title: LAP6/POLYKETIDE SYNTHASE A and LAP5/POLYKETIDE SYNTHASE B encode hydroxyalkyl α-pyrone synthases required for pollen development and sporopollenin biosynthesis in Arabidopsis thaliana.
abstract: Plant type III polyketide synthases (PKSs) catalyze the condensation of malonyl-CoA units with various CoA ester starter molecules to generate a diverse array of natural products. The fatty acyl-CoA esters synthesized by Arabidopsis thaliana ACYL-COA SYNTHETASE5 (ACOS5) are key intermediates in the biosynthesis of sporopollenin, the major constituent of exine in the outer pollen wall. By coexpression analysis, we identified two Arabidopsis PKS genes, POLYKETIDE SYNTHASE A (PKSA) and PKSB (also known as LAP6 and LAP5, respectively) that are tightly coexpressed with ACOS5. Recombinant PKSA and PKSB proteins generated tri-and tetraketide α-pyrone compounds in vitro from a broad range of potential ACOS5-generated fatty acyl-CoA starter substrates by condensation with malonyl-CoA. Furthermore, substrate preference profile and kinetic analyses strongly suggested that in planta substrates for both enzymes are midchain- and ω-hydroxylated fatty acyl-CoAs (e.g., 12-hydroxyoctadecanoyl-CoA and 16-hydroxyhexadecanoyl-CoA), which are the products of sequential actions of anther-specific fatty acid hydroxylases and acyl-CoA synthetase. PKSA and PKSB are specifically and transiently expressed in tapetal cells during microspore development in Arabidopsis anthers. Mutants compromised in expression of the PKS genes displayed pollen exine layer defects, and a double pksa pksb mutant was completely male sterile, with no apparent exine. These results show that hydroxylated α-pyrone polyketide compounds generated by the sequential action of ACOS5 and PKSA/B are potential and previously unknown sporopollenin precursors.
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Kim
authors.forename: Etienne
authors.initials: E
authors.lastname: Grienenberger
authors.forename: Benjamin
authors.initials: B
authors.lastname: Lallemand
authors.forename: Che C
authors.initials: CC
authors.lastname: Colpitts
authors.forename: Sun Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Clarice de Azevedo
authors.initials: Cde A
authors.lastname: Souza
authors.forename: Pierrette
authors.initials: P
authors.lastname: Geoffroy
authors.forename: Dimitri
authors.initials: D
authors.lastname: Heintz
authors.forename: Daniel
authors.initials: D
authors.lastname: Krahn
authors.forename: Markus
authors.initials: M
authors.lastname: Kaiser
authors.forename: Erich
authors.initials: E
authors.lastname: Kombrink
authors.forename: Thierry
authors.initials: T
authors.lastname: Heitz
authors.forename: Dae-Yeon
authors.initials: DY
authors.lastname: Suh
authors.forename: Michel
authors.initials: M
authors.lastname: Legrand
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Douglas
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D001704:Biopolymers / Q000096:biosynthesis*; D002338:Carotenoids / Q000096:biosynthesis*; D017343:Genes, Plant; D017403:In Situ Hybridization; D007700:Kinetics; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D011058:Pollen; D048630:Polyketide Synthases / Q000235:genetics*; D011994:Recombinant Proteins / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D029681:Arabidopsis Proteins; D001704:Biopolymers; C552540:LAP5 protein, Arabidopsis; C552541:LAP6 protein, Arabidopsis; D011994:Recombinant Proteins; C009800:sporopollenin; D002338:Carotenoids; D048630:Polyketide Synthases