Potyviral genomes encode just 11 major
proteins and multifunctionality is associated with most of these
proteins at different stages of the
virus infection cycle. Some potyviral
proteins modulate
phytohormones and protein degradation pathways and have either pro- or anti-viral/insect vector functions. Our previous work demonstrated that the potyviral
protein 6K1 has an antagonistic effect on vectors when expressed transiently in host plants, suggesting plant defenses are regulated. However, to our knowledge the mechanisms of how 6K1 alters plant defenses and how 6K1 functions are regulated are still limited. Here we show that the 6K1 from Turnip mosaic virus (TuMV) reduces the abundance of transcripts related to
jasmonic acid biosynthesis and
cysteine protease inhibitors when expressed in Nicotiana benthamiana relative to controls. 6K1 stability increased when
cysteine protease activity was inhibited chemically, showing a mechanism to the rapid turnover of 6K1 when expressed in trans. Using RNAseq, qRT-PCR, and enzymatic assays, we demonstrate TuMV reprograms
plant protein degradation pathways on the transcriptional level and increases 6K1 stability at later stages in the
infection process. Moreover, we show 6K1 decreases plant
protease activity in infected plants and increases TuMV accumulation in systemic leaves compared to controls. These results suggest 6K1 has a pro-viral function in addition to the anti-insect vector function we observed previously. Although the host targets of 6K1 and the impacts of 6K1-induced changes in
protease activity on insect vectors are still unknown, this study enhances our understanding of the complex interactions occurring between plants, potyviruses, and vectors.