|Xuan Zhang, Kai Dong, Kai Xu. Barley stripe mosaic virus infection requires PKA-mediated phosphorylation of cb for suppression of both RNA silencing and the host cell death response. New Phytologist. DOI: 10.1111/nph.15065|
Barley stripe mosaic virus infection requires PKA-mediated phosphorylation of cb for suppression of both RNA silencing and the host cell death response
Xuan Zhang, Kai Dong, Kai Xu, Kun Zhang, Xuejiao Jin, Meng Yang, Yongliang Zhang, Xianbing Wang, Chenggui Han, Jialin Yu and Dawei Li
The Barley stripe mosaic virus (BSMV) cb protein is a viral suppressor of RNA silencing (VSR) and symptom determinant. However, it is unclear how post-translational modiﬁcation affects the different functions of cb.
Here, we demonstrate that cb is phosphorylated at Ser-96 by a PKA-like kinase in vivo and in vitro. Mutant viruses containing a nonphosphorylatable substitution (BSMVS96A or BSMVS96R) exhibited reduced viral accumulation in Nicotiana benthamiana due to transient induction of the cell death response that constrained the virus to necrotic areas. By contrast, a BSMVS96D mutant virus that mimics cb phosphorylation spread similarly to the wild-type virus.
Furthermore, the S96A mutant had reduced local and systemic cb VSR activity due to having compromised its binding activity to 21-bp dsRNA. However, overexpression of other VSRs in trans or in cis failed to rescue the necrosis induced by BSMVS96A, demonstrating that suppression of cell death by cb phosphorylation is functionally distinct from its RNA silencing suppressor activities.
These results provide new insights into the function of cb phosphorylation in regulating RNA silencing and the BSMV-induced host cell death response, and contribute to our understanding of how the virus optimizes the balance between viral replication and virus survival in the host plants during virus infection.