The hypervariable N-terminal of soybean mosaic virus P1 protein influences its pathogenicity and host defense responses

Abstract

Soybean mosaic virus (SMV; Potyvirus, Potyviridae) is one of the most prevalent and destructive viral pathogens in the world. The P1 protein is the first N-terminal product in the potyvirus genome and shows a high sequence variability that may be related to virus adaptation to hosts. In this work, we focused on the different functions of P1 proteins in two SMV isolates SMVGZL and SMVNB during their infection of plants. Isolate SMVGZL induced weaker symptoms than SMVNB in mechanical inoculation assays, and the accumulation level of SMV CP in SMVGZL-infected leaves was lower than that in leaves infected with SMVNB, especially at the late stage of infection. The isolates SMVGZL and SMVNB had a high similarity in genome sequence except for the P1 region. P1GZL induced a higher salicylic acid (SA) response than P1NB in Nicotiana benthamiana, which may explain the lower virus titers in plants infected with SMVGZL. Our results suggest that the divergence in the P1 proteins of these SMV isolates influenced their virulence via differentially regulating SA signaling.