Selective Interaction Between Chloroplast β-ATPase and TGB1L88 Retards Severe Symptoms Caused by Alternanthera mosaic virus Infection

The multifunctional triple gene block protein 1 (TGB1) of the Potexvirus Alternanthera mosaic virus (AltMV) has been reported to have silencing suppressor, cell-to-cell movement, and helicase functions. Yeast two hybrid screening using an Arabidopsis thaliana cDNA library with TGB1 as bait, and co-purification with TGB1 inclusion bodies identified several host proteins which interact with AltMV TGB1. Host protein interactions with TGB1 were confirmed by biomolecular fluorescence complementation, which showed positive TGB1 interaction with mitochondrial ATP synthase delta' chain subunit (ATP synthase delta'), light harvesting chlorophyll-protein complex I subunit A4 (LHCA4), chlorophyll a/b binding protein 1 (LHB1B2), chloroplast-localized IscA-like protein (ATCPISCA), and chloroplast ${\beta}$-ATPase. However, chloroplast ${\beta}$-ATPase interacts only with $TGB1_{L88}$, and not with weak silencing suppressor $TGB1_{L88}$. This selective interaction indicates that chloroplast ${\beta}$-ATPase is not required for AltMV movement and replication; however, TRV silencing of chloroplast ${\beta}$-ATPase in Nicotiana benthamiana induced severe tissue necrosis when plants were infected by AltMV $TGB1_{L88}$ but not AltMV $TGB1_{L88}$, suggesting that ${\beta}$-ATPase selectively responded to $TGB1_{L88}$ to induce defense responses.