title: Cytochrome b5 reductase encoded by CBR1 is essential for a functional male gametophyte in Arabidopsis.
abstract: In all eukaryotes, NADH:cytochrome b5 reductase provides electrons, via cytochrome b5, for a range of biochemical reactions in cellular metabolism, including for fatty acid desaturation in the endoplasmic reticulum. Studies in mammals, yeast, and in vitro plant systems have shown that cytochrome b5 can, at least in some circumstances, also accept electrons from NADPH:cytochrome P450 reductase, potentially allowing for redundancy in reductase function. Here, we report characterization of three T-DNA insertional mutants of the gene encoding cytochrome b5 reductase in Arabidopsis thaliana, CBR1. The progeny of plants heterozygous for the cbr1-2 allele segregated 6% homozygous mutants, while cbr1-3 and cbr1-4 heterozygotes segregated 1:1 heterozygous:wild type, indicating a gametophyte defect. Homozygous cbr1-2 seeds were deformed and required Suc for successful germination and seedling establishment. Vegetative growth of cbr1-2 plants was relatively normal, and they produced abundant flowers, but very few seeds. The pollen produced in cbr1-2 anthers was viable, but when germinated on cbr1-2 or wild-type stigmas, most of the resulting pollen tubes did not extend into the transmitting tract, resulting in a very low frequency of fertilization. These results indicate that cytochrome b5 reductase is not essential during vegetative growth but is required for correct pollen function and seed maturation.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340.
authors.forename: Laura L
authors.initials: LL
authors.lastname: Wayne
authors.forename: James G
authors.initials: JG
authors.lastname: Wallis
authors.forename: Rajesh
authors.initials: R
authors.lastname: Kumar
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Markham
authors.forename: John
authors.initials: J
authors.lastname: Browse
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000378:metabolism*; D020090:Chromosome Segregation / Q000235:genetics; D003433:Crosses, Genetic; D042966:Cytochrome-B(5) Reductase / Q000378:metabolism*; D004269:DNA, Bacterial; D005306:Fertilization; D005816:Genetic Complementation Test; D018525:Germination; D006720:Homozygote; D016254:Mutagenesis, