Improved stearate phenotype in transgenic canola expressing a modified acyl-acyl carrier protein thioesterase
Marc T. Facciotti1, Paul B. Bertain3
& Ling Yuan2
3
Calgene, LLC, Davis, CA 95616.
1
Present address: The Graduate Group in Biophysics, University of California at Berkeley, Berkeley, CA 94720.
2
Present address: Maxygen, Redwood City, CA 94063.
Correspondence should be addressed to Ling Yuan ling_yuan@maxygen.comalanine scanningsite-directed mutagenesisstearatetransgenic plantsprotein engineering
The engineering of crops for selected fatty acid production is one of the major goals of plant biotechnology. The Garm FatA1, an acyl-acyl carrier protein (ACP) thioesterase isolated from Garcinia mangostana, generates an elevated stearate (18:0) phenotype in transgenic Brassica plants. By site-directed mutagenesis, we generated seven mutants that showed up to a 13-fold increase in specific enzyme activity toward 18:0-ACP in vitro. The seed-specific expression of mutant S111A/V193A in Brassica plants results in transgenic plants that accumulate 55−68% more stearate than plants expressing the wild-type enzyme. Our results demonstrate that a thioesterase can be engineered to increase specific activity and that its improved function demonstrated in vitro is retained in vivo.
