Isolation, characterization and expression analysis of starch synthase I from wheat (Triticum aestivum L.)

Two full-length cDNA, wSsI-I and wSsI-II, encoding wheat starch synthase I (wSSI; E.C. 2.4.1.21) were isolated from a wheat endosperm cDNA library. Both cDNA clones were able to complement a glycogen synthase mutation present in the E. coli strain, RH98, thus demonstrating that the cDNA clones encoded functional starch synthases. RNA gel-blot analysis revealed that wSsI transcripts were produced in leaf, stem, root, pre-anthesis floret, ovary, pollen and endosperm. In the endosperm, the amount of wSsI transcripts accumulated was higher at 5–10 days-post-anthesis (DPA) than at 15–25 DPA. During the endosperm development, the relative abundance of wSSI did not vary in starch granules, whereas, wSSI concentration in the endosperm soluble fractions was highest from ten to 15 DPA, and below detection levels at five DPA. On a per kernel basis, wSSI exhibited similar concentration from 15 to 25 DPA in endosperm soluble fractions, but at considerably higher concentrations in starch granules as compared to endosperm soluble fractions.