TRANSGENIC SWEETPOTATO WITH AMYLOSE-FREE STARCH

Abstract

In the storage roots of sweetpotato (Ipomoea batatas (L.) Lam. cv. 'Kokei 14'), the starch consists of 18 to 20% of amylose and the other major component is amylopectin. Granule-bound starch synthase I (GBSSI) is one of the key enzymes to catalyze the formation of amylose. Amylose-free transgenic sweetpotato plants were successfully obtained by inhibition of the sweetpotato GBSSI gene expression through RNA interference. The gene construct consisting of an inverted repeat of the first exon separated by the first intron of GBSSI and driven by the CaMV 35S promoter was integrated into the sweetpotato genome by Agrobacterium tumefaciens-mediated transformation. About 73% of transgenic plants were inactivated by the expression of GBSSI, resulting in the storage roots containing only amylopectin but no amylose. The results clearly demonstrate that the amylose synthesis is completely inhibited in roots of sweetpotato plants which constitutively synthesized double stranded RNA of GBSSI. The RNA interference is very effective in inhibiting the gene expression in the starch metabolic pathway in sweetpotato.