The E3 ubiquitin ligase SCFLAO1 promotes NITRITE REDUCTASE degradation to modulate growth and oilseed production in Brassica napus

Abstract

Efficient nitrogen utilization is essential for the survival and yield improvement of rapeseed (Brassica napus L.), an important oil crop. However, the mechanisms governing nitrogen responses and use efficiency in this species remain poorly understood. In this study, we identify BnLAO1 genes as repressors of nitrogen-stimulated growth and oilseed production in B. napus. BnLAO1 genes encode F-box proteins that associate with CULLIN1 (BnCUL1) to form intact SKP1/CULLIN/F-box (SCF) E3 ubiquitin ligases. BnLAO1 proteins are regulated by the autophagy pathway through their direct interaction with BnATG8A. Furthermore, we provide evidence that BnLAO1 proteins directly interact with and degrade NITRITE REDUCTASE (BnNiR), a pivotal enzyme in nitrogen assimilation. Interestingly, the homologue of BnLAO1 proteins in Arabidopsis, AtLAO1, does not interact with or degrade AtNiR. Finally, we demonstrate that the functional differences between BnLAO1 proteins and AtLAO1 are due to two amino acid mutations in BnNiR, which influence NiR recognition by LAO1 in plants. Collectively, this study elucidates BnLAO1 function within the regulatory network governing nitrogen utilization in B. napus, offering valuable insights for developing nitrogen-efficient crop varieties.