Genimivirus AL2 And L2 Proteins Interact With And Inactivate SNF1 Kinase
Abstract (Summary)The AL2 gene of begomoviruses such as Tomato golden mosaic virus (TGMV) encodes a transcriptional activator protein (TrAP) that is required for efficient expression from the viral coat protein (CP) and BR1 gene promoters. In contrast, L2, the positional homologue of AL2 in the related Beet curly top virus (BCTV, a curtovirus), is not required for CP expression, raising questions about the functional relationship between the AL2 and L2 gene products. AL21-83 and L2 were found to interact with an Arabidopsis SNF1-related kinase (hereafter SNF1) in a yeast two-hybrid screen. SNF1 is a serine/threonine kinase that plays a key role in the regulation of cellular stress responses and carbon metabolism in general. Using partially purified recombinant proteins expressed in E. coli or in insect (Sf9) cells, we have shown that AL2 and L2 are not phosphorylated by SNF1 in vitro. Instead, the consequence of AL2:SNF1 and L2:SNF1 interaction is that kinase activity, including autophosphorylation, is abolished. Since transgenic Nicotiana benthamiana and N. tabacum var. Samsun plants expressing a truncated AL2 gene (AL21-100, lacking the activation domain) or full-length L2 display a novel enhanced susceptibility (ES) phenotype following inoculation with RNA or DNA viruses, we hypothesize that ES conditioned by AL2 and L2 transgenes is due to inhibition of metabolic responses mediated by SNF1. This hypothesis is supported by the observations that transgenic N. benthamiana plants expressing an antisense SNF1 gene show ES, whereas plants that constitutively express a sense SNF1 transgene show enhanced resistance to virus infection. Arabidopsis SNF1 can complement yeast snf1 mutant allowing the cells to grow on media containing carbon sources other than glucose. However, co-expression of L2 with SNF1 in the snf1 mutant yeast blocks complementation, confirming functional L2:SNF1 interaction in vivo. To our knowledge, these studies provide the first evidence that SNF1 is targeted by viral pathogens, and implicate metabolic responses as a part of the plant’s defensive arsenal.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2003