title: PpASCL, the Physcomitrella patens Anther-Specific Chalcone Synthase-Like Enzyme Implicated in Sporopollenin Biosynthesis, Is Needed for Integrity of the Moss Spore Wall and Spore Viability.
abstract: Sporopollenin is the main constituent of the exine layer of spore and pollen walls. The anther-specific chalcone synthase-like (ASCL) enzyme of Physcomitrella patens, PpASCL, has previously been implicated in the biosynthesis of sporopollenin, the main constituent of exine and perine, the two outermost layers of the moss spore cell wall. We made targeted knockouts of the corresponding gene, PpASCL, and phenotypically characterized ascl sporophytes and spores at different developmental stages. Ascl plants developed normally until late in sporophytic development, when the spores produced were structurally aberrant and inviable. The development of the ascl spore cell wall appeared to be arrested early in microspore development, resulting in small, collapsed spores with altered surface morphology. The typical stratification of the spore cell wall was absent with only an abnormal perine recognisable above an amorphous layer possibly representing remnants of compromised intine and/or exine. Equivalent resistance of the spore walls of ascl mutants and the control strain to acetolysis suggests the presence of chemically inert, defective sporopollenin in the mutants. Anatomical abnormalities of late-stage ascl sporophytes include a persistent large columella and an air space incompletely filled with spores. Our results indicate that the evolutionarily conserved PpASCL gene is needed for proper construction of the spore wall and for normal maturation and viability of moss spores.
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Rhys M
authors.initials: RM
authors.lastname: Daku
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Fazle
authors.initials: F
authors.lastname: Rabbi
authors.affiliation: Department of Biology, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Josef
authors.initials: J
authors.lastname: Buttigieg
authors.affiliation: Department of Geology, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Coulson
authors.affiliation: BioImaging Facility, University of British Colombia, Vancouver, British Columbia, Canada.
authors.forename: Derrick
authors.initials: D
authors.lastname: Horne
authors.affiliation: BioImaging Facility, University of British Colombia, Vancouver, British Columbia, Canada.
authors.forename: Garnet
authors.initials: G
authors.lastname: Martens
authors.affiliation: Department of Biology, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Neil W
authors.initials: NW
authors.lastname: Ashton
authors.affiliation: Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan, Canada.
authors.forename: Dae-Yeon
authors.initials: DY
authors.lastname: Suh
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D001704:Biopolymers / Q000096:biosynthesis*; D044002:Bryophyta / Q000201:enzymology; D019068:Bryopsida / Q000201:enzymology*; D002338:Carotenoids / Q000096:biosynthesis*; D002473:Cell Wall / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified; D016133:Polymerase Chain Reaction; D013170:Spores / Q000502:physiology*
chemical_list: D001704:Biopolymers; D010940:Plant Proteins; C009800:sporopollenin; D002338:Carotenoids; D000217:Acyltransferases; C020141:flavanone synthetase