AAD modulates rice yield through purine nitrogen remobilization
Rice yield is determined by critical agronomic traits including grain filling and tiller number, which are linked to nitrogen metabolism. While glutamine synthetase-glutamate synthase (GS-GOGAT) mediated N assimilation is well studied, the role of purine catabolism in rice nitrogen remobilization remains unclear. Here, we cloned the gene OsAAD, which encodes allantoate amidohydrolase, a key enzyme in purine catabolism, localized to the endoplasmic reticulum. OsAAD loss-of-function (CRISPR-Cas9) mutants accumulated allantoate but showed reduced NH4+ in developing grains, impairing N remobilization. This disrupted the GS-GOGAT cycle and tricarboxylic acid flux, causing ATP deficiency that hindered sucrose-to-starch conversion and reduced starch content. Concurrently, osaah mutants accumulated lower NH4+ in tiller buds, upregulating the tillering inhibitor OsTCP19 and suppressing bud outgrowth. Conversely, OsAAD overexpression increased tiller number and grain yield. Additionally, transcription factor ERF3 directly binds the OsAAD promoter to activate its expression. erf3 mutants exhibited similar phenotypes to osaah mutants, including defective grain filling, and accumulated allantoate content. Our findings demonstrate that the ERF3-OsAAD module coordinates purine nitrogen remobilization to optimize grain filling and tillering. This reveals a dual mechanism for yield enhancement and provides novel targets for improving rice productivity.