Antagonistic Ghd7-OsNAC42 Complexes Modulate Carbon and Nitrogen Metabolism to Achieves Superior Quality and High Yield in Rice.

Close coordination of carbon and nitrogen (C/N) metabolism is necessary to maintain optimal growth and development of plants and other cellular organisms. The central regulator for achieving high-yield and quality synergy in rice through regulating the dynamic C/N balance has seldom been reported. Here, the novel function of Grain number, plant height, and heading date7 (Ghd7) gene are reported as both a negative regulator of grain protein content and a positive regulator of rice grain quality (including appearance quality and eating quality). As a transcription factor with both activating and inhibitory functions, Ghd7 directly binds to CCACC motif genes involved in C/N metabolism. OsNAC42, an interacting protein of Ghd7, antagonistically regulates the expression of these target genes in rice seedlings and endosperm by forming a heterodimer with Ghd7. The antagonistic Ghd7-OsNAC42 module can flexibly regulate C/N metabolism in vivo in response to various nitrogen levels, thereby maintaining a dynamic C/N balance. Phenotypically, OsNAC42 enhances grain protein content but compromises quality-functions opposing Ghd7's effects. In summary, the discovery of the Ghd7-OsNAC42 antagonistic module provides new insights into the synergy between superior quality and high yield in rice.