Identifying Sequences that Silence Coat Protein Expression in Spinach Curly Top Virus

Spinach curly top virus (SCTV) is a single stranded DNA virus of the family Geminiviridae. The infectious genome of this virus comprises a single DNA chromosome. SCTV causes severe disease in spinach plants resulting in stunted growth, chlorosis, occasionally necrosis. As a result spinach plants are unusable as market produce. In geminiviruses with two DNA chromosomes including Tomato golden mosaic virus (TGMV) and Cabbage leaf curl virus (CaLCuV) the coat protein (CP) gene is regulated by a second viral gene, AL2. In mesophyll the CP gene is activated by AL2, but in phloem the promoter is de-repressed, suggesting two mechanisms for regulation of CP expression. In SCTV we have recently demonstrated that the CP promoter is active in transient leaf infusion assays, unlike the TGMV and CaLCuV CP promoter. Thus, it appears that SCTV only utilizes repression as a regulatory mechanism for regulating CP. My project involves identification of viral sequences responsible for repression of the SCTV CP promoter. I begun cloning viral sequences into expression vectors containing the SCTV CP promoter fused to GUS reporter gene. Constructs will be introduced into Nicotiana benthamiana to generate transgenic plants. I will determine the effect of the viral sequences on SCTV CP expression using histochemical staining for GUS activity. Once these sequences have been identified we will determine how they cause repression of the CP promoter. Understanding how this virus causes disease through regulation of the CP gene will aid us in developing resistances to these viruses. Partially supported by UTSA WSRTP.