Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
Plant J. 2011 Mar;65(6):949-57. doi: 10.1111/j.1365-313X.2011.04480.x. Epub 2011 Feb 18.
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.
植物对创伤的反应是其防御昆虫侵害的一部分，并且受到严格的调控。茉莉酸的异亮氨酸轭合物（JA-Ile）是主要的调节分子。我们之前已经表明，肌醇多磷酸信号对于拟南芥的防御反应是必需的；然而，肌醇多磷酸如何促进植物对创伤的反应目前仍不清楚。参与 JA-Ile（COI1）和生长素（TIR1）感知的拟南芥 F-box 蛋白在结构上相似。因为 TIR1 最近被证明含有肌醇六磷酸（InsP₆）作为未知功能的辅助因子，所以在这里我们探讨了 InsP₆或另一种肌醇多磷酸是否是 COI1 功能所必需的。支持这一假设，在酵母双杂交试验中，具有假定肌醇多磷酸配位残基变化的 COI1 变体与 COI1 靶标 JAZ9 的相互作用减弱。在 coi1 突变体中，具有相同 COI1 变体的拟南芥显示出降低了恢复茉莉酸介导的根生长抑制或蒴果发育的能力。使用野生型 COI1 在 ipk1Δ 酵母菌株中进行的酵母双杂交试验表明，肌醇五磷酸（InsP₅）水平增加，InsP₆水平降低，表明 COI1/JAZ9 相互作用增强。与这些发现一致的是，肌醇多磷酸代谢改变的 Arabidopsis ipk1-1 突变体也表现出增加的防御能力，包括通过 COI1 介导的过程，包括创伤诱导的基因表达、对毛毛虫的防御或茉莉酸引起的根生长抑制。使用突变 COI1 变体以及肌醇多磷酸代谢改变的酵母和拟南芥背景进行的实验的综合数据表明，肌醇多磷酸，可能是 InsP₅，有助于 COI1 功能。
