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.
In this study, the biosynthesis of microcystins (MCs) was investigated after long-term nitrogen-starved conditions in cyanobacterium Microcystis aeruginosa . The results demonstrated that the algal cells were able to survive in a non-growing state with nitrogen starvation for more than one month. The physiological properties of the algal cells were studied to elucidate the mechanisms of viability under nitrogen-deprivation conditions. After the state of nitrogen chlorosis, new toxins could be resynthesized and tracked using 15 N-stable isotope-labelled nitrogen. Nitrogen starvation of nutritionally replete cells resulted in a significant increase of microcystin-LY (MC-LY), thereby suggesting that MC-LY may undergo catabolism to provide nitrogen or that MC-LY may be produced to play an important role in the cell in response to nitrogen deprivation. The rank order of different types of nitrogen in algal cells assimilation was N-ammonium > N-urea > N-nitrate > N-alanine. The relationship between the production of toxin variants and various environmental conditions is an interesting issue for future research and may help improve the understanding of the ecological role of cyanobacterial toxins .
危险品化学品经营许可证（带存储）