Biology subjects

Vetrano, P.

Publications and source records attributed to Vetrano, P..

4 recordsLinked to original sources

bioRxiv2026

The structure of a 2-MDa chloroplast RNA polymerase reveals unexpected evolutionary complexity

Transcription in chloroplasts depends on the Plastid-Encoded RNA polymerase (PEP), a bacterial-derived enzyme whose catalytic core remains encoded by the highly reduced genome inherited from the cyanobacterial ancestor. In land plants, PEP has roughly doubled in size, expanding into a [~]1 MDa multisubunit machinery through the acquisition of numerous nuclear-encoded subunits. Based on phylogenetic analyses, this added complexity has been widely attributed to the demands of plant terrestrialization. Contrary to this view, we show that in the unicellular green alga Chlamydomonas reinhardtii, PEP assembles into an even larger [~]2 MDa complex containing twelve previously uncharacterized nuclear-encoded subunits (PEPS1-12), representing an RNA polymerase architecture of unprecedented size. A cryo-EM structure at 2.7 [A] resolution reveals that several of these subunits occupy positions analogous to those in land plant PEP, and that metabolic enzyme folds have been repurposed as structural scaffolds stabilizing the highly expanded plastid-encoded core. Despite this, most of the newly identified PEPS subunits lack detectable sequence or structural similarity to their land plant counterparts. These findings demonstrate that PEP complexity is not a hallmark of land plant evolution and may instead reflect, at least in part, the evolutionary entrenchment of additional subunits around an expanded plastid-encoded core. More broadly, they suggest that essential organellar machines can acquire substantial structural complexity that leaves little trace in sequence-based analyses, a pattern consistent with constructive neutral evolution.

molecular biology↗

bioRxiv2026

Septin-mediated coupling of protein import and division during chloroplast evolution

Chloroplast biogenesis depends on both protein import and organelle division, yet how their coordination emerged during evolution remains unclear. Here, we show that the single septin SEP1 links these pathways in the green alga Chlamydomonas reinhardtii. SEP1 forms a filamentous network on the chloroplast envelope during interphase and reorganizes into a ring at the chloroplast division site during cytokinesis. Loss of SEP1 selectively impairs import of chloroplast-division proteins and causes mispositioning of the division ring, without impairing bulk chloroplast protein import. SEP1 physically associates with outer-envelope TOC GTPases through evolutionarily related GTPase domains. Phylogenetic analysis places TOC GTPases within an algal septin-derived clade, and heterologous expression of SEP1 in land plants, in which septins are absent, shows conservation of its chloroplast targeting and TOC binding. Together, these findings identify septins as coordinators of plastid protein import and division and suggest that this coupling emerged early in chloroplast evolution.

cell biology↗

bioRxiv2026

VIA1 is a conserved regulator of thylakoid membrane integrity that acts through VIPP1

Thylakoid membranes are indispensable for oxygenic photosynthesis, yet the mechanisms that protect these membranes from photooxidative damage remain poorly understood. By screening previously uncharacterized proteins induced during the chloroplast unfolded protein response, we identify VIA1 as an essential factor for preserving thylakoid integrity under high light in the model green alga Chlamydomonas reinhardtii. Loss of VIA1 causes hypersensitivity to photo-oxidative stress and rapid thylakoid swelling. VIA1 localizes to thylakoid membranes and directly binds Vesicle-Inducing Protein in Plastids 1 (VIPP1), an ESCRT-III-like protein essential for thylakoid biogenesis and remodeling. Structure-guided mutagenesis shows that this interaction is required for VIA1 function and is mediated by a winged-helix domain interface reminiscent of ESCRT-II/ESCRT-III binding mode. VIA1 orthologs from cyanobacteria and land plants rescue the Chlamydomonas via1 mutant phenotype, and disruption of VIA1 in Synechocystis sp. PCC 6803 impairs growth, especially under light stress. Together, these findings establish VIA1 as an evolutionarily conserved protein that contributes to thylakoid membrane homeostasis via its interaction with VIPP1. Significance StatementFrom cyanobacteria to land plants, all organisms performing oxygenic photosynthesis rely on thylakoid membranes to capture light and and produce oxygen. Yet these membranes are highly susceptible to environmental stress, particularly excess light, which causes oxidative damage to membrane lipids and proteins. How thylakoid integrity is maintained under these conditions remains a key open question. Here we identify VIA1 as a conserved factor required for maintaining thylakoid membrane structure under high light. VIA1 interacts with VIPP1, an ESCRT-III-like protein essential for thylakoid biogenesis, through a functionally indispensable interface reminiscent of ESCRT-II/ESCRT-III binding mode. The conservation of the VIA1-VIPP1 module across photosynthetic prokaryotes and eukaryotes suggests it arose early in the evolution of oxygenic photosynthesis and has been maintained ever since.

cell biology↗

bioRxiv2023

A conserved ESCRT-II-like protein participates in the biogenesis and maintenance of thylakoid membranes

Thylakoids are membrane-bound compartments located in cyanobacteria and chloroplasts of plants and algae. They play an indispensable role in the light-driven reactions that enable photosynthetic organisms to convert water and carbon dioxide into oxygen and sugars. The biogenesis and maintenance of thylakoid membranes is a critical yet underappreciated area of research. One of the few known critical regulators of this process, VIPP1 (Vesicle-Inducing Protein in Plastids 1), was recently shown to be structurally similar to ESCRT-III proteins -- the first evidence for ESCRT-like (Endosomal Sorting Complex Required for Transport) machinery in chloroplasts. Here, we used an affinity purification approach in two distantly related photosynthetic eukaryotes, the green alga Chlamydomonas reinhardtii and the plant Arabidopsis thaliana, to discover proteins that interact with VIPP1. Among several newly identified proteins, we focused on a highly conserved but uncharacterized protein (VIPP1-Associated protein 1, VIA1) that robustly interacts with VIPP1 in both systems. VIA1 is predicted to contain a winged-helix domain, a characteristic feature of ESCRT-II proteins that mediates the interaction with ESCRT-III proteins. The absence of VIA1 causes thylakoid swelling upon exposure to high light in Chlamydomonas and defective thylakoid biogenesis in the newly emerging leaf tissue in Arabidopsis, thereby delaying chloroplast development in this tissue. We propose that VIA1 is part of a previously unrecognized chloroplast ESCRT-like system that plays a critical role in forming, remodeling, and repairing photosynthetic membranes. Significance StatementThylakoid membranes are essential for photosynthesis, yet their biogenesis and maintenance are poorly understood. Of the few known proteins involved in these processes, VIPP1 stands out due to its similarity to ESCRT-III, an integral component of the ESCRT machinery that is responsible for membrane remodeling and trafficking in the cytoplasm of eukaryotes. Here we report the discovery of VIA1, a conserved protein that interacts with VIPP1 and participates in thylakoid biogenesis and remodeling in two distantly related photosynthetic organisms. Because VIA1 contains a predicted winged-helix domain, a hallmark feature of ESCRT-II proteins that mediates the interaction with ESCRT-III proteins, our data support the hypothesis that universal, mechanistic principles govern membrane remodeling across all living organisms.

plant biology↗