Analyzing plant stress granules in response to plant viruses

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Plant viruses have the ability to redirect host machineries and processes to establish a productive infection. Virus-host interactions lead to the reprogramming of the plant cell cycle and transcriptional controls, inhibition of cell death pathways, interference with cell signaling and protein turnover, and suppression defense pathways. We have focused on the geminiviruses Abutilon mosaic virus (AbMV), Cleome leaf crumple virus (ClLCrV) and potyvirus Turnip mosic virus (TuMV) as model systems to investigate plant virus host interactions in detail. TuMV is an ssRNA virus which genome encodes for a large polyprotein and an additional small protein. The polyprotein is cleaved into several proteins and the N-terminal protein is called P1. P1 generally functions as a protease, but we suspect an additional function, the interference with stress granules (SGs). AbMV and ClLCrV belong to the genus Begomovirus and their genome consists of two circular ssDNA molecules: DNA A and DNA B. DNA A encodes for all proteins important for replication and encapsidation, whereas DNA B encodes proteins essential for viral transport. The two DNA B-encoded proteins, the nuclear-shuttle protein (NSP) and movement protein (MP), mediate the viral transport processes. Several studies provide evidence that NSP facilitates trafficking of viral DNA (vDNA) into and out of the nucleus. We recently could show that NSP interacts with the Ras-GAP SH3 domain binding protein (G3BP), which is an integral part of SGs. SGs are cytoplasmic localized RNA-protein complexes that form when abiotic/biotic stresses are applied. In SGs preassembled translation complexes are stalled to down-regulate gene expression to promote immune response, but gene expression can also be resumed when stress conditions diminish. G3BP is a key factor for SGs formation in the mammalian system and often targeted by viruses. The NSP interacts with G3BP, which suggests control and regulation of plant SGs in stress response to optimize cellular conditions for the production of viral proteins. Characterization of plant SGs and their role in virus infection is poorly investigated. Thus, the overall aim of this study is to analyze and characterize plant SGs and to elucidate their role in plant stress response, with special emphasis on viral infections. The G3BP is the key enzyme in SG function, and therefore, we will characterize the Arabidopsis G3BP(s) by analyzing G3BP OEX and KO Arabidopsis plants under ambient and stress conditions. We will follow a proteomics approach to analyze the composition of SGs. We will investigate the functional role of virus proteins, e. g. NSP and P1, to understand the interplay of virus and SGs in the plant virus infection cycle. Taken together this will enable us to understand not only the cellular complexes but also the strategies and mechanisms a plant virus needs to employ and to re-program a plant cell to its favor.