Autophagy and plant proteases for nutrient remobilization during leaf senescence
Résumé
Senescence is a long developmental process dedicated to the shift from primary nitrogen and carbon assimilation to progressive cell-constituent degradation. Catabolism events occurring during leaf senescence are dedicated to nutrient recycling and remobilization at the whole plant level. Autophagy is enhanced during developmental leaf senescence and even more severely when nutrient limitation is applied. Autophagy mutants are strongly impaired in the remobilization of nitrogen from the rosettes to the seeds, especially when cultivated under low nitrate conditions. Autophagy machinery involves up to 40 ATG proteins in Arabidopsis. In order to stimulate autophagy in Arabidopsis we overexpressed one of them and showed that overexpression of ATG8 increases autophagic activity and N remobilization efficiency Autophagy mutants, that cannot recycle and remobilize nitrogen, accumulate numerous protease activities amongst which several well-known cysteine proteases. The protease activities stimulated in autophagy mutants may compensate the weaknesses of mutants in N-recycling. In order to investigate the alternative degradation pathways enhanced in autophagy defective mutants, nitrogen remobilization was monitored in-in chosen protease mutants using 15N tracing. An overview of all the senescence-related nitrogen remobilization mechanisms studied in our laboratory, amongst which autophagy pathway will be presented integrating the recent results obtained.