Abstract

DNA b 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 b contains a single gene, bC1, which encodes a pathogenicity protein responsible for symptom production. Transient expression studies in Nicotiana tabacum using the b-glucuronidase reporter gene driven by a bC1 promoter-deletion series of the DNA b associated with cotton leaf curl Multan virus identified a 68 nt region (between ”139 and ”207) which is important for bC1 transcription. This 68 nt region contains a G-box (CACGTG) located 143 nt upstream of the bC1 start codon. Mutation of the G-box resulted in a significant reduction in bC1 promoter activity and DNA b 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 b.