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, Cc FATB1 and Cc FATB2, 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 Cc FATB1 and Cc FATB2 as medium‐ and long‐chain FATB TE, respectively. Gene expression analysis indicated that Cc FATB1 was seed specific and Cc FATB2 was ubiquitous. Overexpression of Cc FATB1 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 Cc FATB1 and Cw KAS A1, a medium‐chain‐specific ketoacyl‐ACP synthase (KAS) from another 12:0‐rich species, C. wrightii . Overexpression of Cc FATB1 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 Cc FATB2 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.