The Barley stripe mosaic virus ?b protein promotes viral cell-to-cell movement by enhancing ATPase-mediated assembly of ribonucleoprotein movement complexes.

ABSTRACT: Nine genera of viruses in five different families use triple gene block (TGB) proteins for virus movement. The TGB modules fall into two classes: hordei-like and potex-like. Although TGB-mediated viral movement has been extensively studied, determination of the constituents of the viral ribonucleoprotein (vRNP) movement complexes and the mechanisms underlying their involvement in vRNP-mediated movement are far from complete. In the current study, immunoprecipitation of TGB1 protein complexes formed during Barley stripe mosaic virus (BSMV) infection revealed the presence of the ?b protein in the products. Further experiments demonstrated that TGB1 interacts with ?b in vitro and in vivo, and that ?b-TGB1 localizes at the periphery of chloroplasts and plasmodesmata (PD). Subcellular localization analyses of the ?b protein in Nicotiana benthamiana epidermal cells indicated that in addition to chloroplast localization, ?b also targets the ER, actin filaments and PD at different stages of viral infection. By tracking ?b localization during BSMV infection, we demonstrated that ?b is required for efficient cell-to-cell movement. The N-terminus of ?b interacts with the TGB1 ATPase/helicase domain and enhances ATPase activity of the domain. Inactivation of the TGB1 ATPase activity also significantly impaired PD targeting. In vitro translation together with co-immunoprecipitation (co-IP) analyses revealed that TGB1-TGB3-TGB2 complex formation is enhanced by ATP hydrolysis. The ?b protein positively regulates complex formation in the presence of ATP, suggesting that ?b has a novel role in BSMV cell-to-cell movement by directly promoting TGB1 ATPase-mediated vRNP movement complex assembly. We further demonstrated that elimination of ATPase activity abrogates PD and actin targeting of Potato virus X (PVX) and Beet necrotic yellow vein virus (BNYVV) TGB1 proteins. These results expand our understanding of the multifunctional roles of ?b and provide new insight into the functions of TGB1 ATPase domains in the movement of TGB-encoding viruses.

SUBMITTER: Jiang Z 

PROVIDER: S-EPMC7419011 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature