Genes controlling grain chalkiness in rice

With rising living standards, there is an increasing demand for high-quality rice. Rice quality is mainly defined by milling quality, appearance quality, cooking and eating quality, and nutrition quality. Among them, chalkiness is a key trait for appearance quality, which adversely affects cooking and eating quality, head rice yield, and commercial value. Therefore, chalkiness is undesirable, and reducing chalkiness is a major goal in rice quality improvement. However, chalkiness is a complex trait jointly influenced by genetic and environmental factors, making its genetic study and precision improvement a huge challenge. With the rapid development of molecular techniques, much knowledge has been gained about the genes and molecular networks involved in chalkiness formation. The present review describes the major environmental factors affecting chalkiness and summarizes the quantitative trait loci (QTL) associated with chalkiness. More than 150 genes related to chalkiness formation have been reported. The functions of the genes regulating chalkiness, primarily those involved in starch synthesis, storage protein synthesis, transcription regulation, organelle development, grain shape regulation, and high-temperature response, are described. Finally, we identify the challenges associated with genetic improvement of chalkiness and suggest potential strategies. Thus, the review offers insight into the molecular dynamics of chalkiness and provides a strong basis for the future breeding of high-quality rice varieties.