MAPPING CANDIDATE SYNTHASE AND THIOESTERASE GENES AND QTL AFFECTING THE SYNTHESIS OF FATTY ACIDS IN CUPHEA SEED OILS: A TALE OF THREE MUTATIONS, TWO GENE FAMILIES, AND PLEIOTROPY

Department of Crop and Soil Science, Oregon State University, Corvallis, OR 97331-3002 USA

Cuphea seed oils (triacylglycerols) are rich sources of saturated medium-chain fatty acids (MCFAs). The primary determinants of MCFA composition are acyl-ACP thioesterases (FATB) and 2-ketoacyl-ACP synthases (KASIV) specific for medium-chain acyl-ACPs. FATB and KASIV are encoded by two gene families in C. viscosissima. As assayed in transgenic plants, Cuphea FATB is necessary and sufficient for the synthesis of MCFAs, whereas Cuphea KASIV alone does not produce MCFA phenotypes, but interacts with FATB to shift the synthesis of fatty acids towards shorter chains. We developed and mapped single-strand conformational polymorphism (SSCP) markers for four FATB and four KASIV loci and mapped three mutations that dramatically affect fatty acid composition (CEI-1, CPR-1, and CPY-1). cei-1 was tightly linked to a FATB locus (~1 cM) and cpr-1 was tightly linked to a KASIV locus (~3 cM) and to cpy-1 (~1 cM). KASIV transcript concentrations were greatly reduced in CPR-1 homozygotes and slightly reduced in CPY-1 homozygotes. FATB protein concentrations were greatly reduced in CPY-1 homozygotes. CEI-1, CPR-1, and CPY-1 had significant allelic and non-allelic interaction effects. The latter were undoutedly caused by the pleiotropic effects of FATB and KASIV genes in overlapping parallel biosynthetic pathways.