Barley stripe mosaic virus infection requires PKA-mediated phosphorylation of γb for suppression of both RNA silencing and the host cell death response

New Phytol. 2018 Jun;218(4):1570-1585. doi: 10.1111/nph.15065. Epub 2018 Feb 17.

Abstract

The Barley stripe mosaic virus (BSMV) γb 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 γb. Here, we demonstrate that γb 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 γb phosphorylation spread similarly to the wild-type virus. Furthermore, the S96A mutant had reduced local and systemic γb 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 γb phosphorylation is functionally distinct from its RNA silencing suppressor activities. These results provide new insights into the function of γb 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.

Keywords: Nicotiana benthamiana; Barley stripe mosaic virus (BSMV); PKA; RNA silencing; host cell death response; phosphorylation; suppression; γb protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Death
  • Cyclic AMP-Dependent Protein Kinases / metabolism*
  • Host-Pathogen Interactions*
  • Mutation / genetics
  • Nicotiana / cytology*
  • Nicotiana / virology*
  • Phenotype
  • Phosphorylation
  • Phosphoserine / metabolism
  • Plant Diseases / virology
  • Plant Leaves / virology
  • Plant Viruses / pathogenicity*
  • RNA Interference*
  • Viral Proteins / chemistry
  • Viral Proteins / metabolism*
  • Virus Replication

Substances

  • Viral Proteins
  • Phosphoserine
  • Cyclic AMP-Dependent Protein Kinases

Supplementary concepts

  • Barley stripe mosaic virus