Small molecule RHP1 promotes root hair tip growth by acting upstream of the RHD6-RSL4-dependent transcriptional pathway and ROP signaling in plants.

Root hairs are single-cell projections in the root epidermis. The presence of root hairs greatly expands the root surface, which facilitates soil anchorage and the absorption of water and nutrients. Root hairs are also the ideal system to study the mechanism of polar growth.

A small molecule antagonizes jasmonic acid perception and auxin responses in vascular and nonvascular plants.

The phytohormone jasmonoyl-L-isoleucine (JA-Ile) regulates many stress responses and developmental processes in plants. A co-receptor complex formed by the F-box protein Coronatine Insensitive 1 (COI1) and a Jasmonate (JA) ZIM-domain (JAZ) repressor perceives the hormone. JA-Ile antagonists are invaluable tools for exploring the role of JA-Ile in specific tissues and developmental stages, and for identifying regulatory processes of the signaling pathway.

Interaction between VPS35 and RABG3f is necessary as a checkpoint to control fusion of late compartments with the vacuole.

Vacuoles are essential organelles in plants, playing crucial roles, such as cellular material degradation, ion and metabolite storage, and turgor maintenance. Vacuoles receive material via the endocytic, secretory, and autophagic pathways. Membrane fusion is the last step during which prevacuolar compartments (PVCs) and autophagosomes fuse with the vacuole membrane (tonoplast) to deliver cargoes.

Drug Affinity Responsive Target Stability (DARTS) to Resolve Protein-Small Molecule Interaction in Arabidopsis.

Target identification remains a challenging step in plant chemical genomics approaches. Drug affinity responsive target stability (DARTS) represents a straightforward technique to identify small molecules' protein targets and assist in the characterization of interactions between small molecules and putative targets identified by other methods. When a small molecule interacts with a protein, it has the potential to stabilize the protein's structure, resulting in a reduced susceptibility to protease action.

Merging roads: chemical tools and cell biology to study unconventional protein secretion.

The endomembrane trafficking network is highly complex and dynamic, with both conventional and so-called unconventional routes which are in essence recently discovered pathways that are poorly understood in plants. One approach to dissecting endomembrane pathways that we have pioneered is the use of chemical biology. Classical genetic manipulations often deal with indirect pleiotropic phenotypes resulting from the perturbation of key players of the trafficking routes.

Pyrazinamide and derivatives block ethylene biosynthesis by inhibiting ACC oxidase.

Ethylene is an important phytohormone that promotes the ripening of fruits and senescence of flowers thereby reducing their shelf lives. Specific ethylene biosynthesis inhibitors would help to decrease postharvest loss. Here, we identify pyrazinamide (PZA), a clinical drug used to treat tuberculosis, as an inhibitor of ethylene biosynthesis in Arabidopsis thaliana, using a chemical genetics approach.

Different Endomembrane Trafficking Pathways Establish Apical and Basal Polarities.

The endomembrane system is an interconnected network required to establish signal transduction, cell polarity, and cell shape in response to developmental or environmental stimuli. In the model plant , there are numerous markers to visualize polarly localized plasma membrane proteins utilizing endomembrane trafficking. Previous studies have shown that the large ARF-GEF GNOM plays a key role in the establishment of basal (rootward) polarity, whereas the apically (shootward) polarized membrane proteins undergo sorting via different routes.

Firmly Planted, Always Moving.

I was a budding pianist immersed in music in Leningrad, in the Soviet Union (now Saint Petersburg, Russia), when I started over, giving up sheet music for the study of ciliates. In a second starting-over story, I emigrated to the United States, where I switched to studying carbohydrate-binding plant lectin proteins, dissecting plant vesicular trafficking, and isolating novel glycosyltransferases responsible for making cell wall polysaccharides. I track my journey as a plant biologist from student to principal investigator to founding director of the Center for Plant Cell Biology and then director of the Institute for Integrative Genome Biology at the University of California, Riverside.

Enrichment of hydroxylated C24- and C26-acyl-chain sphingolipids mediates PIN2 apical sorting at trans-Golgi network subdomains.

