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Abstract
Chloroplast-bound vesicles are key components in viral replication complexes (VRCs) of potyviruses. The potyviral VRCs are induced by the second 6 kDa protein (6K2) and contain at least viral RNA and nuclear inclusion protein b. To date, no chloroplast protein has been identified to interact with 6K2 and involve in potyvirus replication. In this paper, we showed that the Photosystem II oxygen evolution complex protein of Nicotiana benthamiana (NbPsbO1) was a chloroplast protein interacting with 6K2 of Tobacco vein banding mosaic virus (TVBMV; genus Potyvirus) and present in the VRCs. The first 6 kDa protein (6K1) was recruited to VRCs by 6K2 but had no interaction with NbPSbO1. Knockdown of NbPsbO1 gene expression in N. benthamiana plants through virus-induced gene silencing significantly decreased the accumulation levels of TVBMV and another potyvirus Potato virus Y, but not Potato virus X of genus Potexvirus. Amino acid substitutions in 6K2 that disrupted its interaction with NbPsbO1 also affected the replication of TVBMV. NbPsbP1 and NbPsbQ1, two other components of the Photosystem II oxygen evolution complex had no interaction with 6K2 and no effect on TVBMV replication. To conclude, 6K2 recruits 6K1 to VRCs and hijacks chloroplast protein NbPsbO1 to regulate potyvirus replication.
Highlights
Chloroplast is the metabolic energy manufacture in plant
We showed that Tobacco vein banding mosaic virus (TVBMV) 6K1 and NbPsbO1, a component of the PSII Oxygen-Evolving Complex, were essential factors in the TVBMV replication complex
We demonstrated that viral 6K1 and NbPsbO1 interacted with 6K2 and 6K1 was recruited to viral replication complexes (VRCs) by 6K2
Summary
Chloroplast is the metabolic energy manufacture in plant. It is known to have an important role in plant virus replication. Turnip yellow mosaic virus 140 K protein contains methyltransferase, proteinase and NTPase/helicase motifs and targets chloroplast envelope. This 140 K protein can recruit the 66 K viral RNA-dependent RNA polymerase (RdRp) to chloroplast periphery[8,9]. Replication of many potyviruses was shown to associate with chloroplast[21,22,23,24,25], no chloroplast protein has been reported to interact with potyvirus 6K2 protein, which induces the formation of VRCs. Potyviruses (genus Potyvirus, family Potyviridae) are members in the picornarvirus-like superfamily[26,27]. Our results indicate that the 6K1 is an essential component in potyviral VRCs and NbPsbO1 is an important host factor involved in potyvirus replication in plant via interacting with 6K2
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