Exploring new links between phosphoinositides and phytohormone signaling in Arabidopsis thaliana

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The integration of phosphoinositides (PIs) with plant phytohormones is illdefined. Changes in PIs and PI-derived inositolpolyphosphates (IPs) coincide with changes in auxin (IAA) or jasmonate (JA) during responses to gravistimulation and wounding, suggesting that PIs act in both IAA- and JA-signaling cascades. The recent discovery of an inositolhexakisphosphate (InsP6) cofactor of the auxin receptor, TIR1, suggests a role for IPs in the function of TIR1 or the related JA-receptor protein, COI1. It is the goal of the proposed work to elucidate how PIderived signaling molecules contribute to phytohormone receptor function. Arabidopsis wild type-plants and transgenic lines compromised in different aspects of PI-signaling will be stimulated by A) gravitropism and B) mechanical wounding, and physiological responses will be recorded. Stress-induced transcript changes will be investigated by a microarray approach to delineate PIs with signaling functions dependent or independent of TIR1 or COI1. Changes in the patterns of PIs, IAA, JA or other phytohormones will be systematically analyzed biochemically and using fluorescent reporters. TIR1 and COI1 interactions with their respective transcriptional repressors, Aux/IAA or JAZ, will be tested in vivo in the presence or absence of InsP6. Residues coordinating InsP6 in TIR1 and COI1 will be changed based on the TIR1 crystal structure and the engineered proteins tested for functionality in mutant complementation assays. The involvement of PIs in IAA- or JA-signaling will be cross-tested for relevance during plant development.