Abstract
To reveal the function of SSIVb in starch biosynthesis of developing rice endosperm, we generated the ΔSSIIIa/ ΔSSIVb double mutant lines. The SSIVb single mutation did not affect seed morphology, grain weight, starch granule morphology, and amylopectin chain length distribution. In contrast, kernels of the double mutant lines had an opaque appearance. Their dehulled grain weight and starch content were lower (81%-86% and 71%, respectively) than those of the wild type. The endosperm starch granules of the double mutants formed entirely spherical shape and were loosely packed in the endosperm cells. The amylopectin B2 to B4 chains with degree of polymerization (DP) larger than 37 in the double mutant were much more reduced than these of the Δ SSIIIa . Amylose content was higher than WT and the Δ SSIIIa line. These results suggest that the function of SSIVb is overlapped with that of SSIIIa. We will also discuss the pleiotropic effects on the other enzymes involved in starch biosynthesis.
