The balance of inositol polyphosphates as a regulator of auxin and jasmonate perception in Arabidopsis thaliana

Arabidopsis plants perceive the phytohormones auxin and jasmonate (JA) through specific receptor proteins (Transport Inhibitor Response 1, TIR1, and Coronatine Insensitive 1, COI1, respectively), which are F-box-proteins and serve as components of ubiquitin-ligase complexes. The presence of the phytohormones leads to ubiquitinylation and proteasomal degradation of specific transcriptional repressors, thereby enabling auxin-dependent or JA-dependent gene expression. For TIR1 and auxin perception these repressors are AUX/IAA-proteins; for COI1 and JA-perception the corresponding repressors are the JAZ-proteins. A possible link of auxin- or JA-perception to signaling via inositol polyphosphates (IPPs) is presented by the notion that both TIR1 and COI1 contain IPPs as cofactors (TIR1: inositolhexakisphosphate, IP6; COI1: inositolpentakisphosphate, IP5) and we postulate that the IPPs in TIR1 and COI1 control receptor function. Because IP6 and IP5 can be interconverted by single-step enzymatic reactions, it appears plausible that the balance of these IPP-cofactors is crucial for the orchestration of auxin-dependent vs. JA-dependent processes in plants. The proposed experiments are designed to first characterize the so-far-unknown dynamics of IP5 and IP6 upon gravistimulation and wounding. Data acquired in the planned project will elucidate the still-enigmatic roles of IPPs in plants and contribute to the understanding how the outputs of different signaling pathways are integrated.