Multiple-level regulation of a plant sterol methyltransferase during rice stripe virus infection.

The plant sterol biosynthesis pathway is essential for normal plant growth and development, but its role in plant-virus interactions remains poorly understood. In this study, we investigated the regulation of sterol methyltransferase 2 (SMT2), a key enzyme of the plant sterol biosynthesis pathway, during rice stripe virus (RSV) infection. Our findings demonstrate that Nicotiana benthamiana SMT2 (NbSMT2) is transcriptionally upregulated during RSV infection. Together with sterol 4α-methyl oxidase 2 and sterol Δ(7)-reductase, two other enzymes in the sterol biosynthesis pathway, NbSMT2 positively regulates the cell-to-cell mobility of the RSV movement protein pc4, thus facilitating viral spread. However, the accumulation of reactive oxygen species in response to RSV infection promotes the polyubiquitination and degradation of NbSMT2, contributing to RSV resistance. NbSMT2 also forms aggregates through intermolecular disulfide bonds, limiting its degradation and maintaining its protein pool. N. benthamiana thus appears to balance normal growth and development with antiviral responses through multiple regulatory mechanisms targeting NbSMT2.