Investigation of the endosperm-specific sucrose synthase promoter from rice using transient expression of reporter genes in guar seed tissue

We report the investigation of an endosperm-specific promoter from the rsus3 gene from rice (Oryza sativa). The promoter was characterized by deletion analysis and transient expression in guar (Cyamopsis tetragonoloba) seed-tissue. Transient expression was monitored by histochemical GUS assay, and quantitative dual reporter assays comprising firefly luciferase as a test reporter, and Renilla luciferase and GUS as reference reporters. These revealed high expression levels of the reporter genes directed by the rsus3 promoter in guar endosperm. Specificity for this tissue in seeds was apparent from a virtual absence of reporter activity in guar cotyledons. Removal of a putative intron region only slightly raised the expression level, whereas duplication of the minimal promoter region, in a tandem-repeat rsus3 promoter construct, retained endosperm specificity in guar, and displayed three times the reporter activity observed with the single copy construct.