Isolation and identification of a super strong plant promoter from cotton leaf curl Multan virus

The activity of the C1 and the V1 gene promoter of cotton leaf curl Multan virus (CLCuMV) was investigated in transgenic plants with the gus gene as a reporter gene. Quantitative GUS activity analysis of the transgenic plant leaves showed the average activity of the CLCuMV C1 gene promoter was 3- to 5-fold higher than that of the CaMV 35S promoter, with maximal expression being 10-fold higher. CLCuMV V1 gene promoter activity was only about 1/10th that of the CaMV 35S promoter in the absence of trans-activator C2. Histochemical GUS staining of the transgenic plants indicated that the CLCuMV C1 gene promoter was active in leaves, stems, roots and almost all reproductive organs. Functional analysis of promoter 5'-deletion series indicated that promoter activity of a 257 nucleotide fragment (-257 to the transcription initiation site) and a 241 nucleotide fragment (-241 to the transcription initiation site) were 5-fold and 2-fold stronger than that of the full-length CLCuMV C1 promoter respectively. These results demonstrate that the CLCuMV C1 promoter is a super-strong near-constitutive promoter in plants and has great application potential for plant genetic engineering studies.