A sugary mutant with low total starch and high sugar contents was compared with its wild type Sindongjin for
grain-filling caryopses. In the present study, developing seeds of Sindongjin and sugary mutant from the 11th
day after flowering (DAF) were subjected to RNA sequencing (RNA-Seq). A total of 30,385 and 32,243 genes
were identified in Sindongjin and sugary mutant. Transcriptomic change analysis showed that 7713 differentially
expressed genes (DEGs) (log2 fold change ≥1, false discovery rate (FDR) ≤ 0.001) were identified based on our
RNA-Seq data, with 7239 genes up-regulated and 474 down-regulated in the sugary mutant. A large number of
DEGs were found related to metabolic, biosynthesis of secondary metabolites, plant-pathogen interaction,
plant hormone signal transduction and starch/sugar metabolism. Detailed pathway dissection and quantitative
real time PCR (qRT-PCR) demonstrated that most genes involved in sucrose to starch synthesis are upregulated, whereas the expression of the ADP-glucose pyrophosphorylase small subunit (OsAGPS2b) catalyzing
the first committed step of starch biosynthesis was specifically inhibited during the grain-filling stage in sugary
mutant. Further analysis suggested that the OsAGPS2b is a considerable candidate gene responsible for phenotype
of sugary mutant.