Biochemical analysis of a novel allele of the OsPPDKB gene associated with floury endosperm

Abstract

Here we isolated and characterized floTR1, a new floury endosperm rice mutant. Whole genome sequence and analysis of a cleaved amplified polymorphic sequence marker found that the FloTR1 gene encodes a pyruvate orthophosphate dikinase B (OsPPDKB). The floTR1 mutant has a single G to A base substitution in the OsPPDKB gene, which results in a missense glycine to aspartate mutation. Although there was little change in the mRNA expression levels of OsPPDKB between floTR1 and the original variety (WT) plants, PPDK activity in the floTR1 developing endosperm was null. Recombinant enzyme analysis also found that aspartate replacement, as found in floTR1, resulted in the complete loss of PPDK activity in vitro. Analysis of other recombinant enzymes suggested that the spatial configuration such as size and direction of the side chain in the replaced amino acids predominantly affected its activity. The rice flour of floTR1 showed not only smaller particle size distribution and lower damaged starch content but also higher specific rice bread loaf volume than WT. Our data provides new insights into effects on OsPPDK activity caused by a SNP mutation and suggests applications for this new floury rice mutant.