Balanced nitrogen–iron sufficiency boosts grain yield and nitrogen use efficiency by promoting tillering

Abstract

Crop yield plays a critical role in global food security. For optimal plant growth and maximal crop yields, nutrients must be balanced. However, the potential significance of balanced nitrogen–iron (N–Fe) for improving crop yield and nitrogen use efficiency (NUE) has not previously been addressed. Here, we show that balanced N–Fe sufficiency significantly increases tiller number and boosts yield and NUE in rice and wheat. NIN-like protein 4 (OsNLP4) plays a pivotal role in maintaining the N–Fe balance by coordinately regulating the expression of multiple genes involved in N and Fe metabolism and signaling. OsNLP4 also suppresses OsD3 expression and strigolactone (SL) signaling, thereby promoting tillering. Balanced N–Fe sufficiency promotes the nuclear localization of OsNLP4 by reducing H₂O₂ levels, reinforcing the functions of OsNLP4. Interestingly, we found that OsNLP4 upregulates the expression of a set of H₂O₂-scavenging genes to promote its own accumulation in the nucleus. Furthermore, we demonstrated that foliar spraying of balanced N–Fe fertilizer at the tillering stage can effectively increase tiller number, yield, and NUE of both rice and wheat in the field. Collectively, these findings reveal the previously unrecognized effects of N–Fe balance on grain yield and NUE as well as the molecular mechanism by which the OsNLP4–OsD3 module integrates N–Fe nutrient signals to downregulate SL signaling and thereby promote rice tillering. Our study sheds light on how N–Fe nutrient signals modulate rice tillering and provide potential innovative approaches that improve crop yield with reduced N fertilizer input for benefitting sustainable agriculture worldwide.