Cuphea wrightii thioesterases have unexpected broad specificities on saturated fatty acids

Cuphea wrightii A. Gray is an herbaceous annual that accumulates 30% caprate (10:0) and 54% laurate (12:0) in seed storage lipids. We investigated the role of acyl-acyl carrier protein (ACP) thioesterases (TE) in acyl chain-length regulation in C. wrightii. Two embryo-derived cDNAs, encoding the TEs Cw FatB1 and Cw FatB2, were isolated. Both proteins were detected in developing embryos and mature seeds but not in other tissues, suggesting involvement in seed oil synthesis. Although expected to be 10:0/12:0-ACP-specific, these genes produced a broad range of fatty acids (12:0, 14:0, and 16:0) in transgenic Arabidopsis with the greatest accumulation at 14:0. Cw FatB2 transformants also accumulated small amounts of 10:0. Because C. wrightii accumulates only ca. 5% 14:0 and ca. 2% 16:0, we tested the possibility that gene dosage effects might significantly alter the overall kinetics of the pathway. Phenotypic comparisons of progeny segregating for the transgenes individually and in a hybrid population demonstrated that increased enzyme pools in vivo had a minor effect on diverting fatty acid production to shorter chains. We propose that Cw FatB1 and Cw FatB2 may be necessary but not sufficient determinants of the C. wrightii phenotype.