MOLECULAR AND GENETIC ANALYSIS OF SESQUITERPENE BIOSYNTHESIS IN Lycopersicon esculentum CV. E6230 AND Lycopersicon hirsutum LA1777

¹ Cornell University Department of Plant Breeding 252 Emerson Hall Ithaca NY 14850 USA

² Novartis Agribusiness Biotechnology Research, Inc. 3054 Cornwallis Road Research Triangle Park NC 27709-2257 USA

Sesquiterpenes are ubiquitous secondary metabolites, implicated in plant defense against insect herbivores and microbial pathogens. The biosynthesis of two structurally different sesquiterpene classes in tomato was shown, by segregation analysis and positional verification using near-isogenic lines, to be controlled by two genomic regions. A locus on the top of chromosome 6 was associated with the biosynthesis of the structurally related germacrenes B and D in L. hirsutum LA1777, and beta-caryophyllene and alpha-humulene in L. esculentum. Another locus on chromosome 8 cosegregated with accumulation of alpha-santalene, alpha-bergamotene and beta-bergamotene. Heterologous expression of two putative sesquiterpene cyclase cDNAs isolated from L. hirsutum, and two others from L. esculentum confirmed that the L. hirsutum genes are responsible for biosynthesis of the germacrenes and the L. esculentum genes for beta-caryophyllene and alpha-humulene. When using the sesquiterpene cyclases as a probe on genomic Southerns, a multigene family divided over two clusters containing 6 copies of the gene was detected on chromosome 6. Interestingly, Southern analysis of the sesquiterpene cyclases from chromosome 6 did not yield any restriction fragments cosegregating with the chromosome 8 associated sesquiterpenes. We propose that there are two widely diverged classes of sequiterpene cyclases in Lycopersicon hirsutum and likely all Lycopersicon species on chromosome 6 and 8 respectively, each responsible for the biosynthesis of structurally different sets of sesquiterpenes.