DSK2-mediated degradation of F-box protein LAO1 and class I TCPs modulates the nitrogen starvation response

Plants have evolved intricate strategies to cope with various abiotic stresses. Ubiquitin-mediated protein degradation plays a key role in plant development as well as abiotic stress tolerance. In this study, we identify LAO1, an F-box protein with unknown function, as a negative regulator of plant fitness during nitrogen starvation. DOMINANT SUPPRESSOR OF KAR 2 (DSK2) interacts with and mediates the autophagic degradation of LAO1 protein during nitrogen starvation. The loss of LAO1 improves the fitness of an autophagy-deficient mutant, atg5-1, under nitrogen starvation. Intriguingly, mutations in DSK2 facilitate rather than reduce plant growth after nitrogen starvation. This unexpected effect of DSK2 knockout led us to discover that DSK2 also interacts with and degrades a group of class I TCP transcription factors. Phenotypic observations demonstrate that class I TCPs are crucial for plant adaptation to nitrogen starvation. Moreover, genetic analyses indicate that class I TCPs function downstream of LAO1 and counteract its negative effects. Collectively, our findings unveil a previously undescribed regulatory network governing plant fitness during nitrogen starvation.