title: PpASCL, a moss ortholog of anther-specific chalcone synthase-like enzymes, is a hydroxyalkylpyrone synthase involved in an evolutionarily conserved sporopollenin biosynthesis pathway.
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.
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Che C
authors: CC
authors: Colpitts
authors: Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
authors: Sung Soo
authors: SS
authors: Kim
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Sarah E
authors: SE
authors: Posehn
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Christina
authors: C
authors: Jepson
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Sun Young
authors: SY
authors: Kim
authors: Plant Biotechnology, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
authors: Gertrud
authors: G
authors: Wiedemann
authors: Plant Biotechnology, Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.|Freiburg Institute for Advanced Studies, University of Freiburg, 79104 Freiburg, Germany.
authors: Ralf
authors: R
authors: Reski
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Andrew G H
authors: AGH
authors: Wee
authors: Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
authors: Carl J
authors: CJ
authors: Douglas
authors: Department of Chemistry and Biochemistry, University of Regina, Regina, SK S4S 0A2, Canada.
authors: Dae-Yeon
authors: DY
authors: Suh
mesh_terms: D000217:Acyltransferases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D055162:Biocatalysis; D001704:Biopolymers / Q000096:biosynthesis* / Q000737:chemistry; D053898:Biosynthetic Pathways; D019068:Bryopsida / Q000201:enzymology* / Q000235:genetics; D002338:Carotenoids / Q000096:biosynthesis* / Q000737:chemistry; D020134:Catalytic Domain; D002855:Chromatography, Thin Layer; D017124:Conserved Sequence; D019143:Evolution, Molecular; D035264:Flowers / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D019746:Intramolecular Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D009928:Organ Specificity; D048630:Polyketide Synthases / Q000737:chemistry / Q000378:metabolism; D011753:Pyrones / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013170:Spores / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D001704:Biopolymers; D011753:Pyrones; C009800:sporopollenin; D002338:Carotenoids; D048630:Polyketide Synthases; D000217:Acyltransferases; C020141:flavanone synthetase; D019746:Intramolecular Oxidoreductases