OsSIZ1 regulates rice nitrogen-use efficiency and grain yield by modulating auxin levels

Auxin plays a pivotal role in regulating crop nitrogen (N)-use efficiency (NUE), coordinating both N-responsive root development and the expression of N metabolism genes. In our previous work, we identified DULL NITROGEN RESPONSE1 (DNR1) as a repressor within the auxin-mediated NUE network in rice. Here, we further delineate this pathway by identifying the SUMO E3 ligase OsSIZ1 as a key upstream regulator of DNR1. Contrary to its canonical role, we discovered that OsSIZ1 exhibits ubiquitin E3 ligase activity toward DNR1, facilitating its polyubiquitination at lysine 314 and subsequent degradation. This degradation promotes auxin accumulation, thereby enhancing NUE and grain yield. Notably, the yield advantage driven by OsSIZ1 is most pronounced under low-N conditions, underscoring its potential as a breeding target for developing resilient crops that require less N fertilizer, enabling a more sustainable agriculture.