Jasmonic acid perception by COI1 involves inositol polyphosphates in Arabidopsis thaliana
Plant responses to wounding are part of their defense responses against insects, and are tightly regulated. The isoleucin conjugate of jasmonic acid (JA-Ile) is a major regulatory molecule. We have previously shown that inositol polyphosphate signals are required for defense responses in Arabidopsis; however, the way in which inositol polyphosphates contribute to plant responses to wounding has so far remained unclear. Arabidopsis F-box proteins involved in the perception of JA-Ile (COI1) and auxin (TIR1) are structurally similar. Because TIR1 has recently been shown to contain inositol hexakisphosphate (InsP6) as a co-factor of unknown function, here we explored the possibility that InsP6 or another inositol polyphosphate is required for COI1 function. In support of this hypothesis, COI1 variants with changes in putative inositol polyphosphate coordinating residues exhibited a reduced interaction with the COI1 target, JAZ9, in yeast two-hybrid tests. The equivalent COI1 variants displayed a reduced capability to rescue jasmonate-mediated root growth inhibition or silique development in Arabidopsis coi1 mutants. Yeast two-hybrid tests using wild-type COI1 in an ipk1Δ yeast strain exhibiting increased levels of inositol pentakisphosphate (InsP5) and reduced levels of InsP6 indicate an enhanced COI1/JAZ9 interaction. Consistent with these findings, Arabidopsis ipk1-1 mutants, also with increased InsP5 and reduced InsP6 levels, showed increased defensive capabilities via COI1-mediated processes, including wound-induced gene expression, defense against caterpillars or root growth inhibition by jasmonate. The combined data from experiments using mutated COI1 variants, as well as yeast and Arabidopsis backgrounds altered in inositol polyphosphate metabolism, indicate that an inositol polyphosphate, and probably InsP5, contributes to COI1 function.
Document Type: Research Article
Affiliations: 1: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany 2: Department of Molecular Biology and Physiology, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, Untere Karspüle 2, 37073 Göttingen, Germany
Publication date: March 1, 2011