NBR1, a plant selective autophagy receptor, associates with lipid droplets in germinating seeds and contributes to seed longevity
Résumé
NBR1, a plant selective autophagy receptor, associates with lipid droplets in germinating seeds and contributes to seed longevity
Bouchez-Mahiout I., Deruyffelaere C, Salis V, Rajou L, Collet B, Masclaux-Daubresse C, Marmagne A and D’Andrea S.
Université Paris-Saclay, INRAE, AgroParisTech, Institut Jean-Pierre Bourgin (IJPB) 78000, Versailles, France
Corresponding author: Isabelle.bouchez@inrae.fr
Plant Neighbor of BRCA1 (NBR1) is a functional hybrid of the mammalian selective autophagy receptors NBR1 and p62/SQSTM1. In Arabidopsis thaliana plantlets, NBR1 is mainly involved in aggrephagy upon heat stress. In germinated seeds, few data are available. Thus, we aimed to characterize the effect of accelerated aging on the germination capacity of nbr1 mutant seeds. Likewise, we investigated the role, expression and sub-cellular localization of NBR1 during seed germination.
We demonstrated that NBR1 deficiency is associated with a drastic reduction of germination capacity after seed accelerated aging, suggesting a specific role of NBR1 in the clearance of damaged proteins during germination. Consistently, we showed that NBR1 accumulates during seed stratification and is degraded during germination. Using subcellular fractionation, we demonstrated that NBR1 is mainly associated with lipid droplets (LD). This localization was confirmed by confocal microscopy, showing that mCherry-NBR1 surrounds many LDs and partially co-localizes with GFP-ATG8f. Nevertheless, the association of NBR1 with LDs is not dependent on ATG8, and reciprocally. In nbr1 mutant, we observed the accumulation of ubiquitinated LD proteins, suggesting that NBR1 could be involved in the degradation of LD proteins. Moreover, by exploring NBR1 degradation during germination, we showed that NBR1 could be involved in the proteasomal degradation pathway rather than in the autophagic one.
Overall, NBR1 is the first selective autophagy receptor identified as being associated with LDs in plants. However, our data suggest that NBR1 is not involved in the autophagy degradation of LDs (lipophagy) in germinating seeds, but rather in the turnover of LD proteins.