Abstract
Autophagy is essential for nutrient recycling and plays a fundamental role in seed production and grain filling in plants. Autophagy participates in nitrogen remobilization at the whole-plant level, and the seeds of autophagy mutants present abnormal C and N contents relative to wild-type (WT) plants. It is well known that autophagy (ATG) genes are induced in leaves during senescence; however, expression of such genes in seeds has not yet been reported. In this study we show that most of the ATG genes are induced during seed maturation in Arabidopsis siliques. Promoter-ATG8f::UIDA and promoter-ATG8f::GFP fusions showed the strong expression of ATG8f in the phloem companion cells of pericarps and the funiculus, and in the embryo. Expression was especially strong at the late stages of development. The presence of many GFP-ATG8 pre-autophagosomal structures and autophagosomes confirmed the presence of autophagic activity in WT seed embryos. Seeds of atg5 and WT plants grown under low- or high-nitrate conditions were analysed. Nitrate-independent phenotypes were found with higher seed abortion in atg5 and early browing, higher total protein concentrations in the viable seeds of this mutant as compared to the WT. The higher total protein accumulation in atg5 viable seeds was significant from early developmental stages onwards. In addition, relatively low and early accumulation of 12S globulins were found in atg5 seeds. These features led us to the conclusion that atg5 seed development is accelerated and that the protein storage deposition pathway is somehow abnormal or incomplete.
Highlights
Macroautophagy is a universal degradation mechanism that facilitates the clearing of unwanted constituents from eukaryotic cells
The relative expression of almost all the ATG genes increased during seed development and especially during maturation
Three genes showed decreased expression during silique development, namely ATG1c and ATG13a that belong to the AT1/ATG13 complex, which plays a role in the induction of the autophagy process, and ATG4b that is involved in the ATG8 conjugation system
Summary
Macroautophagy (hereafter termed autophagy) is a universal degradation mechanism that facilitates the clearing of unwanted constituents from eukaryotic cells. ATG5 gene is a unique copy gene in all animal and plant species studied so far It is involved in the ATG5–ATG12 conjugation system that is essential for the formation of the ATG8–PE (phosphatidylethanolamine) conjugate that characterizes the autophagosome membrane (Yoshimoto et al, 2004). Transcriptome data that can be consulted on public databases such as the BAR (http://bar.utoronto.ca) or Genevestigator (https://genevestigator.com/gv/) sites shows that most of the Arabidopsis ATG genes are up-regulated in rosettes with ageing and in seeds during development. This led us to hypothesize that autophagy could play a physiological role in the seed, independently of its role in the mother plant
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