RdRp domain of a Betaflexiviridae .