A Cuphea beta-ketoacyl-ACP synthase shifts the synthesis of fatty acids towards shorter chains in Arabidopsis seeds expressing Cuphea FatB thioesterases.
Acyl-acyl carrier protein (ACP) thioesterases with specificities on medium chain substrates (C8-C14) are requisite enzymes in plants that produce 8:0, 10:0, 12:0 and 14:0 seed oils, but they may not be the sole enzymatic determinants of chain length. The contribution to chain length regulation of a beta-ketoacyl-ACP synthase, Cw KAS A1, derived from Cuphea wrightii, a species that accumulates 30% 10:0 and 54% 12:0 in seed oils, was investigated. Expression of Cw KAS A1 in Arabidopsis seeds reduced 16:0 from 8.2 to 6.2 mol%, suggesting a KAS II-type activity. In the presence of the KAS I inhibitor cerulenin, however, transgenic seed extracts extended 6:0- and 8:0-ACP at a rate four- to fivefold greater than extracts from untransformed plants, whereas no difference was observed in extension of 14:0- and 16:0-ACP. The effect of KAS A1 on seed oils was tested by combining it with the C. wrightii medium chain-specific thioesterases, Cw FatB1 and Cw FatB2, in crosses of transformed plants. Fatty acid synthesis thesis shifted towards shorter chains in progeny expressing both classes of enzymes. KasA1/FatB1 homozygotes produced threefold more 12:0 than the FatB1 parent while 14:0 and 16:0 were reduced by one-third and one-half, respectively. F2 progeny expressing KasA1 and FatB2 produced twofold more 10:0 and 1.4-fold more 12:0 than the FatB2 parent, and the double-transgenic progeny produced one-quarter less 14:0 and one-half less 16:0 than the FatB2 parent. It is hypothesized that the shift towards production of shorter chains resulted from increased pools of medium chain acyl-ACP resulting from KAS A1 activity. The combined activities of KAS A1 and FatB thioesterases appear to determine the C. wrightii phenotype.
Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, USA.
J M
JM
Leonard
S J
SJ
Knapp
M B
MB
Slabaugh
D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins; D005227:Fatty Acids / Q000096:biosynthesis* / Q000737:chemistry; D015870:Gene Expression; D017343:Genes, Plant; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins; D030821:Plants, Genetically Modified; D012639:Seeds / Q000201:enzymology; D013379:Substrate Specificity; D013869:Thiolester Hydrolases / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D005227:Fatty Acids; D007527:Isoenzymes; D010940:Plant Proteins; C078182:beta-ketoacyl-acyl carrier protein synthase I; D015099:3-Oxoacyl-(Acyl-Carrier-Protein) Synthase; C490837:FATB1 protein, Arabidopsis; D013869:Thiolester Hydrolases