Biology subjects

Timmermans, M. C. P.

Publications and source records attributed to Timmermans, M. C. P..

3 recordsLinked to original sources

bioRxiv2022

The START domain potentiates HD-ZIPIII transcriptional activity

HD-ZIPIII transcription factors (TFs) were repeatedly deployed over 725 million years of evolution to regulate central developmental innovations. The START domain of this pivotal class of developmental regulators was recognized over twenty years ago, but its putative ligands and functional contributions remain unknown. Here, we demonstrate that the START domain promotes HD-ZIPIII TF homodimerization and increases transcriptional potency. Effects on transcriptional output can be ported onto heterologous TFs, consistent with principles of evolution via domain capture. We also show the START domain binds several species of phospholipids, and that mutations in conserved residues predicted to affect either ligand binding, or its downstream readout, abolish HD-ZIPIII DNA-binding competence. Our data present a model in which the START domain potentiates transcriptional activity and uses ligand-induced conformational change to render HD-ZIPIII dimers competent to bind DNA. These findings resolve a long-standing mystery in plant development and highlight the flexible and diverse regulatory potential coded within this widely distributed evolutionary module.

plant biology↗

bioRxiv2020

Unique and distinct identities and functions of leaf phloem cells revealed by single cell transcriptomics

AO_SCPLOWBSTRACTC_SCPLOWThe leaf vasculature plays a key role in solute translocation. Veins consist of at least seven distinct cell types, with specific roles in transport, metabolism, and signaling. Little is known about the vascular cells in leaves, in particular the phloem parenchyma (PP). PP effluxes sucrose into the apoplasm as a basis for phloem loading; yet PP has only been characterized microscopically. Here, we enriched vascular cells from Arabidopsis leaves to generate a single-cell transcriptome atlas of leaf vasculature. We identified [≥]19 cell clusters, encompassing epidermis, guard cells, hydathodes, mesophyll, and all vascular cell types, and used metabolic pathway analysis to define their roles. Clusters comprising PP cells were enriched for transporters, including SWEET11 and SWEET12 sucrose and UmamiT amino acid efflux carriers. PP development occurs independently from APL, a transcription factor required for phloem differentiation. PP cells have a unique pattern of amino acid metabolism activity distinct from companion cells (CC), explaining differential distribution/metabolism of amino acids in veins. The kinship relation of the vascular clusters is strikingly similar to the vein morphology, except for a clear separation of CC from the other vascular cells including PP. In summary, our scRNA-seq analysis provides a wide range of information into the leaf vasculature and the role and relationship of the leaf cell types.

plant biology↗

bioRxiv2020

Noxious effects of cell surface display glutamate sensors on plant growth and development

Plants use electrical and chemical signals for systemic communication. Herbivory, for instance, appears to trigger local apoplasmic glutamate accumulation, systemic electrical signals and calcium waves that travel to report insect damage to neighboring leaves and initiate defense. To monitor extra- and intracellular glutamate concentrations in plants, we generated Arabidopsis lines expressing genetically encoded fluorescent glutamate sensors. In contrast to cytosolically localized sensors, extracellularly displayed variants inhibited plant growth and proper development. Phenotypic analyses of high-affinity display sensor lines revealed that root meristem development, particularly the quiescent center (QC), number of lateral roots, vegetative growth and floral architecture were impacted. Notably, the severity of the phenotypes was positively correlated with the affinity of the display sensors, intimating that their ability to sequester glutamate at the surface of the plasma membrane was responsible for the defects. Root growth defects were suppressed by supplementing culture media with low levels of glutamate. Together, the data indicate that sequestration of glutamate at the cell surface either disrupts the supply of glutamate to meristematic cells and/or impairs localized glutamatergic signaling important for developmental processes. SIGNIFICANCE STATEMENTGlutamate is an important signaling molecule in animals and plants. The affinity-dependent effects of surface-displayed glutamate sensors on plant development intimate that glutamate levels in the vicinity of the plasma membrane play important roles in signaling in plants.

plant biology↗