Molecular Genetic Basis of Starch Biosynthesis and Waxy Allelic Variation in Rice Grain Quality

The culinary, nutritional, and industrial properties of rice (Oryza sativa L.) grains are fundamentally governed by the structural arrangement of endosperm starch, a complex physiological phenotype shaped by genetic architecture and environmental conditions. This review provides a comprehensive synthesis of the molecular pathways driving starch biosynthesis in rice, centering on allelic diversity within the Waxy (Wx) locus, which codes for Granule-Bound Starch Synthase I (GBSSI). Sequence variations in Wx critically modulate amylose synthesis by altering transcription levels and post-transcriptional events, primarily pre-mRNA splicing accuracy. The resulting amylose-to-amylopectin ratio directly dictates grain firmness, retrogradation rates, digestibility, and postprandial metabolic responses. Although key biosynthetic enzymes have been characterized, the overarching regulatory network and its vulnerability to ambient temperature stress during grain maturation demand further elucidation. Harnessing modern molecular markers and genomic selection targeting these genetic networks offers promising avenues for precision breeding of rice cultivars tailored for specific end-use functionalities.