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 are complex mixtures composed of polyacylated sugars (glucose or sucrose) esterified to branched and straight-chain 4:0 to 12:0 fatty acids. The biogeneses 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 intraspecific F-2 population derived from the cross between L. pennellii LA716 and L. pennellii LA1912 to examine the genetic basis of acylsugar fatty acid composition. Six QTLs were detected which, combined, explain 23-60% of the variance 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 acids that have an even-carbon chain length was found to be primarily determined by a single locus that maps to a location 5.5 cM above TG117 on chromosome 8, QTL function in several cases can be inferred from discrete patterns of fatty acid composition; in other cases, control of acylsugar fatty acid composition appears to be complex.