The Arabidopsis TCP24 Transcription Factor Interacts With the Geminivirus Trap Protein to Regulate Begomovirus Coat Protein Expression

The viral protein TrAP has been shown to mediate tissue-specific expression of the CP genes of several begomoviruses, including Tomato golden mosaic virus (TGMV) and Cabbage leaf curl virus (CaLCuV). Given that TrAP does not itself effectively bind dsDNA, this would suggest that it is recruited to responsive promoters through interactions with host-derived cellular proteins. This hypothesis is supported by the observation that TrAP can form a complex with the host protein TIFY4B on the CP promoter. In this study, we identified a second plant-specific DNA-binding protein, Arabidopsis TCP24 (AtTCP24) that can directly bind a conserved late element (CLE) found within the CP promoter. AtTCP24 is able to interact with AtTIFY4B, AtTIE1 and TrAP proteins within the nuclear compartment of a plant cell. These results combined with a previous observation that AtTCP24 acts to negatively regulate transcription of target genes we propose that AtTCP24 represses CP promoter activity during the early phase of the infection cycle. Support for repression of the CP gene by AtTCP24 was shown using reporter gene assays which demonstrated that CP activity was lower in plants over-expressing AtTCP24. Furthermore, qPCR results revealed that CP mRNA levels were reduced in plants over-expressing AtTCP24. Therefore, we conclude that multiple cellular proteins are able to directly interact with the viral protein TrAP, and that AtTCP24 is able to negatively regulate the begomovirus CP promoter in vivo, possibly through interactions with AtTIFY4B and/or AtTIE1.