1. PpASCL, a moss ortholog of anther-specific chalcone synthase-like enzymes, is a hydroxyalkylpyrone synthase involved in an evolutionarily conserved sporopollenin biosynthesis pathway.
- Author
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Colpitts CC, Kim SS, Posehn SE, Jepson C, Kim SY, Wiedemann G, Reski R, Wee AGH, Douglas CJ, and Suh DY
- Subjects
- Amino Acid Sequence, Arabidopsis enzymology, Arabidopsis genetics, Biocatalysis, Biopolymers chemistry, Biosynthetic Pathways, Bryopsida genetics, Carotenoids chemistry, Catalytic Domain, Chromatography, Thin Layer, Conserved Sequence, Gene Expression Regulation, Plant, Genes, Plant genetics, Intramolecular Oxidoreductases chemistry, Kinetics, Models, Molecular, Molecular Sequence Data, Oligonucleotide Array Sequence Analysis, Organ Specificity, Polyketide Synthases chemistry, Polyketide Synthases metabolism, Pyrones chemistry, Pyrones metabolism, Sequence Alignment, Sequence Homology, Amino Acid, Spores genetics, Substrate Specificity, Acyltransferases chemistry, Acyltransferases metabolism, Biopolymers biosynthesis, Bryopsida enzymology, Carotenoids biosynthesis, Evolution, Molecular, Flowers enzymology, Intramolecular Oxidoreductases metabolism
- Abstract
Sporopollenin is the main constituent of the exine layer of spore and pollen walls. Recently, several Arabidopsis genes, including polyketide synthase A (PKSA), which encodes an anther-specific chalcone synthase-like enzyme (ASCL), have been shown to be involved in sporopollenin biosynthesis. The genome of the moss Physcomitrella patens contains putative orthologs of the Arabidopsis sporopollenin biosynthesis genes. We analyzed available P.patens expressed sequence tag (EST) data for putative moss orthologs of the Arabidopsis genes of sporopollenin biosynthesis and studied the enzymatic properties and reaction mechanism of recombinant PpASCL, the P.patens ortholog of Arabidopsis PKSA. We also generated structure models of PpASCL and Arabidopsis PKSA to study their substrate specificity. Physcomitrella patens orthologs of Arabidopsis genes for sporopollenin biosynthesis were found to be expressed in the sporophyte generation. Similarly to Arabidopsis PKSA, PpASCL condenses hydroxy fatty acyl-CoA esters with malonyl-CoA and produces hydroxyalkyl α-pyrones that probably serve as building blocks of sporopollenin. The ASCL-specific set of Gly-Gly-Ala residues predicted by the models to be located at the floor of the putative active site is proposed to serve as the opening of an acyl-binding tunnel in ASCL. These results suggest that ASCL functions together with other sporophyte-specific enzymes to provide polyhydroxylated precursors of sporopollenin in a pathway common to land plants., (© 2011 The Authors. New Phytologist © 2011 New Phytologist Trust.)
- Published
- 2011
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