Plant autophagosomes mature into amphisomes prior to their delivery to the central vacuole

Abstract

Autophagosomes are double-membraned vesicles that traffic harmful or unwanted cellular macromolecules to the vacuole for recycling. Although autophagosome biogenesis has been extensively studied, mechanisms of autophagosome maturation, i.e., delivery and fusion with the vacuole, remain largely unknown in plants. Here, we have identified an autophagy adaptor, CFS1, that directly interacts with the autophagosome marker ATG8 and localizes on both membranes of the autophagosome. Autophagosomes form normally in Arabidopsis thaliana cfs1 mutants, but their delivery to the vacuole is disrupted. CFS1's function is evolutionarily conserved in plants as it also localizes to the autophagosomes and plays a role in autophagic flux in the liverwort Marchantia polymorpha. CFS1 regulates autophagic flux by connecting autophagosomes with the ESCRT-I component VPS23, leading to the formation of amphisomes. Disrupting the VPS23-CFS1 interaction affects autophagic flux and renders plants sensitive to starvation stress. Altogether, our results reveal a deeply conserved mechanism of vacuolar delivery in plants that is mediated by amphisomes.

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

“…SH3P2 has also been shown to interact with ATG8 along with PI3P and was proposed to participate in phagophore maturation [43,44]. In good agreement with Zhao et al [34], who identified SH3P2 on the outer-surface of autophagosomes and showed an interaction between SH3P2 and CFS1, SH3P2 was also found to associate to amphisomelike structures [43]. SH3P2 was also shown to be a target of the bacterial effector protein XopL, which actively induced the degradation of SH3P2 via its E3-ligase activity and thereby dampens autophagic degradation [45].…”

“…Regarding the fact that the LE/MVB compartment is readily able to shuttle cargo to the vacuole [4], an underlying consideration is how autophagy may interplay with this pathway. Recently, it was shown in plants that autophagosome may fuse to MVBs to form 'amphisomes' [34]. This process has already been described in mammalian and yeast cells [35][36][37] but had not thoroughly been characterized in plants.…”

“…This process has already been described in mammalian and yeast cells [35][36][37] but had not thoroughly been characterized in plants. In A. thaliana, it was now shown that cell-death-related endosomal FYVE/SYLF protein 1 (CFS1, also called FYVE2) acts as an adaptor between ATG8a and the endosomal sorting complex required for transport (ESCRT)-I complex present at MVBs [10,34,38]. ESCRT complexes have been shown to be involved in autophagic turnover in other model organisms and there is now some evidence of the involvement of ESCRTs in plant autophagy, although much has yet to be discovered [27,[39][40][41].…”

Cargo receptors and adaptors for selective autophagy in plant cells

“…Selective autophagy degradation of mitochondria (mitophagy), chloroplasts (chlorophagy), peroxisomes (pexophagy), endoplasmic reticulum (reticulophagy), nuclei (nucleophagy), proteasomes (proteaphagy), ribosomes (ribophagy), aggregated proteins (aggrephagy) and pathogens (xenophagy). cell death-related endosomal FYVE/SYLF protein 1) was reported as being involved in autophagic flux in the liverwort Marchantia polymorpha by connecting autophagosomes with the ESCRT-I component VPS23, leading to the formation of amphisome [19]. The hybrid organelle (amphisome) in this case is formed by the fusion of APs with the multivesicular body before fusing with the plant vacuole [19].…”

“…Interestingly, an autophagy adaptor named CFS1 (i.e. cell death‐related endosomal FYVE/SYLF protein 1) was reported as being involved in autophagic flux in the liverwort Marchantia polymorpha by connecting autophagosomes with the ESCRT‐I component VPS23, leading to the formation of amphisome [19]. The hybrid organelle (amphisome) in this case is formed by the fusion of APs with the multivesicular body before fusing with the plant vacuole [19].…”