Inhibition of the host proteasome facilitates papaya ringspot virus accumulation and proteosomal catalytic activity is modulated by viral factor HcPro.

The ubiquitin/26S proteasome system plays an essential role not only in maintaining protein turnover, but also in regulating many other plant responses, including plant-pathogen interactions. Previous studies highlighted different roles of the 20S proteasome in plant defense during virus infection, either indirectly through viral suppressor-mediated degradation of Argonaute proteins, affecting the RNA interference pathway, or directly through modulation of the proteolytic and RNase activity of the 20S proteasome, a component of the 20S proteasome, by viral proteins, affecting the levels of viral proteins and RNAs. Here we show that MG132, a cell permeable proteasomal inhibitor, caused an increase in papaya ringspot virus (PRSV) accumulation in its natural host papaya (Carica papaya).

A single amino acid in the helicase domain of PMMoV-S is responsible for its enhanced accumulation in C. chinense (L(3)L(3)) plants at 32°C.

In Capsicum chinense (L(3)L(3)) plants a higher accumulation of the tobamovirus Pepper mild mottle virus strain S (PMMoV-S) as compared to the Italian strain PMMoV-I is detected when plants are grown at 32°C. By using a reverse genetic approach, we have established that a single amino acid at position 898 in the helicase domain of the polymerase protein, outside of the conserved regions of the helicase, is critical for the higher accumulation of PMMoV-S observed. It also is necessary for both increased accumulation of viral RNA of both polarities in pepper protoplasts and enhanced cell-to-cell movement in C.