Plant cells are well equipped to sense and integrate endogenous and environmental signals. Signal perception is one of the most basic processes that enables plants to develop into mature, fertile organisms. One of the most surprising recent discoveries in plant science was that the SR160 cell surface receptor for the wound signaling peptide systemin is identical to the tBRI1 receptor for brassinosteroids, steroidal plant hormones that regulate growth and development. Furthermore, the systemin receptor might be co-opted by ultraviolet-B radiation. While systemin and brassinosteroids are ligands for the same receptor, their signal transduction and target genes are known to be different. On the other hand, UV-B- and systemin-induced signaling and gene expression overlap. This project is concerned with the regulation of the membrane-spanning SR160/tBRI1 receptor by systemin, brassinosteroids, and UV-B at the biochemical and molecular level. It is hypothesized that either the mode of activation of SR160/tBRI1 or the recruitment of other intracellular signaling proteins to SR160/tBRI1 differs in a ligand-dependent manner. Using tomato and tobacco as model plants, the focus will be on the activation by phosphorylation of the intracellular domain of the receptor, and on the identification and characterization of interacting proteins. In addition, it will be tested whether UV-B activates SR160/tBRI1 and recruits the same proteins to the receptor as systemin. The hypotheses will be tested experimentally by employing phosphorylation assays, the yeast two-hybrid system to identify SR160/tBRI1 interacting proteins, and a protoplast transient transformation system for in vivo studies. The project should lead to fundamental insights into stress perception that will be useful for devising strategies for generating plants with increased resistance to various stress factors. These plants would reduce the application of environmentally harmful agrochemicals such as pesticides and increase the yield of crop plants under unfavorable environmental conditions. The project will involve a postdoctoral research associate and undergraduate students who will be trained in state-of-the-art methods in plant molecular biology. Research related to this project will be incorporated in an upper level class for undergraduate and graduate students, taught by the PI. Underrepresented groups will be actively recruited to participate in the project.
