The Plant ATG8-binding Proteins / 生物化学与生物物理进展

ABSTRACT

ATG8-binding proteins play a key role in autophagy, selective autophagy or non-autophagy process by interacting between ATG8 and the ATG8-interacting motif (AIM) or the ubiquitin-interacting motif (UIM). There is great progress of ATG8-binding proteins in yeast and mammalian studies. However, the plant domain is still lagging behind. Therefore, the structure characteristics of plant ATG8 binding protein were firstly outlined. Unlike the single copy of ATG8 gene in yeast, many homologous genes have been identified in plant. The LIR/ AIM-docking site (LDS) of ATG8 protein contains W and L pockets and is responsible for binding to AIM. The ATG8 protein binds to UIM-containing proteins via UIM-docking site (UDS) instead of LDS. UDS is in the opposite position to LDS, so the ATG8 can bind both AIM and UIM proteins. Secondly, the structure and function of ATG8-binding proteins, especially the selective autophagy receptors, were systematically described. The protein NBR1 and Joka2, as proteaphagy receptors, guide ubiquitination protein aggregates to autophagosome for degradation by binding to AIM and ATG8 in Arabidopsis and tobacco, respectively. AtNBR1 also promotes plant immunity by binding the capsid protein of cauliflower mosaic virus and silencing suppressor HCpro of turnip mosaic virus, mediating pathogen autophagy. AtNBR1 still degrades chloroplast by microautophagy under photoinjure or chlorophagy during ibiotic stress. And the protein ORM mediates the degradation of plant immune receptor flagellin sensing 2 (FLS2) through AIM binding to ATG8. Interestingly, ATI1 and ATI2 participate in both chlorophagy and ERphagy. Otherwise, ER membrane protein AtSec62, soluble protein AtC53, and ubiquitin-fold modifier1-specific ligase 1 (UFL1) can be directly bound to ATG8 as ER autophagy receptors. As pexophagy receptor, AtPEX6 and AtPEX10 bind to ATG8 via AIM and participate in pexophagy. RPN10, as a 26S proteasome subunit, whose C-terminal UIM1 and UIM2 bind ubiquitin and ATG8, respectively, mediates the selective autophagy degradation of 26S proteasome inactivation when fully ubiquitinated. Plant-specific mitochondrial localization proteins FCS-like zinc finger (FLZ) and friendly (FMT) may also be mitophagy receptors. CLC2 binds to ATG8 via the AIM-LDS docking site and is recruited to autophagy degradation on the Golgi membrane. The tryptophan-rich sensory protein (TSPO) in Arabidopsis was involved in clearing free heme, porphyrin and plasma membrane intrinsic protein 2;7 (PIP2;7) through the combination of AIM and ATG8. The conformation of GSNOR1 changes during anoxia, exposing the interaction between AIM and ATG8, leading to selective degradation of GSNOR1. At last, the ATG8 binding proteins involved in autophagosome closure, transport and synthetic synthesis was summarized. For example, plant-specific FYVE domain protein required for endosomal sorting 1 (FREE1) is involved in the closure of autophagosomes during nutrient deficiency. Therefore, according to the recent research advances, the structure and function of plant ATG8-binding proteins were systematically summarized in this paper, in order to provide new ideas for the study of plant selective autophagy and autophagy.