title: LAP5 and LAP6 encode anther-specific proteins with similarity to chalcone synthase essential for pollen exine development in Arabidopsis.
abstract: Pollen grains of land plants have evolved remarkably strong outer walls referred to as exine that protect pollen and interact with female stigma cells. Exine is composed of sporopollenin, and while the composition and synthesis of this biopolymer are not well understood, both fatty acids and phenolics are likely components. Here, we describe mutations in the Arabidopsis (Arabidopsis thaliana) LESS ADHESIVE POLLEN (LAP5) and LAP6 that affect exine development. Mutation of either gene results in abnormal exine patterning, whereas pollen of double mutants lacked exine deposition and subsequently collapsed, causing male sterility. LAP5 and LAP6 encode anther-specific proteins with homology to chalcone synthase, a key flavonoid biosynthesis enzyme. lap5 and lap6 mutations reduced the accumulation of flavonoid precursors and flavonoids in developing anthers, suggesting a role in the synthesis of phenolic constituents of sporopollenin. Our in vitro functional analysis of LAP5 and LAP6 using 4-coumaroyl-coenzyme A yielded bis-noryangonin (a commonly reported derailment product of chalcone synthase), while similar in vitro analyses using fatty acyl-coenzyme A as the substrate yielded medium-chain alkyl pyrones. Thus, in vitro assays indicate that LAP5 and LAP6 are multifunctional enzymes and may play a role in both the synthesis of pollen fatty acids and phenolics found in exine. Finally, the genetic interaction between LAP5 and an anther gene involved in fatty acid hydroxylation (CYP703A2) demonstrated that they act synergistically in exine production.
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637, USA. dobritsa@uchicago.edu
authors.forename: Anna A
authors.initials: AA
authors.lastname: Dobritsa
authors.forename: Zhentian
authors.initials: Z
authors.lastname: Lei
authors.forename: Shuh-Ichi
authors.initials: S
authors.lastname: Nishikawa
authors.forename: Ewa
authors.initials: E
authors.lastname: Urbanczyk-Wochniak
authors.forename: David V
authors.initials: DV
authors.lastname: Huhman
authors.forename: Daphne
authors.initials: D
authors.lastname: Preuss
authors.forename: Lloyd W
authors.initials: LW
authors.lastname: Sumner
mesh_terms: D000217:Acyltransferases / Q000737:chemistry*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019521:Body Patterning / Q000235:genetics; D002599:Chalcone / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002874:Chromosome Mapping; D005227:Fatty Acids / Q000378:metabolism; D044950:Flavanones / Q000096:biosynthesis / Q000737:chemistry; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006900:Hydroxylation; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity / Q000235:genetics; D011058:Pollen / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D048630:Polyketide Synthases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D029681:Arabidopsis Proteins; D005227:Fatty Acids; D044950:Flavanones; C552540:LAP5 protein, Arabidopsis; C552541:LAP6 protein, Arabidopsis; D002599:Chalcone; D048630:Polyketide Synthases; D000217:Acyltransferases; C020141:flavanone synthetase; C005273:naringenin