Ufmylation bridges autophagy and ER homeostasis in plants.

The autophagic machinery is highly conserved in eukaryotes. Plants, as sessile organisms, are more susceptible to environmental stresses than animals. Autophagy plays a pivotal role in plant stress responses, but the regulation of autophagic flux in plants remains enigmatic with few autophagic receptors identified. We recently characterized an E3 ligase, the ubiquitin-fold modifier 1 (Ufm1) ligase 1 (Ufl1), as well as its small modifier protein Ufm1, as interactors of the core autophagy-related (ATG) proteins. Mutants of these ufmylation system components are hypersensitive to salt stress and trigger the upregulation of endoplasmic reticulum (ER) stress-responsive genes, as well as the accumulation of ER sheets caused by a defect in reticulophagy. Increased expression of Ufl1, Ufm1 and Ufm1-conjugating enzyme 1 (Ufc1) are also triggered by salt stress in plants. This study identified and demonstrated the participation of ufmylation components in maintaining ER homeostasis by regulating reticulophagy under salt stress in plants.: ATG, autophagy-related; ER, endoplasmic reticulum; LIR, LC3-interacting region; ROS, reactive oxygen species; CDK5RAP3/C53, CDK5 regulatory subunit-associated protein 3; Uba5, Ufm1-activating enzyme 5; Ufc1, Ufm1-conjugating enzyme 1; Ufl1, Ufm1 ligase 1; Ufm1, ubiquitin-fold modifier 1; UPR, unfolded protein response.