CLONING AND EXPRESSION OF RICE (ORYZA-SATIVA) SUCROSE SYNTHASE-1 (RSS1) IN DEVELOPING SEED ENDOSPERM

A previously cloned cDNA to rice (Oryza sativa L.) sucrose synthase 1 (RSs1) was used to determine spatial expression of the gene in rice ti ssues and temporal expression in developing rice endosperm. RSs1 was e xpressed predominantly in the endosperm of milky stage rice seeds with maximum expression at 3-5 days after pollination which were 8-10-fold over leaf levels. The peak in RSs1 transcript levels preceded the pea k of enzyme activity which occured 9-11 days after pollination. RSs1 t ranscript and activity levels were analyzed in two starch deficient mu tants of rice to determine if the lesion in these mutants resides at t he locus for RSs1. No correlation between sucrose synthase activity an d starch biosynthesis was seen in these mutants, although slight eleva tions of RSs1 transcript levels were observed.