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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

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

Jiang Zhihao Z Zhang Kun K Li Zhaolei Z Li Zhenggang Z Yang Meng M Jin Xuejiao X Cao Qing Q Wang Xueting X Yue Ning N Li Dawei D Zhang Yongliang Y

PLoS pathogens 20200730 7

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 for ...[more]

PMID: 32730331

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Project description:Barley stripe mosaic virus (BSMV) spreads from cell to cell through the coordinated actions of three triple gene block (TGB) proteins (TGB1, TGB2, and TGB3) arranged in overlapping open reading frames (ORFs). Our previous studies (D. M. Lawrence and A. O. Jackson, J. Virol. 75:8712-8723, 2001; D. M. Lawrence and A. O. Jackson, Mol. Plant Pathol. 2:65-75, 2001) have shown that each of these proteins is required for cell-to-cell movement in monocot and dicot hosts. We recently found (H.-S. Lim, J. N. Bragg, U. Ganesan, D. M. Lawrence, J. Yu, M. Isogai, J. Hammond, and A. O. Jackson, J. Virol. 82:4991-5006, 2008) that TGB1 engages in homologous interactions leading to the formation of a ribonucleoprotein complex containing viral genomic and messenger RNAs, and we have also demonstrated that TGB3 functions in heterologous interactions with TGB1 and TGB2. We have now used Agrobacterium tumefaciens-mediated protein expression in Nicotiana benthamiana leaf cells and site-specific mutagenesis to determine how TGB protein interactions influence their subcellular localization and virus spread. Confocal microscopy revealed that the TGB3 protein localizes at the cell wall (CW) in close association with plasmodesmata and that the deletion or mutagenesis of a single amino acid at the immediate C terminus can affect CW targeting. TGB3 also directed the localization of TGB2 from the endoplasmic reticulum to the CW, and this targeting was shown to be dependent on interactions between the TGB2 and TGB3 proteins. The optimal localization of the TGB1 protein at the CW also required TGB2 and TGB3 interactions, but in this context, site-specific TGB1 helicase motif mutants varied in their localization patterns. The results suggest that the ability of TGB1 to engage in homologous binding interactions is not essential for targeting to the CW. However, the relative expression levels of TGB2 and TGB3 influenced the cytosolic and CW distributions of TGB1 and TGB2. Moreover, in both cases, localization at the CW was optimal at the 10:1 TGB2-to-TGB3 ratios occurring in virus infections, and mutations reducing CW localization had corresponding effects on BSMV movement phenotypes. These data support a model whereby TGB protein interactions function in the subcellular targeting of movement protein complexes and the ability of BSMV to move from cell to cell.

Dataset Information

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

Publications

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

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