Identification of QTLs controlling acylsugar fatty acid composition in an intraspecific population of Lycopersicon pennellii (Corr.) D'Arcy

Acylsugars exuded by type IV glandular trichomes are responsible for insect resistances found in many Lycopersicon pennellii accessions. Acylsugars ar e complex mixtures composed of polyacylated sugars (glucose or sucrose) est erified to branched and straight-chain 4:0 to 12:0 fatty acids. The biogene ses of these unusual fatty acid constituents have their origins in branched -chain amino acid pathways. However, the mechanism of fatty acid elongation in these systems and the genetic control of carbon flux from amino acid to fatty acid pathways remain unclear. In this study, we used an intraspecifi c F-2 population derived from the cross between L. pennellii LA716 and L. p ennellii LA1912 to examine the genetic basis of acylsugar fatty acid compos ition. Six QTLs were detected which, combined, explain 23-60% of the varian ce observed for each of the nine segregating fatty acid constituents. Both correlation data and QTL analysis data indicate that branched medium-chain fatty acids are synthesized through elongation of short-chain precursors in two-carbon increments. The proportion of iso-branched acylsugar fatty acid s that have an even-carbon chain length was found to be primarily determine d by a single locus that maps to a location 5.5 cM above TG117 on chromosom e 8, QTL function in several cases can be inferred from discrete patterns o f fatty acid composition; in other cases, control of acylsugar fatty acid c omposition appears to be complex.