Autophagy Controls Sulphur Metabolism in the Rosette Leaves of Arabidopsis and Facilitates S Remobilization to the Seeds.

Sulphur deficiency in crops became an agricultural concern several decades ago, due to the decrease of S deposition and the atmospheric sulphur dioxide emissions released by industrial plants. Autophagy, which is a conserved mechanism for nutrient recycling in eukaryotes, is involved in nitrogen, iron, zinc and manganese remobilizations from the rosette to the seeds in . Here, we have compared the role of autophagy in sulphur and nitrogen management at the whole plant level, performing concurrent labelling with S and N isotopes on mutants and control lines. We show that both S and N remobilizations from the rosette to the seeds are impaired in the mutants irrespective of salicylic acid accumulation and of sulphur nutrition. The comparison in each genotype of the partitions of N and S in the seeds (as % of the whole plant) indicates that the remobilization of S to the seeds was twice more efficient than that of N in both autophagy mutants and control lines under high S conditions, and also in control lines under low S conditions. This was different in the autophagy mutants grown under low S conditions. Under low S, the partition of S to their seeds was indeed not twice as high but similar to that of N. Such discrepancy shows that when sulphate availability is scarce, autophagy mutants display stronger defects for S remobilization relative to N remobilization than under high S conditions. It suggests, moreover, that autophagy mainly affects the transport of N-poor S-containing molecules and possibly sulphate.