The post-Golgi compartment trans-Golgi Network (TGN) is a central hub divided into multiple subdomains hosting distinct trafficking pathways, including polar delivery to apical membrane. Lipids such as sphingolipids and sterols have been implicated in polar trafficking from the TGN but the underlying mechanisms linking lipid composition to functional polar sorting at TGN subdomains remain unknown. Here we demonstrate that sphingolipids with α-hydroxylated acyl-chains of at least 24 carbon atoms are enriched in secretory vesicle subdomains of the TGN and are critical for de novo polar secretory sorting of the auxin carrier PIN2 to apical membrane of Arabidopsis root epithelial cells.

Endosidin2 targets conserved exocyst complex subunit EXO70 to inhibit exocytosis.

The exocyst complex regulates the last steps of exocytosis, which is essential to organisms across kingdoms. In humans, its dysfunction is correlated with several significant diseases, such as diabetes and cancer progression. Investigation of the dynamic regulation of the evolutionarily conserved exocyst-related processes using mutants in genetically tractable organisms such as Arabidopsis thaliana is limited by the lethality or the severity of phenotypes.

Sortin2 enhances endocytic trafficking towards the vacuole in Saccharomyces cerevisiae.

Background: A highly regulated trafficking of cargo vesicles in eukaryotes performs protein delivery to a variety of cellular compartments of endomembrane system. The two main routes, the secretory and the endocytic pathways have pivotal functions in uni- and multi-cellular organisms. Protein delivery and targeting includes cargo recognition, vesicle formation and fusion.

An early secretory pathway mediated by GNOM-LIKE 1 and GNOM is essential for basal polarity establishment in Arabidopsis thaliana.

Spatial regulation of the plant hormone indole-3-acetic acid (IAA, or auxin) is essential for plant development. Auxin gradient establishment is mediated by polarly localized auxin transporters, including PIN-FORMED (PIN) proteins. Their localization and abundance at the plasma membrane are tightly regulated by endomembrane machinery, especially the endocytic and recycling pathways mediated by the ADP ribosylation factor guanine nucleotide exchange factor (ARF-GEF) GNOM.

Molecular Composition of Plant Vacuoles: Important but Less Understood Regulations and Roles of Tonoplast Lipids.

The vacuole is an essential organelle for plant growth and development. It is the location for the storage of nutrients; such as sugars and proteins; and other metabolic products. Understanding the mechanisms of vacuolar trafficking and molecule transport across the vacuolar membrane is of great importance in understanding basic plant development and cell biology and for crop quality improvement.

Arabidopsis ribosomal proteins control vacuole trafficking and developmental programs through the regulation of lipid metabolism.

The vacuole is the most prominent compartment in plant cells and is important for ion and protein storage. In our effort to search for key regulators in the plant vacuole sorting pathway, ribosomal large subunit 4 (rpl4d) was identified as a translational mutant defective in both vacuole trafficking and normal development. Polysome profiling of the rpl4d mutant showed reduction in polysome-bound mRNA compared with wild-type, but no significant change in the general mRNA distribution pattern.

Plant vacuole morphology and vacuolar trafficking.

Plant vacuoles are essential organelles for plant growth and development, and have multiple functions. Vacuoles are highly dynamic and pleiomorphic, and their size varies depending on the cell type and growth conditions. Vacuoles compartmentalize different cellular components such as proteins, sugars, ions and other secondary metabolites and play critical roles in plants response to different biotic/abiotic signaling pathways.

Plant chemical biology: are we meeting the promise?

As an early adopter of plant chemical genetics to the study of endomembrane trafficking, we have observed the growth of small molecule approaches. Within the field, we often describe the strengths of the approach in a broad, generic manner, such as the ability to address redundancy and lethality. But, we are now in a much better position to evaluate the demonstrated value of the approach based on examples.

1H NMR-based metabolomics methods for chemical genomics experiments.

Metabolomics and chemical genomics studies can each provide unique insights into plant biology. Although a variety of analytical techniques can be used for the interrogation of plant systems, nuclear magnetic resonance (NMR) provides unbiased characterization of abundant metabolites. An example methodology is provided for probing the metabolism of Arabidopsis thaliana in a chemical genomics experiment including methods for tissue treatment, tissue collection, metabolite extraction, and methods to minimize variance in biological and technical sample replicates.

High-throughput identification of chemical endomembrane cycling disruptors utilizing tobacco pollen.

Endomembrane cycling processes in plants remain mostly intractable through classical genetic interrogation. Chemical disruption of these processes provides an opportunity to slow or inhibit these processes for study. Tobacco pollen, which is dependent upon endomembrane cycling for tube growth, provides a plant system that is amenable to high-throughput screening of chemical disruptors.