Trouverie, J. | bioRxiv Science

bioRxiv2024

Multi-scale phenotyping of senescence-related changes in roots of rapeseed in response to nitrogen deficiency

Senescence related markers have been widely studied in leaves in many plant species. Root senescence is more difficult to characterize. The existence of two different root organs in B. napus, with a taproot that appear to be specifically dedicated to the storage and remobilization of nutrients, offered the possibility of analysing the temporality of the changes linked to aging, based on the degradation of the taproot reserves. Microscopic and biochemical analyses showed that taproot plays an important role in carbon and nitrogen storage as reflected by the large quantities of starch and proteins present at early development stages. The proteomic study associated to the description of biochemical, morphological and anatomic changes provides a comprehensive picture of the main events occurring in the taproot and in the lateral roots with aging. Master modifications as protein and cell wall degradation, amino acid catabolism versus synthesis, nucleic acid degradation are presented and senescence related markers specific or not of the root types were identified. Comparison with Arabidopsis public data facilitated the identification of markers common to root and leaf senescence. The analysis of protease changes provides a list of candidates that may play a role in nitrogen and carbohydrate remobilization from taproot to the shoot and flowering organs and that would deserve attention for further functional analyses.

plant biology↗

bioRxiv2023

Autophagic activity acts as a rheostat in the control of nitrogen transfer from Arabidopsis rosette leaves to the seeds according to a principle of communicating vessels

Macroautophagy is known for long as essential for the degradation and the recycling of different macromolecules in eukaryotes. However how important is autophagy for nitrogen management at the whole plant level and for plant biomass and yield productivity in unstressed and well feed plants needed further investigation. In this study, we used both autophagy knock-out mutants and autophagy over-expressors that constitutively produce numerous autophagosomes. These mutants and over-expressors were cultivated using hydroponic system to observe and compare their phenotypes under sufficient nitrate supply, and when submitted after a while to strict nitrate starvation. The shift from nitrate sufficient condition to nitrate starvation allowed us to determine how autophagy defective or stimulated lines can use their own nitrogen resources to complete their cycle. Unexpectedly we observed that irrespective of the nitrate conditions, both mutants and over-expressors exhibited early leaf senescence phenotypes relative to wild type. While autophagy mutants exhibited strong defect for N remobilisation and seed production irrespective of nitrate condition, the better performance of autophagy-over expressors for N remobilisation and seeds production was only significant under sufficient nitrate supply, i.e. when autophagy was not naturally stimulated by nitrate limitation. Interestingly, comparisons of genotypes showed that the nitrogen pool used for seed filling originated from rosette leaves, as if rosette and seeds were used as communicating vessels independently of the stem and pod connecting organs. Altogether, results show that autophagy is a master player in nitrogen management at the whole plant level that controls yield production and leaf senescence.

physiology↗