Abstract
Starch biosynthesis in plants is the complex system where the multiple isozymes of starch synthase, branching enzyme (BE) and debranching enzyme are involved. As an approach to dissect the interplay between these enzymes, we are developing the expression system for rice genes in the cyanobacterium, Synechococcus sp. PCC 7942, that has much simpler set of enzymes for polyglucan metabolism. Defects of BEIIb and isoamylase-1 (ISA-1) in rice endosperm led to the marked alterations in the branching pattern and property of polysaccharide. In this study, these genes were introduced in the BE and ISA mutants of Synechococcus, respectively.
In the BEIIb transformant, glucan chains with DP 7 - 8 were decreased and short chains (DP = 5) were inversely increased. In the ISA-1 transformant the amount of very short chains (DP 2 - 3) was decreased as compared to its parent strain (ISA mutant).
