Nitrogen (N), one of the most important plant nutrients, plays crucial roles in multiple plant developmental processes. Spikelets are the primary sink tissues during reproductive growth, and N deficiency can cause floral abortion. However, the roles of N nutrition in meiosis, the crucial step in plant sexual reproduction, are poorly understood. Here, we identified an N-dependent meiotic entrance mutant with loss of function of ELECTRON TRANSFER FLAVOPROTEIN SUBUNIT β (ETFβ) in rice (Oryza sativa). etfβ displayed meiosis initiation defects, excessive accumulation of branched-chain amino acids (BCAAs) and decrease in total N contents in spikelets under N starvation, which were rescued by applying excess exogenous inorganic N. Under N starvation, ETFβ, through its involvement in BCAA catabolism, promotes N reutilization and contributes to meeting N demands of spikelets, highlighting the impact of N nutrition on meiosis initiation. We conclude that N nutrition contributes to plant fertility by affecting meiosis initiation.

Summary The endonuclease methyl methanesulfonate and UV‐sensitive protein 81 (MUS81) has been reported to participate in DNA repair during mitosis and meiosis. However, the exact meiotic function of MUS81 in rice remains unclear. Here, we use a combination of physiological, cytological, and genetic approaches to provide evidence that MUS81 functions in atypical recombination intermediate resolution rather than crossover designation in rice. Cytological and genetic analysis revealed that the total chiasma numbers in mus81 mutants were indistinguishable from wild‐type. The numbers of HEI10 foci (the sites of interference‐sensitive crossovers) in mus81 were also similar to that of wild‐type. Moreover, disruption of MUS81 in msh5 or msh4 msh5 background did not further decrease chiasmata frequency, suggesting that rice MUS81 did not function in crossover designation. Mutation of FANCM and ZEP1 could enhance recombination frequency. Unexpectedly, chromosome fragments and bridges were frequently observed in mus81 zep1 and mus81 fancm, illustrating that MUS81 may resolve atypical recombination intermediates. Taken together, our data suggest that MUS81 contributes little to crossover designation but plays a crucial role in the resolution of atypical meiotic intermediates by working together with other anti‐crossover factors.