Molecular and Biochemical Determinants of Floral Scent Production in Antirrhinum majus

挥发性化合物在植物中作为昆虫引诱剂、驱虫剂和信号分子发挥着重要的作用。花香是植物-昆虫相互作用的关键调节因子，在授粉成功，从而在许多作物的果实发育中发挥着核心作用。尽管花香对植物繁殖具有重要的经济意义，但人们对花香挥发物产生的分子机制知之甚少。这项建议的目标是使用分子、遗传和生化方法来了解如何利用花香作为模型系统来控制植物中挥发性物质的产生。虽然香气挥发性化合物的生产在植物界似乎非常普遍，但关于它们的生物合成和调控的信息有限，到目前为止都是基于对单一模型系统-clarkia的分析。蜜蜂授粉的金鱼草(Snapgon)将被用作本研究的模型系统，因为它具有与Clarkia系统相比的重要优势，如完善的遗传图谱、转座子基因克隆系统、可用的转化方案和有节奏的发射。花香通常是低分子量化合物的复杂混合物，主要分布在三类化合物中：脂肪酸衍生物、苯类化合物和异戊二烯类化合物。这类化合物的酯在许多植物物种中是最常见的，在这些物种中，它们对总花香产量有很大贡献。然而，控制植物挥发酯生物合成的生化途径、酶和基因却鲜有人关注。建议的研究重点是挥发性甲酯苯甲酸酯的合成分子机理，甲基苯甲酸酯是一种重要的昆虫引诱剂，也是金鱼草花香的主要成分。这项研究专门解决了植物如何调节挥发性酯的产生以及授粉和昼夜节律如何在分子水平上影响气味排放的问题。克隆的S-腺苷-L-甲硫氨酸-苯甲酸羧甲基转移酶(BAMT)是苯甲酸甲酯生物合成的最后一种酶，它的出现为详细研究花香产生的调控提供了一个独特的机会。在花发育过程中，BAMT基因在不同组织中的表达模式将被确定，以确定参与调控苯甲酸甲酯释放的分子机制(转录、翻译或翻译后)。将特别注意排放苯甲酸甲酯的金鱼草品种与非排放植物的比较分析。为了确定导致植物授粉后香气产生变化的特定分子和生化机制，将在授粉后的不同时间测定BAMT mRNA、BAMT蛋白、BAMT活性、BAMT活性、BAMT释放以及细胞内可能积累的甲基苯甲酸。总体而言，这项研究将对理解氯味形成的基本过程做出重大贡献。虽然这一建议主要是为了解决有关控制植物中挥发性物质产生的分子机制的基本问题，但所获得的结果最终可能会在农业和园艺中得到应用。在这些研究中获得的对代谢途径(包括发育变化和亚细胞区划)的酶学和调控的了解，将为工程植物改善气味质量提供知识，以增加传粉者对花的吸引，从而提高重要农作物的产量。

Volatile compounds play an important role in plants as insect attractants,repellents and signal molecules. Floral scent is a key modulating factorin plant-insect interactions and plays a central role in successful pollination, and thus in fruit development of many crop species. Despitethe economic importance of floral scent for plant reproduction, little isknown about the molecular mechanisms involved in the production of floral volatiles. The objectives of this proposal are to use molecular, genetic,and biochemical approaches to understand how production of volatiles couldbe manipulated in plants using floral scent as a model system. Althoughproduction of scent volatile compounds appears to be very widespread in theplant kingdom, the information about their biosynthesis and regulation islimited and based to date on the analysis of a single model system -Clarkia. Bee-pollinated Antirrhinum majus (snapdragon) will be used as amodel system for this study due to its important advantages over theClarkia system such as a well developed genetic map, transposon genecloning system, available transformation protocol, and rhythmic emission.Floral scent is often a complex mixture of low molecular weight compounds,which are mainly distributed within three groups: fatty acid derivatives,benzenoids and isoprenoids. Esters of such compounds are among the most common in many plant species where they contribute significantly to thetotal floral scent output. However, the biochemical pathways, enzymes andgenes controlling the biosynthesis of volatile esters in plants have received little attention. The focus of the proposed research is on themolecular mechanisms of the synthesis of the volatile ester methylbenzoate,an important insect attractant and a major component of snapdragon floral scent. This research specifically addresses the questions of how plantsregulate the production of volatile esters and how pollination andcircadian rhythm affect scent emission at the molecular level. Theavailability of a cloned S-adenosyl-L-methionine:benzoic acid carboxylmethyltransferase (BAMT), the final enzyme in the biosynthesis ofmethylbenzoate, recently isolated in the PI's lab, provides a uniqueopportunity to make a detailed study of the regulation of floral scentproduction. The mode of expression of BAMT gene will be characterized indifferent tissues during flower development to determine the molecularmechanisms (transcriptional, translational or post-translational) involvedin the regulation of methylbenzoate emission. Special attention will bepaid to comparative analyses of Antirrhinum varieties that emitmethylbenzoate with non-emitting plants. To determine the specific molecular and biochemicalmechanisms that are responsible for the postpollination changes in floral scent production inplants, the levels of BAMT mRNA, BAMT protein, BAMT activity, emission, andthe possible accumulation of methylbenzoate inside the cells will bedetermined at different times after pollination. Overall, this researchwill lead to significant contributions to understanding of the fundamental processes underlying the formation offloral scent. While this proposal is designed primarily to addressfundamental questions about molecular mechanisms controlling production of volatiles in plants, the results obtained may ultimately find applicationin agriculture and horticulture. An understanding of the enzymology andregulation of metabolic pathways (including developmental changes and subcellular compartmentation), obtained in these studies, will provide theknowledge for engineering plants with improved scent quality to increasethe attraction of pollinators to flowers and thereby increase the yield of important agricultural crops.