Evidence of the specific roles of autophagy in senescent leaves and maturing seeds.

Abstract

In plants, a large part of the nutrients used to generate seed lipid and protein reserves is derived from both the degradation of macromolecules in source leaves and the transfer of small catabolic molecules like amino acids from the senescing leaves to the seeds. Studies of autophagy mutants in Arabidopsis showed that autophagy is a master player controlling 60% of the remobilization of nitrogen from senescing leaf tissues to developing seeds, and strongly impacting reserve deposition, especially in the protein to lipid ratio. Since autophagy is largely enhanced in leaves during senescence and in the seeds during maturation, we investigated the roles of autophagy in these sources and sink tissues, to identify checkpoints controlling seed filling and quality. Through gene complementation using tissue-specific promoters, we demonstrated that while autophagy regulates nitrogen flux to the seeds in source leaves, the autophagy taking place in seeds during their maturation is essential to reach the appropriate seed quality in terms of C and N storage. Overall, these results highlight the multiple roles of autophagy in the optimal development of the plant throughout its entire lifespan.