Mass spectrometric based analysis of receptor mediated hormone signaling in Arabidopsis

In the work described herein, I chose to study the two plant hormones ABA and RALF using a quantitative phosphoproteomics workflow that I helped establish. The ABA work (Chapter 2) consists of an in depth phosphoproteomic approach to address the hypothesized redundant nature of the ABA receptors, followed by validation of a set of results using targeted mass spectrometry. The FERONIA work (Chapter 3) describes biochemical experiments designed to hone in on a single significant result from an analogous large-scale phosphoproteomic study. I have endeavored to approach plant hormone signaling from two different angles, ultimately hoping to gain insight into both the biology and biochemistry driving such processes. The ABA work described herein has provided a view of ABA signaling that would be hard to obtain without the mass spectrometers and techniques unique to the Sussman laboratory, and the FERONIA work described couldn't have been done without the uniquely friendly and collaborative environment at UW-Madison. Chapter 2 demonstrates that the initial events directing ABA signal transduction may be more complicated than once thought, and Chapter 3 begins biochemical characterization of the RALF peptide hormone receptor, FERONIA, one of the hundreds of so-called plant "orphan RLKs," an enigmatic and complex family of proteins unique to plants. Ultimately, the work done in both chapters describes what can be done following large-scale phosphoproteomic experiments. I hope that many studies like those described herein will follow the publication of this thesis; the techniques and workflows are universal and can be applied to any plant hormone for which the receptors are unknown or more detailed information about its signaling cascades is desired.