A research team led by Prof. Li Yunhai from the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences has uncovered a previously hidden mechanism that regulates rice grain size—a key determinant of crop yield and quality.

The findings, published in The EMBO Journal, reveal how redox-dependent molecular interactions act as “switches” and “scissors” to fine-tune grain development.

Rice grain size directly impacts both productivity and market value, and the protein GS3 has long been known to suppress grain elongation. Natural mutations that reduce GS3 activity have been widely adopted in rice breeding to produce longer grains. However, the precise molecular mechanism controlling GS3 function had remained elusive until now.

The research team has found that GS3 forms molecular clusters (oligomers) through disulfide bonds—a chemical linkage between sulfur atoms in proteins. These clusters diminish GS3’s capacity to interact with another growth-regulating protein (G-protein subunit RGB1), thereby weakening its restriction on grain elongation.

The researchers identified a glutaredoxin enzyme named WG1 as the molecular “scissors” in this system. WG1 cleaves the disulfide bonds holding the GS3 clusters together, converting them back into monomers—single, active molecules capable of restraining grain elongation. This redox-sensitive transformation highlights a dynamic regulatory system governed by cellular oxidative conditions.

The researchers also found that the cysteine-rich C-terminal region of GS3 is essential for cluster formation, explaining why natural GS3 variants with truncated tails lead to shorter grains.

This discovery connects redox biology with agricultural science. “This is the first demonstration of redox regulation in plant G-protein signaling. It paves the way for manipulating protein interactions through redox engineering.

“Targeting gene editing of GS3’s cysteine-rich region could enable precise adjustments in grain length—a promising strategy for future ‘designer rice’ with potential benefits for various crops,” said Prof. Li Yunhai, lead researcher of the study.