Sculpting nuclear envelope identity from the endoplasmic reticulum during the cell cycle.

The nuclear envelope (NE) regulates nuclear functions, including transcription, nucleocytoplasmic transport, and protein quality control. While the outer membrane of the NE is directly continuous with the endoplasmic reticulum (ER), the NE has an overall distinct protein composition from the ER, which is crucial for its functions. During open mitosis in higher eukaryotes, the NE disassembles during mitotic entry and then reforms as a functional territory at the end of mitosis to reestablish nucleocytoplasmic compartmentalization. In this review, we examine the known mechanisms by which the functional NE reconstitutes from the mitotic ER in the continuous ER-NE endomembrane system during open mitosis. Furthermore, based on recent findings indicating that the NE possesses unique lipid metabolism and quality control mechanisms distinct from those of the ER, we explore the maintenance of NE identity and homeostasis during interphase. We also highlight the potential significance of membrane junctions between the ER and NE.

Mechanistic insights into an atypical interaction between ATG8 and SH3P2 in Arabidopsis thaliana.

In selective macroautophagy/autophagy, cargo receptors are recruited to the forming autophagosome by interacting with Atg8 (autophagy-related 8)-family proteins and facilitate the selective sequestration of specific cargoes for autophagic degradation. In addition, Atg8 interacts with a number of adaptors essential for autophagosome biogenesis, including ATG and non-ATG proteins. The majority of these adaptors and receptors are characterized by an Atg8-family interacting motif (AIM) for binding to Atg8. However, the molecular basis for the interaction mode between ATG8 and regulators or cargo receptors in plants remains largely unclear. In this study, we unveiled an atypical interaction mode for Arabidopsis ATG8f with a plant unique adaptor protein, SH3P2 (SH3 domain-containing protein 2), but not with the other two SH3 proteins. By structure analysis of the unbound form of ATG8f, we identified the unique conformational changes in ATG8f upon binding to the AIM sequence of a plant known autophagic receptor, NBR1. To compare the binding affinity of SH3P2-ATG8f with that of ATG8f-NBR1, we performed a gel filtration assay to show that ubiquitin-associated domain of NBR1 outcompetes the SH3 domain of SH3P2 for ATG8f interaction. Biochemical and cellular analysis revealed that distinct interfaces were employed by ATG8f to interact with NBR1 and SH3P2. Further subcellular analysis showed that the AIM-like motif of SH3P2 is essential for its recruitment to the phagophore membrane but is dispensable for its trafficking in endocytosis. Taken together, our study provides an insightful structural basis for the ATG8 binding specificity toward a plant-specific autophagic adaptor and a conserved autophagic receptor.Abbreviations: ATG, autophagy-related; AIM, Atg8-family interacting motif; BAR, Bin-Amphiphysin-Rvs; BFA, brefeldin A; BTH, benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester; CCV, clathrin-coated-vesicle; CLC2, clathrin light chain 2; Conc A, concanamycin A; ER, endoplasmic reticulum; LDS, LIR docking site; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; LIR, LC3-interacting region; PE, phosphatidylethanolamine; SH3P2, SH3 domain containing protein 2; SH3, Src-Homology-3; UBA, ubiquitin-associated; UIM, ubiquitin-interacting motif.

Plant Mitophagy in Comparison to Mammals: What Is Still Missing?

Mitochondrial homeostasis refers to the balance of mitochondrial number and quality in a cell. It is maintained by mitochondrial biogenesis, mitochondrial fusion/fission, and the clearance of unwanted/damaged mitochondria. Mitophagy represents a selective form of autophagy by sequestration of the potentially harmful mitochondrial materials into a double-membrane autophagosome, thus preventing the release of death inducers, which can trigger programmed cell death (PCD). Recent advances have also unveiled a close interconnection between mitophagy and mitochondrial dynamics, as well as PCD in both mammalian and plant cells. In this review, we will summarize and discuss recent findings on the interplay between mitophagy and mitochondrial dynamics, with a focus on the molecular evidence for mitophagy crosstalk with mitochondrial dynamics and PCD.