Poster: Secondary metabolism

Abs # 258: Identification of genes involved in tomato volatile synthesis.

Presenter:	Tieman, Denise M., dmtieman@mail.ifas.ufl.edu
Authors	Tieman, Denise M. (A)   Andrew, Hanson D. (A)   Holly, Loucas M. (A)   Eric, Schmelz A. (B)   David, Clark G. (A)   Harry, Klee J. (A)
Affiliations:	(A): University of Florida (B): USDA, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL 32611

The volatile compounds phenylacetaldehyde and 2-phenylethanol are important for the aroma and flavor of ripe tomato fruit. We have identified an L. pennellii introgression line (IL 8-2-1) with greatly increased levels of these compounds in ripe fruit. IL8-2-1 fruit had a distinct floral (rose-like) aroma consistent with the floral aromas of phenylacetaldehyde and 2-phenylethanol. We have used these lines as tools to elucidate the biochemical pathway for the synthesis of phenylacetaldehyde and 2-phenylethanol from phenylalanine. We have isolated genes encoding proteins for the first and last steps in this pathway. The last step in the pathway, the conversion of phenylacetaldehyde to phenylethanol is catalyzed by an alcohol dehydrogenase. Microarrays containing approximately 3,000 tomato cDNAs indicated that an alcohol dehydrogenase gene was more highly expressed in IL8-2-1 fruit than in control M82 fruit. The alcohol dehydrogenase had the highest activity on phenylacetaldehyde as a substrate when expressed in E. coli. The tomato 2-phenylethanol dehydrogenase cDNA was introduced into petunia (cv. Mitchell Diploid) under control of a constitutively expressed promoter. Several transgenic petunia lines had high levels of expression of the tomato gene in flowers. Wild-type petunia flowers emit relatively high levels of phenylacetaldehyde and lower levels of 2-phenylethanol. However, transgenic petunia flowers have higher levels of 2-phenylethanol and lower levels of phenylacetaldehyde than wild-type flowers. Overall, these data indicate that the introduction of the transgene results in the conversion of phenylacetaldehyde to 2-phenylethanol in petunia flowers.