Molecular Regulation of the Capacity for Isoprene Synthesis in Plants

点击翻译按钮获取中文摘要

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