ROOT HAIR DEFECTIVE3 Is a Receptor for Selective Autophagy of the Endoplasmic Reticulum in Arabidopsis

Abstract

ROOT HAIR DEFECTIVE3 (RHD3) is a plant member of atlastin GTPases, which belong to an evolutionally conserved family of proteins that mediate the homotypic fusion of the endoplasmic reticulum (ER). An atlastin in mammalian cells has recently been shown to act as an ER-phagy receptor for selective autophagy of the ER (ER-phagy) during nutrient starvation. Although RHD3 has been indicated to play a role in ER stress response, it is not very clear how RHD3 is involved in the process. In this study, we showed that the rhd3 mutant is hyposensitive to ER as well as salt stress. We employed an YFP-tagged ER membrane marker YFP-TMC to monitor the efficiency of ER-phagy microscopically and biochemically. We found that rhd3 is defective in ER-phagy under ER stress. Furthermore, there is an increased association of YFP-RHD3 with ATG8e-marked autophagosomes. YFP-RHD3 is also visible with ATG8e in the vacuole, and there is a breakdown of YFP-RHD3 under ER stress. RHD3 has two putative ATG8 interaction motifs (AIM1-2). We revealed that RHD3 but not RHD3(ΔAIM1) physically interacts with ATG8, a core autophagosomal component that interacts with various receptor proteins to recruit cargos for degradation by selective autophagy. Furthermore, their interaction is enhanced under ER stress. We thus propose that RHD3 acts as an ER-phagy receptor under ER stress to promote ER-phagy in Arabidopsis.

Hydrogen sulfide action in the regulation of plant autophagy

“…Three other receptors have been identified in yeast, Atg39 and Atg40 [64] and Epr1 [65]. Several studies in plants have led to deciphering two more receptors for ER‐phagy, ATI1 and ATI2 [66], and more recently, a new receptor cross‐kingdom has been described in plants, Arabidopsis Sec62 (AtSec62) [67], and the root hair defective3 (RHD3) receptor too [68]. In addition, mammalian C53 protein, also found in plants, has also been identified as an ER‐phagy receptor, which does not behave as other receptors interacting with ATG8 directly through its AIM region, it interacts with ATG8 by a non‐canonical AIM instead [69].…”

Autophagic degradation of membrane-bound organelles in plants

“…ER-phagy relies on specific receptor–adaptor interactions to facilitate engulfment of ER fragments by autophagosomes or direct delivery to the vacuole. To date, many ER-phagy receptors were identified and characterized in eukaryotes, including FAM134, Sec62, RTN3, CCPG1, ATL3, TEX264, CALCOCO1 and C53 in mammals [ 13 ]; Atg39, Atg40, and Epr1 in yeast [ 13 ]; and ATI1, ATI2, ATI3, RTN1, RTN2, AtSEC62, C53 and RHD3 in plants [ 13 , 24 ]. Different receptors can perceive distinct signals to control the degradation of ER fragments ( Figure 2 ), indicating their functional diversification in ER-phagy.…”

“…Arabidopsis ROOT HAIR DEFECTIVE (RHD) 3 is an atlastin GTPase previously reported to be involved in root development [ 31 ], and more recently identified as an ER-phagy receptor [ 24 ]. The orthologs of RHD3 in mammals, atlastin 2 (ATL2) and 3 (ATL3), were reported to play an important role in ER-phagy [ 32 , 33 ].…”

“…Two distinct AIM sites were identified on RHD3, but interestingly, only AIM2 is involved in the interaction with ATG8, and ER stress treatments enhance the interaction between RHD3 and ATG8. Sun et al [ 24 ] further showed that an rhd3 mutant is sensitive to ER stress and deficient in ER-phagy.…”

Crossing paths: recent insights in the interplay between autophagy and intracellular trafficking in plants

“…This interaction was shown to increase during ER stress (here dithiothreitol or tunicamycin treatments), suggesting the importance of reticulon proteins for the maintenance ER homeostasis [18]. The atlastin GTPase root hair deffective 3 has also been demonstrated as being an ER‐localized autophagy receptor involved in ER‐phagy induced by ER stress [19].…”