Impact of a viral RNA silencing suppressor on SnRk1-mediated autophagy - Food security is a significant issue worldwide, with health problems related to diet becoming an increased burden on society. Food availability is strongly impacted by crop loss, and US crops are vulnerable to geminivirus diseases that are difficult to control. Current control measures include limiting geminivirus vector populations using pesticides, which are a significant health concern. Pesticides are ubiquitous in the environment and most act by disrupting nervous system function, and so research to discover alternative methods of controlling geminivirus infections is warranted. The ability of a host to resist infection depends on defense-counterdefense interactions between pathogen and host. Many plant viruses, including geminiviruses, encode RNA silencing suppressors, which can be viewed as effectors that suppress host innate immune responses. Key unanswered questions in the geminivirus field are how RNA silencing and autophagy coordinate the antiviral response, and how viral silencing suppressors (VSRs) subvert that response. Geminivirus VSRs (AC2/C2) inactivates SnRK1, an SNF1-related protein kinase, resulting in differential expression of autophagy-related genes. In addition, geminivirus VSRs interact with, and relocalize, an endogenous regulator of gene silencing (rgsCaM). This supports our hypothesis that geminivirus VSRs subvert the SnRK1/autophagy pathway to suppress RNA silencing. We plan to test the hypothesis with three Specific Aims. In Aim1, we will Investigate the role of VSRs in autophagy. We will determine i) the impact of AC2 on autophagy, ii) Impact of AC2 on SnRK1 induction of autophagy, and iii) impact of SnRK1 inhibition on AC2 accumulation. Aim 2 will characterize the effect of SnRK1 on rgsCaM function. We will investigate i) the role of rgsCaM on AC2 accumulation, ii) role of on AC2 and SGS3 accumulation, and iii) role of SnRK1 on RDR6 expression. For Aim 3 we will investigate i) the effect of autophagy on RNA silencing, and ii) the effect of autophagy on host recovery from infection. This work will increase our understanding of the roles of rgsCaM and autophagy in regulation of RNA silencing, part of the plant innate defense response, and provide us with the molecular basis of how geminiviruses target autophagy during infection. As pathways targeted by geminivirus VSRs are highly conserved, links between RNA silencing, autophagy and SnRK1 regulation of stress responses can have important implications for host defense and control of dsRNA-inducing pathways in both plants and mammals. It should be noted that absence of the interferon pathway in plants, which like RNA silencing can be triggered by dsRNA, will simplify data interpretation. Moreover, this work will pave the way for development of strategies based on disrupting interactions between virus VSRs and host innate immune pathways. This could lead to broad- based resistance to this rapidly expanding group of plant viral pathogens, increasing food security and improving public health by reducing harmful pesticide use.
