Insights into the control of geminiviral promoters

Geminiviruses constitute one of the largest groups of plant viruses, having characteristic twinned geminate particles encapsidating small circular single-stranded DNA molecules. Geminiviral promoters are generally located within the intergenic region, although promoters have also been detected within the genes. Similarly, the geminivirus-associated betasatellite also harbours a promoter element for driving the expression of its only ORF. These regulatory elements of geminiviral and satellite origins have been subject of great interest to develop heterologous gene expression modules. Geminiviral promoter and regulatory elements show a complex regulation that is mediated by several host as well as viral proteins. Here, the structural and functional features of geminiviral and satellite promoters are discussed along with their regulation by plant and viral proteins. Although generalization in many cases is difficult and demands further studies, a pattern is seen to emerge on the regulation of the promoters.