Molecular Regulation of the Capacity for Isoprene Synthesis in Plants

异戊二烯是由许多植物，尤其是树木排放出来的。异戊二烯的排放对大气化学有很大的影响，因此人们对其排放进行了广泛的研究，但尚未确定其排放速率的调节机制。植物释放的异戊二烯随温度和光照变化很大。提出了实验来检验几种关于如何调节植物异戊二烯排放速率的假设。短期调节将通过测量光或温度变化之前、期间和之后的代谢物来研究。控制异戊二烯瞬时释放速率的因素将通过分析(1)瞬时代谢产物水平的变化和(2)对异戊二烯合成途径中取食中间体的反应来评估。为了跟踪来自内源性光合作用代谢物和来自外源性中间体的异戊二烯，波恩大学的同事将使用一种基于激光的光声系统来检测氘化中间体中氘标记的异戊二烯。长期诱导现象将在(1)从未产生异戊二烯的叶片和(2)通过将植株移至低温弱光环境而降低异戊二烯排放能力的叶片中进行研究。异戊二烯合成途径的前体代谢物水平、酶活性和转录物丰度的变化将包括在分析中。最后，对异戊二烯排放能力演化的步骤进行了研究。这将涉及两种方法。首先，从豆科葛中提取的异戊二烯合成酶将通过组成启动子、自身启动子和热休克启动子转化为拟南芥。将评估异戊二烯合成酶和其他异戊二烯合成途径中选定基因的表达和活性的调控，以确定不释放异戊二烯的植物是否通常具有依赖光和热的异戊二烯释放所需的调控机制。其次，通过分析异戊二烯合成酶的晶体结构来确定异戊二烯合成酶与类似倍半萜合成酶的区别。这些研究将提供关于异戊二烯合成调控的基本信息，从而允许改变植物的异戊二烯合成。可能需要对植物或细菌进行改造，以产生经济上有用的异戊二烯量，或者对树木种植中使用的树木进行改造，使它们不产生异戊二烯。这些研究还将用于帮助预测植物的异戊二烯排放，这将提高我们预测大气臭氧产生的能力

Isoprene is emitted from many plants, especially trees. Isoprene emission has large effects on atmospheric chemistry and so its emission has been extensively studied but mechanisms of regulation of the rate of emission have not yet been determined. Isoprene emission from plants varies substantially with temperature and light. Experiments are proposed to test several hypotheses about how the rate of isoprene emission from plants is regulated. Short term regulation will be studied by measuring metabolites before, during, and after a change in light or temperature. The factors that control the instantaneous rate of isoprene emission will be assessed by analyzing (1) changes in metabolite levels during transients and (2) responses to feeding intermediates of the isoprene synthesis pathway. To keep track of isoprene coming from endogenous photosynthesis metabolites and that coming from exogenous intermediates, a laser-based photoacoustic system for detecting deuterium labeled isoprene from deuterated intermediates will be used by colleagues at the University of Bonn. Longer term induction phenomena will be studied in (1) leaves that have never made isoprene and in (2) leaves where the isoprene emission capacity has been reduced by moving the plants into low temperature and low light. Changes in precursor metabolite levels, enzyme activity, and transcript abundance for selected enzymes of the isoprene synthesis pathway will be included in the analysis. Finally, the steps required for the evolution of the capacity for isoprene emission will be studied. This will involve two approaches. First, isoprene synthase from the legume kudzu will be transformed into Arabidopsis on a constitutive promoter, on its own promoter, and on a heat-shock promoter. The regulation of the expression and activity of isoprene synthase and other selected genes in the isoprene synthesis pathway will be assessed to determine if non-emitting plants normally have the regulatory mechanisms needed for light and heat-dependent isoprene emission. Second, the differences between isoprene synthase and a similar sesquiterpene synthase will be determined by analyzing the crystal structure of isoprene synthase. These studies will provide basic information on regulation of isoprene synthesis to allow for altering isoprene synthesis by plants. It may be desirable to engineer plants or bacteria to make economically useful amounts of isoprene or it might be useful to engineer trees used in tree farming so that they do not produce isoprene. These studies will also be used to help predict isoprene emission from plants, which will improve our ability to predict atmospheric ozone production