3 years ago

Disruption of the methionine cycle and reduced cellular gluthathione levels underlie potex-potyvirus synergism in Nicotiana benthamiana

Swarnalok De, Matti Wahlsten, Gabriela Chavez-Calvillo, Kristiina Mäkinen
Infection caused by synergistic interaction of two plant viruses is typically manifested by severe symptoms and increased accumulation of either virus. In potex-potyviral synergism potyviral RNA silencing suppressor HCPro is known to enhance the pathogenicity of the potexvirus counterpart. In line with this Potato virus X (PVX; genus Potexvirus) genomic RNA (gRNA) accumulation and gene expression from subgenomic RNA (sgRNA) increased in Nicotiana benthamiana by Potato virus A (PVA; genus Potyvirus) HCPro expression. We recently demonstrated that PVA HCPro interferes with the host cell methionine cycle by interacting with its key enzymes S-adenosyl-L-methionine synthetase (SAMS) and S-adenosyl-L-homocysteine hydrolase (SAHH). To study the involvement of methionine cycle enzymes in PVX infection we knocked SAMS and SAHH down. Increased PVX sgRNA expression between 3-9 days post infection (dpi) and upregulation of (-)-strand gRNA accumulation at 9 dpi was observed in SAHH-silenced background. We found that SAMS and SAHH silencing caused also a significant reduction in glutathione (GSH) concentration specifically in PVX infected plants between 2-9 dpi. Interestingly, HCpro expression in PVX infected plants caused an even stronger reduction in GSH levels than SAMS+SAHH silencing and a similar level of reduction was achieved also by knocking down GSH synthetase. PVX sgRNA expression was increased in GSH synthetase silenced background. GSH is a major antioxidant of plant cells and therefore GSH shortage may explain the strong oxidative stress and the severe symptoms observed during potex-potyvirus mixed infection. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/mpp.12661

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