茉莉酸与赤霉素互作调控接触性形态建成的分子机理研究

Plants evolved very sensitive mechanisms to respond to even very subtle stimuli, such as touching. For example, Arabidopsis plants whose rosette leaves are gently moved back and forth repeatedly over the course of their development exhibit delayed transition to flowering, decreased flowering stem (inflorescence) elongation, and shorter petioles that contribute to the development of smaller rosettes. Touch-induced developmental alterations, called thigmomorphogenesis, are thought to be conserved among most plants. The phytohormone jasmonic acid (JA) is important for thigmomorphogenesis: JA levels increase in response to touching; the JA-biosynthesis mutant aos and the coi1 mutant, which is defect in JA perception, are not sensitive to touching. However, the mechanism by which touching-induced JA inhibits plant development remains unclear. Our preliminary work shows: 1. the q-della mutant, in which four of five Arabidopsis gibberellin (GA)-signaling repressors lose functions, is insensitive to touching; 2. the transcripts of some GA biosynthesis enzymes are down-regulated after touching in wild-type Arabidopsis, but they are not changed in aos and coi1 mutants. Based on these observations, we hypothesize that touching-induced JA antagonizes the biosynthesis of GAs, the phytohormone regulates major aspects of plant growth and development, and thus touched plants shows growth inhibition. To test this, we will compare the GA levels in JA-deficient mutants and wild-type Arabidopsis. Moreover, we will also test whether exogenous GA treatment can restore touching-induced growth retardation. To gain further insight into the mechanism by which touching-induced JA inhibits the expression of GA biosynthesis genes, DNA-protein interaction assays will be employed to examine whether the transcript factor MYC2, the master regulator of JA responses, binds to the promoter regions of important GA biosynthesis genes and thus repress their expression. This study will expand our knowledge on the mechanism underlying JA-GA crosstalk in regulating thigmomorphogensis.

植物演化出了非常敏感的机制可以对极微弱的刺激做出反应，如每天触摸拟南芥叶片会抑制其生长。这种因接触性刺激而产生的形态变化被称作接触性形态建成（thigmomorphogenesis）。茉莉酸对接触性形态建成非常重要：触摸后植物中的茉莉酸升高，且茉莉酸合成及感受突变体对触摸不敏感。但是触摸诱导的茉莉酸抑制植物生长的分子机理还不清楚。我们的前期工作发现：1.赤霉素途径抑制蛋白缺失的q-della突变体也对触摸不敏感；2.赤霉素生物合成酶的表达在触摸后的野生型对照中显著下调，而在茉莉酸合成突变体中不变。由此，我们推测，触摸后升高的茉莉酸抑制了赤霉素的生物合成并因此造成植物矮小。本项目将进一步通过赤霉素的精确测定及外源喷施互补实验，明确赤霉素在接触性形态建成中的重要性；并通过核酸-蛋白互作分析深入挖掘茉莉酸抑制赤霉素生物合成的分子机理。该研究将揭示茉莉酸和赤霉素拮抗互作调控接触性形态建成的新机制。