A study published in Science China Life Sciences by Zheng-Yi Xu’s group at Northeast Normal University proposes a novel regulatory model for rice grain chalkiness centered on the OsMADS18-OsbZIP60 transcriptional module, offering new genetic insights into this trait.
Rice is a globally important food crop, and grain chalkiness is a key trait that severely affects the appearance and market value of rice. However, its genetic mechanisms remain incompletely understood. To identify genetic loci regulating grain chalkiness, researchers performed high-throughput activation tagging-based T-DNA insertion mutagenesis in the model rice variety ( Oryza sativa L.) Kitaake. They found that a loss-of-function mutation in OsMADS18 resulted in enhanced grain chalkiness, reduced plant height, and delayed flowering time.
Through yeast two-hybrid (Y2H) screening, researchers identified OsbZIP60 as an interacting partner of OsMADS18. Further analysis revealed that OsMADS18 directly bound to and positively regulated the expression of chalkiness-related genes, including Chalk5 , FLO7 , OsPK2 , and OsNF-YB1 , which are also transcriptional targets of OsbZIP60. Genetic analysis revealed that the osbzip60-1 osmads18-1 double mutant phenocopied the chalkiness of osbzip60-1 , with more severe defects than osmads18-1 , placing OsbZIP60 downstream of OsMADS18 in grain chalkiness control.
Additionally, OsMADS18 positively regulates grain weight, starch content, amylose content, and protein levels under high-temperature conditions by modulating the expression of unfolded protein response (UPR) genes, including OsbZIP50 , OsBiP1 , OsBiP2 , OsBiP3 , OsBiP4 , and OsBiP5 .
These findings indicate that OsMADS18-mediated UPR, enhanced by its interaction with OsbZIP60, is critical for mitigating grain chalkiness under stress. Researchers propose a novel model wherein the OsMADS18–OsbZIP60 transcriptional module centrally governs this trait in rice.
Science China Life Sciences