Identification of a Minimal Sequence Required for Activation of the Tomato Golden Mosaic Virus Coat Protein Promoter in Protoplasts

Transient expression studies using a Nicotiana benthamiana suspension cell-derived protoplast system have identified a minimal sequence that is necessary and sufficient for activation of the tomato golden mosaic virus coat protein (CP) promoter by the viral TrAP protein (also called AL2). The sequence has a bipartite arrangement in which elements located between −125 to −107 and −96 to −60 from the transcription start site are both required for TrAP-mediated activation. One of the sequences (−96 to −60) also appears to interact with a repressor, as its deletion increases basal promoter activity in the absence of TrAP. That competition experiments using the −107 to −60 sequence to titrate the repressor also resulted in increased basal transcription is consistent with this idea. Thus, in a protoplast system which models mesophyll, regulation of the minimal CP promoter involves both activation and derepression by TrAP.