A molecular framework underlying low-nitrogen- induced early leaf senescence in Arabidopsis thaliana

Nitrogen (N) deficiency causes early leaf senescence, resulting in accelerated whole-plant maturation and severely reduced crop yield. However, the molecular mechanisms underlying N-deficiency-induced early leaf senescence remain unclear, even in the model species Arabidopsis thaliana. In this study, we identified Growth, Development and Splicing 1 (GDS1), a previously reported transcription factor, as a new regulator of nitrate (NO3-) signaling by a yeast-one-hybrid screen using a NO3- enhancer fragment from the promoter of NRT2.1. We showed that GDS1 promotes NO3- signaling, absorption and assimilation by affecting the expression of multiple NO3- regulatory genes, including Nitrate Regulatory Gene2 (NRG2). Interestingly, we observed that gds1 mutants show early leaf senescence as well as reduced NO3- content and N uptake under N-deficient conditions. Further analyses indicated that GDS1 binds to the promoters of several senescence-related genes, including Phytochrome-Interacting Transcription Factors 4 and 5 (PIF4 and PIF5) and represses their expression. Interestingly, we found that N deficiency decreases GDS1 protein accumulation, and GDS1 could interact with Anaphase Promoting Complex Subunit 10 (APC10). Genetic and biochemical experiments demonstrated that Anaphase Promoting Complex or Cyclosome (APC/C) promotes the ubiquitination and degradation of GDS1 under N deficiency, resulting in loss of PIF4 and PIF5 repression and consequent early leaf senescence. Furthermore, we discovered that overexpression of GDS1 could delay leaf senescence and improve seed yield and N-use efficiency (NUE) in Arabidopsis. In summary, our study uncovers a molecular framework illustrating a new mechanism underlying low-Ninduced early leaf senescence and provides potential targets for genetic improvement of crop varieties with increased yield and NUE.