Soybean mosaic virus helper component-protease enhances somatic embryo production and stabilizes transgene expression in soybean.

Soybean mosaic virus (SMV) helper component protease (HC-Pro), a suppressor of post-transcriptional gene silencing, was evaluated for its ability to enhance production of soybean hygromycin-resistant somatic embryos (HR-SEs), and stabilize transgene expression. Immature soybean cotyledonary explants were co-cultured with Agrobacterium tumefaciens strain KYRT1 harboring either pCAMBIA1302, carrying a hygromycin phosphotransferase gene (hpt) and a gene encoding green fluorescent protein; pCAMBIA1305.1, carrying hpt and beta-glucuronidase (uidA) genes; pG2-HC-Pro, a derivative of pCAMBIA1305.1 containing SMV G2 HC-Pro; or pG5-HC-Pro, a derivative of pCAMBIA1305.1 containing SMV G5 HC-Pro, but lacking uidA. Significantly (rho<0.02) higher numbers of HR-SEs were obtained from explants transformed with Agrobacterium harboring either pG2-HC-Pro or pG5-HC-Pro than with either of the vector controls (pCAMBIA1302 or pCAMBIA1305.1). Beta-glucuronidase (GUS) expression was significantly (rho<0.003) higher in 50-day-old transgenic plants expressing GUS along with SMV-HC-Pro and in SMV-infected GUS transgenic plants than in transgenic plants expressing GUS alone. Together, these data suggest that SMV-HC-Pro enhanced recovery of HR-SEs by suppressing silencing of the hygromycin phosphotransferase gene.