Function Tetraspanins and Tetraspanin-like Proteins in Plant Signaling

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This project is aimed at understanding how signaling molecules that coexist at the cell surface find each other to mediate cellular responses. Key proteins at the cell surface need to be able to transiently interact with each other when they encounter specific stimuli to trigger a response within the cell. How do the signaling partners find each other in a sea of membrane lipids? A mechanism that cells use to confine membrane proteins to specific domains in a continuous membrane is the expression of proteins that are able to establish protein networks or webs. Tetraspanins are evolutionarily-conserved proteins that facilitate the formation of protein networks and establish signaling modules involved in intercellular communication, cell proliferation, development, and specific responses to biotic and abiotic stimuli. However, there is very little experimental data on their exact molecular mechanisms and what physiological roles they play in plants. This project will analyze the function of tetraspanin and tetraspanin-like proteins in the model plant Arabidopsis thaliana to understand their molecular and physiological roles in vascular development, cell proliferation, and responses to phytohormones. The researcher and her group have identified a plant-specific protein family that shares key structural and functional similarities with tetraspanins. In Arabidopsis thaliana, one member of this family named VASCULAR COMPLEXITY AND CONECTIVITY (VCC) controls vascular development. VCC interacts with TETRASPANIN 1 (TET1) and other signaling molecules involved in vasculature development and localizes to the plasma membrane. The researcher proposes that tetraspanins, VCC proteins, and likely other membrane associated proteins act in a combinatorial manner to establish protein-network modules that contain different associations of receptors and signaling components specific to different plant cell types/tissues. In this context, the evolution of plant tetraspanin-like proteins like the VCC family could have potentially increased the diversity and specificity of protein signaling modules on membranes. This project will analyze two plant tetraspanin signaling modules involved in very different processes. One module is at the plasma membrane, consists of TET1, VCC, and the membrane-associated protein OCTOPUS (OPS), and positively regulates vascular differentiation in Arabidopsis embryos. The other module localizes to the endoplasmic reticulum, contains TET6, and controls seed longevity, seed responses to abscisic acid and oxidative stress during germination. The goals are to identify what other structuring components (other tetraspanins, VCC, or other TET-like proteins) and signaling molecules (e.g. receptors) are part of these signaling modules, to determine what signaling/physiological events they control, and to explore the function and composition of other tetraspanins and VCC protein networks in Arabidopsis though genetic, proteomic, and molecular approaches. This project will provide interdisciplinary training to a postdoctoral fellow, a graduate student, and several undergraduate researchers enrolled in UW-Madison or attending its summer REU program through the Integrated Biological Sciences Summer Research Program. The proposed research will also impact classroom education at the University of Wisconsin. The Principal Investigator teaches three hands-on undergraduate and graduate courses that require the completion of a research project in plant biology. In addition, thirty students taking the Introduction to Engineering Design course at the UW-Madison campus, will interact with the research team on this poroject and design a device specially optimized to facilitate the imaging of plant membrane proteins in intact Arabidopsis embryos and seedlings under controlled environmental conditions.