Jin-gyung Hur and Keith R. Davis

Department of Plant Biology, The Ohio State University, Columbus, OH 43210

BCTV is a single strand DNA virus which causes distinct symptoms on Arabidopsis thaliana. These symptoms include severe stunting, curly top, anthocyanin accumulation and malformed floral structures. The degree and timing of A. thaliana is dependent on the BCTV viral strain used. Infection of A. thaliana with BCTV-CFH results in more severe symptoms with a shorter latent period, compared with infection by BCTV-Logan. Expression of the CFH and Logan seven open reading frames (ORFs), three rightward virion sense strand ORFs and four leftward complementary sense ORFs, is driven by a bi-directional promoter. To investigate the activity of the BCTV viral bi-directional promoter in plants upon infectionby virus, viral promoter/GUS constructs were made and used to make transgenic A. thaliana. Transgenic plants with each construct (CFH or Logan) showed distinct reporter gene expression level. Generally, the viral promoters were active in seedlings in actively dividing tissues such as root tips and apical meristems. As plants matured, promoter activity diminished. Infection of mature plants by virus restored promoter activity. To our surprise, the promoter from the "weaker" Logan virus showed stronger activity than the CFH promoter. We also found an interesting motif of 30bp which is tandemly repeated three times in the Logan promoter; only one copy is found in the CFH promoter. Further study of this motif suggested that this repeating motif is responsible for the stronger viral promoter activity of Logan promoter.