Identification of sequence elements regulating promoter activity and replication of a monopartite begomovirus-associated DNA β satellite

Abstract

DNA β is a circular single-stranded satellite DNA associated with certain monopartite begomoviruses (family Geminiviridae) which causes economically important diseases such as cotton leaf curl disease. DNA β contains a single gene, βC1, which encodes a pathogenicity protein responsible for symptom production. Transient expression studies in Nicotiana tabacum using the β-glucuronidase reporter gene driven by a βC1 promoter-deletion series of the DNA β associated with cotton leaf curl Multan virus identified a 68 nt region (between –139 and –207) which is important for βC1 transcription. This 68 nt region contains a G-box (CACGTG) located 143 nt upstream of the βC1 start codon. Mutation of the G-box resulted in a significant reduction in βC1 promoter activity and DNA β replication efficiency. In addition, the G-box motif was found to bind specifically to a protein(s) in nuclear extracts prepared from tobacco leaf tissues. Our results indicate that interaction of the G-box motif with host nuclear factors is important for efficient gene expression and replication of DNA β.