Promoter regulatory domain identification of cassava starch synthase IIb gene in transgenic tobacco

Soluble starch synthase is a key enzyme in the starch biosynthesis pathway, and its enzyme activity significantly influences starch components in cassava storage root. However, studies on the regulation mechanism of soluble starch synthase gene are rare. In this study, we cloned the 5′ flanking sequence of the MeSSIIb gene and predicted the distribution of cis-elements. The region from −453 to −1 was considered the primary core promoter by the quantitative detection of GUS activity in transgenic tobacco plants containing 5′ truncated promoters fused with the GUS gene. Analysis results clarified that the region from −531 to −454 significantly repressed promoter activity. The region from −453 to −388 was a repressive domain of ethylene, and some unknown drought responsive cis-elements were located in the region from −387 to −1. These findings will provide useful information on the functional assay and transcriptional regulation mechanisms of the MeSSIIb gene.