Characterization of the replication-associated protein (Rep) promoter of an alpha-satellite associated with Tobacco curly shoot virus

Abstract

Alpha-satellites, nanovirus-like DNA components associated with begomoviruses (Family: Geminiviridae), encode a replication-associated protein (Rep) and depend on their helper viruses for spread within and between plants. In this study, using the Agrobacterium-mediated transient expression and stable transgenic systems, respectively we demonstrated that a 420 nt fragment located upstream of the Rep gene of Tobacco curly shoot alpha-satellite (TbCSA) was capable of initiating transcription of the β-glucuronidase (GUS) gene in tobacco plants, and the promoter activity was about 18% that of the Cauliflower mosaic virus (CaMV) 35S promoter. Using GUS and the green fluorescent protein (GFP) as the reporter gene, respectively deletion analysis indicated that 3’-terminus deletion of the 420 nt fragment was not functional, while the 5’-terminus deletions exhibited varying promoter activities. Furthermore, the 227 nt fragment located upstream of the Rep gene showed the same promoter activity as the longest 420 nt fragment and this should be considered as the minimal promoter sequence. To our knowledge, this is the first report on the promoter of an alpha-satellite associated with begomoviruses.

Key words: Promoter, alpha-satellite, Tobacco curly shoot virus, begomoviruses.