| ADP-glucose pyrophosphorylase (AGPase, EC2.7.7.27) is a key enzyme in starch synthesis. Tomato Agp S1 subunit gene and its promoter were isolated from a tomato genomic library. The Agp S1 structural gene contains 14 introns. A TATA box at the -57kp and a CCAAT box at -8bp position were identified. The tomato Agp S1 promoter is active in specific tissues of all organs. Its activity is localized in the guard cells and veins of the leaf, in the root cap and vascular tissues, in the starch sheath cells of the stem and in the ovary and stamens of the flower. It is also active in pollen, seeds and in the inner pericarp wall and placental tissue of the developing tomato fruit. No activity was observed in mesophyll cells, or in the ovaries at anthesis.;Only 0.4kb upstream fragment of Agp S1 promoters was required for activity in the leaves and flowers. There is a negative regulatory element between -0.4 and -0.8kb region and three positive regulatory elements in the -0.4kb region, -0.8 to -1.3kb region and -1.3 to -3.0kb region respectively for the regulation of expression in the stem, root cap and root vascular tissues. The Agp S1 promoter also has 4 cis-acting elements similar to other plant genes.;Tomato Agp S3 gene and its promoter were also isolated from a tomato genomic library. The Agp S3 structural gene contains at least 8 introns. There is a CCAAT box at the -115bp position and multiple GC rich regions around the CCAAT box, but no TATA box was found. The tomato Agp S3 promoter is also active in specific tissues, but most importantly in the leaf mesophyll cells. Only 0.5kb upstream fragment of Agp S3 promoter is required for expression in transgenic plants.;Agp S1, S2 and B are highly expressed in fruit from 10 to 25 days after anthesis. Agp S3 is only weakly expressed in fruit. Sucrose significantly activated the expression of Agp S1, S2 and B in both leaves and fruits. Agp S1 exhibits the highest degree of regulation by sucrose. Agp S3 was not affected by sucrose. |
