Biosynthesis of phytosterol esters: identification of a sterol o-acyltransferase in Arabidopsis.
Fatty acyl esters of phytosterols are a major form of sterol conjugates distributed in many parts of plants. In this study we report an Arabidopsis (Arabidopsis thaliana) gene, AtSAT1 (At3g51970), which encodes for a novel sterol O-acyltransferase. When expressed in yeast (Saccharomyces cerevisiae), AtSAT1 mediated production of sterol esters enriched with lanosterol. Enzyme property assessment using cell-free lysate of yeast expressing AtSAT1 suggested the enzyme preferred cycloartenol as acyl acceptor and saturated fatty acyl-Coenyzme A as acyl donor. Taking a transgenic approach, we showed that Arabidopsis seeds overexpressing AtSAT1 accumulated fatty acyl esters of cycloartenol, accompanied by substantial decreases in ester content of campesterol and beta-sitosterol. Furthermore, fatty acid components of sterol esters from the transgenic lines were enriched with saturated and long-chain fatty acids. The enhanced AtSAT1 expression resulted in decreased level of free sterols, but the total sterol content in the transgenic seeds increased by up to 60% compared to that in wild type. We conclude that AtSAT1 mediates phytosterol ester biosynthesis, alternative to the route previously described for phospholipid:sterol acyltransferase, and provides the molecular basis for modification of phytosterol ester level in seeds.
Chen
Qilin
Q
Plant Biotechnology Institute, National Research Council Canada, Saskatoon, Saskatchewan, Canada S7N 0W9.
Steinhauer
Lee
L
Hammerlindl
Joe
J
Keller
Wilf
W
Zou
Jitao
J
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010840:Phytosterols / Q000096:biosynthesis*; D002785:Sterol O-Acyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013261:Sterols / Q000096:biosynthesis / Q000737:chemistry; D013379:Substrate Specificity
D029681:Arabidopsis Proteins; D010840:Phytosterols; D013261:Sterols; C525661:SAT1 protein, Arabidopsis; D002785:Sterol O-Acyltransferase