The analysis for alteration in starch biosynthesis metabolism in a japonica rice grain mutant which does not accumulate starch

Abstract

Rice grain‒filling is an important agronomic trait that contributes greatly to grain weight. A grain mutant from the japonica cultivar Nipponbare by mutagenesis with ethyl methane sulfonate (EMS), which had no accumulation of starch granules in endosperm with a transparent liquid during grain filling stage, was used to analyze the caryopsis development and starch biosynthesis metabolism in present study. Measurement of soluble substances in the liquid of developing endosperm showed that there was remarkably higher soluble sugar content in this no starch mutant. Semi‒quantitative reverse transcription‒PCR (RT‒PCR) analysis of the starch‒synthesizing genes revealed that soluble starch synthase1 (SSS1) gene could be normally expressed in the mutant. Substantially lower expressions of starch branching enzyme1 (SBE1), isoamylase1 (ISA1) and pullulanase (PUL) were detected in the no starch mutant compared with the wild type, whereas the expression of ADP‒glucose pyrophosphorylase large subunit 1 (AGPL1) and ADP‒glucose pyrophosphorylase small subunit 1 (AGPS1) were visibly increased. The measurements of the key enzymatic activities involving in starch biosynthesis suggested that there was a significant reduction in the activities of starch debranching enzyme (DBE) and starch branching enzyme (SBE) in the transparent liquid endosperm of the no starch mutant, which coincided with their down‒regulation expression at transcriptional levels. These results suggest that the transparent liquid with no starch accumulation at the filling stage in the glume of the mutant was likely due to abnormal transcriptional and enzymatic activities related to the DBE and/or SBE genes loci mutant.