OsGAT2 modulates nitrogen allocation and heading date in rice through amino acid transport

Heading date (or flowering time) is one of the most important agronomic traits in rice, as it determines regional adaptability and grain yield. Its regulation is influenced by multiple factors, including photoperiod, nutritional status, and endogenous phytohormones. However, the roles of amino acids and their transporters in regulating heading date remain largely unclear. In this study, we identified four haplotypes in the promoter region of the rice amino acid transporter gene OsGAT2 among diverse germplasm resources. Haplotypes associated with lower OsGAT2 expression exhibited earlier heading date, longer grain length, and reduced nitrogen content. Further analyses showed that OsGAT2 is mainly expressed in basal tissues, stems, and leaf sheaths, and is localized to the plasma membrane. Substrate assays in yeast demonstrated that OsGAT2 is capable of transporting multiple amino acids, including GABA, Ser, Leu, Glu, Val, Gly, and Ala. Functional analyses revealed that knockout of OsGAT2 promoted earlier heading date, whereas overexpression lines exhibited delayed heading date. Consistently, the contents of GABA, several amino acids, and total nitrogen in the leaves and panicles were significantly higher in OsGAT2 overexpression lines than in the wild-type, whereas OsGAT2 CRISPR knockout lines exhibited tissue-dependent changes, with increased stem nitrogen content but reduced nitrogen content in leaves and panicles. Moreover, exogenous application of these amino acids further enhanced the delayed heading date phenotype in overexpression lines, while mutants headed earlier than the wild-type. Transcriptome analysis revealed that altered expression of OsGAT2 affects the regulatory network controlling heading date. The heading repressors Ghd7 and Ghd8 were significantly upregulated in OsGAT2 overexpression lines but downregulated in mutants. In contrast, heading-promoting genes, including OsGI, Hd17, and Ehd2, were markedly upregulated in the mutants. Taken together, these results demonstrate that the amino acid transporter OsGAT2 regulates rice heading date by mediating amino acid transport and modulating the expression of key heading regulatory genes. This study provides important insights and potential targets for shortening heading time and improving regional adaptability of rice through gene editing. KEY MESSAGE : The amino acid transporter gene OsGAT2 regulates rice heading date by modulating amino acid transport and the expression of heading date-related genes, thereby improving regional adaptability.