Diversity of retromer-mediated vesicular trafficking pathways in plants

The plant endomembrane system is organized and regulated by large gene families that encode proteins responsible for the spatiotemporal delivery and retrieval of cargo throughout the cell and to and from the plasma membrane. Many of these regulatory molecules form functional complexes like the SNAREs, exocyst, and retromer, which are required for the delivery, recycling, and degradation pathways of cellular components. The functions of these complexes are well conserved in eukaryotes, but the extreme expansion of the protein subunit families in plants suggests that plant cells require more regulatory specialization when compared with other eukaryotes. The retromer is associated with retrograde sorting and trafficking of protein cargo back towards the TGN and vacuole in plants, while in animals, there is new evidence that the VPS26C ortholog is associated with recycling or 'retrieving' proteins back to the PM from the endosomes. The human VPS26C was shown to rescue vps26c mutant phenotypes in Arabidopsis thaliana, suggesting that the retriever function could be conserved in plants. This switch from retromer to retriever function may be associated with core complexes that include the VPS26C subunit in plants, similar to what has been suggested in other eukaryotic systems. We review what is known about retromer function in light of recent findings on functional diversity and specialization of the retromer complex in plants.

Vision, challenges and opportunities for a Plant Cell Atlas

With growing populations and pressing environmental problems, future economies will be increasingly plant-based. Now is the time to reimagine plant science as a critical component of fundamental science, agriculture, environmental stewardship, energy, technology and healthcare. This effort requires a conceptual and technological framework to identify and map all cell types, and to comprehensively annotate the localization and organization of molecules at cellular and tissue levels. This framework, called the Plant Cell Atlas (PCA), will be critical for understanding and engineering plant development, physiology and environmental responses. A workshop was convened to discuss the purpose and utility of such an initiative, resulting in a roadmap that acknowledges the current knowledge gaps and technical challenges, and underscores how the PCA initiative can help to overcome them.

First plant cell atlas workshop report

The societal challenges posed by a growing human population and climate change necessitate technical advances in plant science. Plant research makes vital contributions to society by advancing technologies that improve agricultural food production, biological energy capture and conversion, and human health. However, the plant biology community lacks a comprehensive understanding of molecular machinery, including their locations within cells, distributions and variations among different cell types, and real-time dynamics. Fortunately, rapid advances in molecular methods, imaging, proteomics, and metabolomics made in the last decade afford unprecedented opportunities to develop a molecular-level map of plant cells with high temporal and spatial resolution. The Plant Cell Atlas (PCA) initiative aims to generate a resource that will provide fresh insight into poorly understood aspects of plant cell structure and organization and enable the discovery of new cellular compartments and features. The PCA will be a community resource (www.plantcellatlas.org/) that describes the state of various plant cell types and integrates high-resolution spatio-temporal information of nucleic acids, proteins, and metabolites within plant cells. This first PCA initiative workshop convened scientists passionate about developing a comprehensive PCA to brainstorm about the state of the field, recent advances, the development of tools, and the future directions of this initiative. The workshop featured invited talks to share initial data, along with broader ideas for the PCA. Additionally, breakout sessions were organized around topics including the conceptual goals of the PCA, technical challenges, and community wants and needs. These activities connected scientists with diverse expertise and sparked important discussions about how to leverage and extend leading-edge technologies and develop new techniques. A major outcome of the workshop was that the community wishes to redefine concepts of plant cell types and tissues quantitatively. A long-term goal is to delineate all molecules within the cell at high spatio-temporal resolution, obtain information about interacting molecular networks, and identify the contribution of these networks to development of the organism as a whole. As a first step, we wish to create comprehensive cellular and subcellular biomolecular maps of transcripts, proteins, and metabolites, track the dynamic interactions of these molecules intra- and intercellularly, discern complete states and transitions of specialized cell types, and integrate these disparate data points to generate testable models of cellular function. Ultimately, the PCA initiative will have a substantial positive impact by empowering a broad, diverse group of scientists to forge exciting paths in the field of plant science, facilitating connections with interested stakeholders beyond the scientific community, and enabling new agricultural technologies for a sustainable future.

Vacuolar Protein Sorting 26C encodes an evolutionarily conserved large retromer subunit in eukaryotes that is important for root hair growth in Arabidopsis thaliana

The large retromer complex participates in diverse endosomal trafficking pathways and is essential for plant developmental programs, including cell polarity, programmed cell death and shoot gravitropism in Arabidopsis. Here we demonstrate that an evolutionarily conserved VPS26 protein (VPS26C; At1G48550) functions in a complex with VPS35A and VPS29 necessary for root hair growth in Arabidopsis. Bimolecular fluorescence complementation showed that VPS26C forms a complex with VPS35A in the presence of VPS29, and this is supported by genetic studies showing that vps29 and vps35a mutants exhibit altered root hair growth. Genetic analysis also demonstrated an interaction between a VPS26C trafficking pathway and one involving the SNARE VTI13. Phylogenetic analysis indicates that VPS26C, with the notable exception of grasses, has been maintained in the genomes of most major plant clades since its evolution at the base of eukaryotes. To test the model that VPS26C orthologs in animal and plant species share a conserved function, we generated transgenic lines expressing GFP fused with the VPS26C human ortholog (HsDSCR3) in a vps26c background. These studies illustrate that GFP-HsDSCR3 is able to complement the vps26c root hair phenotype in Arabidopsis, indicating a deep conservation of cellular function for this large retromer subunit across plant and animal kingdoms.