Identification of cis elements involved in Commelina yellow mottle virus promoter activity.

Commelina yellow mottle virus (CoYMV) is a double-stranded DNA virus that infects a monocot host. A promoter fragment isolated from CoYMV is a strong promoter when assayed after transient introduction into monocot and dicot suspension cells and is highly active in vascular cells of flowers, leaves, stems and roots of stably transformed tobacco plants. Here it is reported that in stably transformed maize calli and transgenic tobacco leaves the CoYMV and CaMV 35S promoters exhibit similar amounts of activity. Deletion of the sequences located distal to nucleotide -230 relative to the start of transcription has no significant effect on promoter strength or tissue specificity. The region between -230 and -200 shares sequence similarity with the as-1 promoter element of the CaMV 35S promoter. Deletion of this as-1-like motif decreases promoter activity in maize suspension cells by 85%. Analysis of deletions affecting the -200 to -52 region indicates that sequences located between -159 and -84 are required for activity in vascular tissues. In addition, this region exhibits properties of a vascular tissue-specific enhancer since it confers vascular expression in an orientation-independent manner when fused to promoters that are not normally active in vascular tissues.