Abstract
The C1 promoter expressing the AC1 gene, and V1 promoter expressing the AV1 gene are located in opposite orientations in the large intergenic region of the Cotton leaf curl Burewala virus (CLCuBuV) genome. Agro-infiltration was used to transiently express putative promoter constructs in Nicotiana tabacum and Gossypium hirsutum leaves, which was monitored by a GUS reporter gene, and revealed that the bidirectional promoter of CLCuBuV transcriptionally regulates both the AC1 and AV1 genes. The CLCuBuV C1 gene promoter showed a strong, consistent transient expression of the reporter gene (GUS) in N. tabacum and G. hirsutum leaves and exhibited GUS activity two- to three-fold higher than the CaMV 35S promoter. The CLCuBuV bidirectional genepromoter is a nearly constitutive promoter that contains basic conserved elements. Many cis-regulatory elements (CREs) were also analyzed within the bidirectional plant promoters of CLCuBuV and closely related geminiviruses, which may be helpful in understanding the transcriptional regulation of both the virus and host plant.
Highlights
Geminiviruses are plant pathogens with small, circular single stranded DNA genomes of 2.5–3.0 kb that are encapsidated in characteristic twin quasi-icosahedral particles
We found that the Cotton leaf curl Burewala virus (CLCuBuV) C1 promoter had strong and consistent transient expression in plant leaves compared to the CLCuBuV V1 and Cauliflower mosaic virus (CaMV) 35S promoters
The CLCuBuV bidirectional gene promoters were isolated from the large intergenic region (LIR) of the DNA-A genomic clone from CLCuBuV, as previously characterized [25]
Summary
Geminiviruses are plant pathogens with small, circular single stranded (ss) DNA genomes of 2.5–3.0 kb that are encapsidated in characteristic twin quasi-icosahedral particles. The large intergenic region (LIR) of the DNA-A component from the monopartite begomovirus genome contains plant cis-acting DNA regulatory elements and transcription factor binding sites (TFBs) required for the control of viral gene expression and replication [6]. Multan (CLCuMuV) [4], Wheat dwarf geminivirus (WDG) [17], Mungbean yellow mosaic India virus (MYMIV) [18], and Mungbean yellow mosaic geminivirus (MYMV) [19] revealed that this region, which is located between the 5' ends of the first complementary and virion sense open reading frames (ORFs), possesses promoter activity and is essential for the bidirectional transcription of both complementary (Rep) and virion (Cp) genes. Recombinant DNA technology to combat the spatio-temporal expression pattern of an insecticidal gene (Cry1Ac) in transgenic cotton in the future
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