Molecular and Biochemical Determinants of Floral Scent Production in Antirrhinum majus

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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.