Sun Jiaqi, Wang Weina, Zheng Huanquan
Department of Biology, McGill University, Montreal, QC, Canada.
Front Plant Sci. 2022 Feb 24;13:817251. doi: 10.3389/fpls.2022.817251. eCollection 2022.
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 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 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 .
根毛缺陷3（RHD3）是atlastin GTP酶家族的植物成员，atlastin GTP酶属于一个进化上保守的蛋白质家族，介导内质网（ER）的同型融合。最近研究表明，哺乳动物细胞中的一种atlastin在营养饥饿期间作为内质网自噬（ER自噬）选择性自噬的内质网自噬受体发挥作用。尽管已表明RHD3在ER应激反应中起作用，但RHD3如何参与该过程尚不清楚。在本研究中，我们发现该突变体对ER和盐胁迫均不敏感。我们使用了一个带有黄色荧光蛋白（YFP）标记的内质网膜标记物YFP-TMC，通过显微镜和生化方法监测ER自噬的效率。我们发现该突变体在ER应激下的ER自噬存在缺陷。此外，YFP-RHD3与ATG8e标记的自噬体的结合增加。YFP-RHD3在液泡中也与ATG8e可见，并且在ER应激下YFP-RHD3会降解。RHD3有两个假定的ATG8相互作用基序（AIM1-2）。我们发现RHD3而非RHD3（ΔAIM1）与ATG8发生物理相互作用，ATG8是自噬体的核心成分，它与各种受体蛋白相互作用，通过选择性自噬募集货物进行降解。此外，它们的相互作用在ER应激下增强。因此，我们提出RHD3在ER应激下作为ER自噬受体，促进该突变体中的ER自噬。
