WHITE-CORE RATE 1 regulates grain chalkiness in rice

Wu et al. uncover a mechanism underlying chalkiness, an important grain quality trait in rice.

Background: With improved living standards, the demand for better grain quality has become a challenge in rice production areas. Rice chalkiness, i.e., endosperm containing opaque regions, seriously reduces the appearance quality of grain, making it unpopular for consumers and marketers. Gene cloning and molecular breeding have become important techniques for improving rice quality, but the improvement of chalkiness still faces many problems, including the scarcity of excellent alleles and unclear molecular mechanisms. Reactive oxygen species (ROS) play important roles in the formation of chalkiness. However, it is unclear which molecules are involved in this process.

Question: We wanted to identify the chalkiness gene by map-based cloning, analyze its natural variation, and find useful alleles. We also wondered what role this gene plays in the formation of chalkiness.

 Findings: We cloned the rice chalkiness gene WCR1 (WHITE-CORE RATE 1), encoding an F-box protein that negatively regulates grain chalkiness. A functional A/G variation in the promoter region of WCR1 affects the binding of the transcriptional activator OsDOF17 to its promoter. We propose a model for the role of WCR1 in regulating chalkiness in which WCR1 promotes the elimination of excess ROS, maintains redox homeostasis, and delays programmed cell death in starchy endosperm by positively affecting the transcription of the metallothionein gene MT2b and suppressing the 26S proteasome-mediated degradation of MT2b.

Next steps: We will focus on the precise mechanism underlying the role of WCR1 in regulating MT2b transcription and the protein level of MT2b. We are also interested in using WCR1 to improve rice grain quality.

Bian Wu, Peng Yun, Hao Zhou, Duo Xia, Yuan Gu, Pingbo Li, Jialing Yao, Zhuqing Zhou, Jianxian Chen, Rongjia Liu, Shiyuan Cheng, Hao Zhang, Yuanyuan Zheng, Guangming Lou, Pingli Chen, Shanshan Wan, Mingsong Zhou, Yanhua Li, Guanjun Gao, Qinglu Zhang, Xianghua Li, Xingming Lian, and Yuqing He (2022). Natural variation in WHITE-CORE RATE 1 regulates redox homeostasis in rice endosperm to affect grain quality. https://doi.org/10.1093/plcell/koac057