Unlocking G-protein subunit GS3: How Redox Regulation Shapes Grain Size

In a recent study by researchers from Prof. LI Yunhai’s lab at the Institute of Genetics and Developmental Biology (IGDB) of the Chinese Academy of Sciences (CAS), a hidden mechanism controlling rice grain size, a critical factor in crop productivity, has been revealed. Published in The EMBO Journal (https://doi.org/10.1038/s44318-025-00462-9), the study unveils how rice plants utilize chemical "switches" and molecular "scissors" to regulate grain size.

 

Grain size plays a direct role in rice yield and quality. Scientists have long known that a protein named GS3 acts as a "brake" on grain elongation. Naturally occurring mutations in GS3 that weaken its function are commonly utilized in breeding programs to cultivate longer grains. However, the regulation of GS3 activity has remained unclear.

 

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.

 

Enter WG1, a glutaredoxin enzyme that reshapes this system. Operating as molecular scissors, WG1 breaks the disulfide bonds that hold GS3 clusters together. This redox-dependent process transforms clustered GS3 into active single molecules, restoring their ability to limit grain elongation.

 

The cystein-rich tail of GS3 drives cluster formation, elucidating why natural variants with shortened tails result in significantly shorter grain size.

 

This discovery connects redox biology with agricultural science. Lead researcher Prof. LI Yunhai remarks, "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."

 

Contact:

Prof. LI Yunhai

Institute of Genetics and Developmental Biology, Chinese Academy of Sciences

Email: yhli@genetics.ac.cn