title: CYP704B1 is a long-chain fatty acid omega-hydroxylase essential for sporopollenin synthesis in pollen of Arabidopsis.
abstract: Sporopollenin is the major component of the outer pollen wall (exine). Fatty acid derivatives and phenolics are thought to be its monomeric building blocks, but the precise structure, biosynthetic route, and genetics of sporopollenin are poorly understood. Based on a phenotypic mutant screen in Arabidopsis (Arabidopsis thaliana), we identified a cytochrome P450, designated CYP704B1, as being essential for exine development. CYP704B1 is expressed in the developing anthers. Mutations in CYP704B1 result in impaired pollen walls that lack a normal exine layer and exhibit a characteristic striped surface, termed zebra phenotype. Heterologous expression of CYP704B1 in yeast cells demonstrated that it catalyzes omega-hydroxylation of long-chain fatty acids, implicating these molecules in sporopollenin synthesis. Recently, an anther-specific cytochrome P450, denoted CYP703A2, that catalyzes in-chain hydroxylation of lauric acid was also shown to be involved in sporopollenin synthesis. This shows that different classes of hydroxylated fatty acids serve as essential compounds for sporopollenin formation. The genetic relationships between CYP704B1, CYP703A2, and another exine gene, MALE STERILITY2, which encodes a fatty acyl reductase, were explored. Mutations in all three genes resulted in pollen with remarkably similar zebra phenotypes, distinct from those of other known exine mutants. The double and triple mutant combinations did not result in the appearance of novel phenotypes or enhancement of single mutant phenotypes. This implies that each of the three genes is required to provide an indispensable subset of fatty acid-derived components within the sporopollenin biosynthesis framework.
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: Jay
authors.initials: J
authors.lastname: Shrestha
authors.forename: Marc
authors.initials: M
authors.lastname: Morant
authors.forename: Franck
authors.initials: F
authors.lastname: Pinot
authors.forename: Michiyo
authors.initials: M
authors.lastname: Matsuno
authors.forename: Robert
authors.initials: R
authors.lastname: Swanson
authors.forename: Birger Lindberg
authors.initials: BL
authors.lastname: Møller
authors.forename: Daphne
authors.initials: D
authors.lastname: Preuss
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D055162:Biocatalysis; D001704:Biopolymers / Q000096:biosynthesis*; D002338:Carotenoids / Q000096:biosynthesis*; D002874:Chromosome Mapping; D042926:Cytochrome P-450 CYP4A / Q000235:genetics / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D006900:Hydroxylation; D009154:Mutation / Q000235:genetics; D009928:Organ Specificity; D010636:Phenols / Q000378:metabolism; D010641:Phenotype; D011058:Pollen / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; D001704:Biopolymers; D005227:Fatty Acids; D010636:Phenols; C009800:sporopollenin; D002338:Carotenoids; D042926:Cytochrome P-450 CYP4A
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