Fine Mapping and Candidate Gene Analysis of the Hwacheong Sugary-2 Mutant in Rice

Abstract

Two sugary mutants, Hwacheong sugary-1 (Hsu1) and Hwacheong sugary-2 (Hsu2) were obtained by chemical mutagenesis from japonica cultivar, Hwacheongbyo. Both mutants exhibited wrinkled, translucent, and amber-colored endosperm with high soluble sugar content. The grain of Hsu2 mutant was less wrinkled than that of Hsu1 thus Hsu2 can be polished easily and commercially feasible. To identify the sequence of sugary genes, map-based cloning strategy was applied. Genetic study revealed that the phenotype of Hsu1 was controlled by isoamylase gene which was located on chromosome 8, known as sugary-1 (su-1). However, the phenotype of Hsu2 differed slightly from the phenotype of Hsu1. Thus, we hypothesize that the other gene controlling the Hsu2 mutant phenotype may have a role in weakening the effect of the su-1. Through genetic analysis, the phenotype of Hsu2 was controlled by epistatic interaction of two recessive genes, one of which was the same gene as su-1. The other candidate gene of the Hsu2 (su-2), named 1,4-α-glucan-branching enzyme, was found to be located on chromosome 4. These results will be helpful in elucidating the starch synthesis pathway related to rice endosperm variation and in breeding sugary endosperm rice varieties.