New FATB thioesterases from a high‐laurate Cuphea species: Functional and complementation analyses

The New World genus Cuphea is a rich source of genes encoding enzymes specialized for seed‐specific synthesis of short‐ and medium‐chain fatty acids (FA). We isolated and characterized two new acyl‐acyl carrier protein (ACP) thioesterase (TE) cDNA, CcFATB1 and CcFATB2, from developing seeds of C. calophylla var. mesostemon. Cuphea calophylla is one of several species in the genus specializing in the synthesis of lauric acid (12:0). Phylogenetic clustering classified CcFATB1 and CcFATB2 as medium‐ and long‐chain FATB TE, respectively. Gene expression analysis indicated that CcFATB1 was seed specific and CcFATB2 was ubiquitous. Overexpression of CcFATB1 in developing seeds of Arabidopsis partially redirected FA synthesis toward medium‐chain FA (12:0, 14:0, and 16:0). Laurate synthesis was preferentially increased by co‐expressing CcFATB1 and CwKAS A1, a medium‐chain‐specific ketoacyl‐ACP synthase (KAS) from another 12:0‐rich species, C. wrightii. Overexpression of CcFATB1 cDNA complemented the low‐palmitate (16:0) but not the low‐stearate (18:0) phenotype in leaves and seeds of an Arabidopsis fatb‐2 mutant, whereas CcFATB2 restored both long‐chain FA. The investigated Cuphea species provide a diverse source of seed‐specific FATB and KAS genes for combinatorial manipulation of medium‐chain FA content in oilseed plants.