Rs. Van Der Hoeven et al., Genetic control and evolution of sesquiterpene biosynthesis in Lycopersicon esculentum and L-hirsutum, PL CELL, 12(11), 2000, pp. 2283-2294
Segregation analysis between Lysopersicon esculentum (cultivated tomato) an
d L. hirsutum (wild form) in conjunction with positional verification by us
ing near-isogenic lines demonstrated that biosynthesis of two structurally
different classes of sesquiterpenes in these species is controlled by loci
on two different chromosomes. A locus on chromosome 6, Sesquiterpene syntha
se1 (Sst1), was identified for which the L. esculentum allele is associated
with the biosynthesis of beta -caryophyllene and alpha -humulene. At this
same locus, the L. hirsutum allele is associated with biosynthesis of germa
crene B, germacrene D, and an unidentified sesquiterpene. Genomic mapping,
cDNA isolation, and heterologous expression of putative sesquiterpene synth
ases from both L. esculentum and L. hirsutum revealed that Sst1 is composed
of two gene clusters 24 centimorgans apart, Sst1-A and Sst1-B, and that on
ly the genes in the Sst1-A cluster are responsible for accumulation of chro
mosome 6-associated sesquiterpenes. At a second locus, Sst2, on chromosome
8, the L. hirsutum allele specified accumulation of alpha -santalene, alpha
-bergamotene, and beta -bergamotene. Surprisingly, the L. esculentum allel
e for Sst2 is not associated with the expression of any sesquiterpenes, whi
ch suggests that cultivated tomato may have a nonfunctional allele. Sesquit
erpene synthase cDNA clones on chromosome 6 do not cross-hybridize on genom
ic DNA gel blots with putative sesquiterpene synthases on chromosome 8, an
indication that the genes in Sst1 and Sst2 are highly diverged, each being
responsible for the biosynthesis of structurally different sets of sesquite
rpenes.