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Secondary Metabolism

Morant, Marc [1], Jørgensen, Kirsten [1], Schaller, Hubert [2], Pinot, Franck [3], Møller, Birger L. [1], Werck-Reichhart, Danièle [3], Bak, Søren [1].

CYP703: an ancient cytochrome P450 in land plants catalyzing the C-7 hydroxylation of lauric acid for sporopollenin formation in pollen.

CYP703 is a cytochrome P450 family specific to land plants. Typically each plant species contains a single CYP703. Arabidopsis thaliana CYP703A2 is expressed in the anthers of developing flowers. Expression is initiated at the tetrad stage and restricted to microspores and to the tapetum cell layer. A. thaliana CYP703A2 knockout lines showed impaired pollen development and a partial male sterile phenotype. Scanning electron microscopy and transmission electron microscopy of pollen from the knockout plants showed an impaired pollen wall development with absence of exine. The fluorescent layer around the pollen grains ascribed to the presence of phenylpropanoid units in sporopollenin was absent in the CYP703A2 knockout lines. Heterologous expression of CYP703A2 in yeast cells demonstrated that CYP703 catalyzes the conversion of medium chain saturated fatty acids to the corresponding mono-hydroxylated fatty acids with a preferential hydroxylation of lauric acid at the C-7 position. Incubation of recombinant CYP703 with methanol extracts from developing flowers confirmed that lauric acid and 7-hydroxy lauric acid are the in planta substrate and product, respectively. The data demonstrate that 7-hydroxy-lauric acid is an essential building block in sporopollenin formation to form ester and ether linkages with phenylpropanoids units. This identifies CYP703 as the first P450 family specifically involved in pollen development.


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1 - University of Copenhagen, Department of Plant Biology, Thorvaldsensvej 40, Frederiksberg, 1871, Denmark
2 - Institute of Plant Molecular Biology, Department of plant isoprenoids, 28 rue Goethe, Strasbourg, 67083, France
3 - Institute of Plant Molecular Biology, Department of Plant Metabolic Responses, 28 rue Goethe, Strasbourg, 67083, France

Keywords:
exine
pollen
cytochrome P450.

Presentation Type: ASPB Minisymposium
Session: M21
Location: Continental C/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:35 PM
Number: M21004
Abstract ID:700


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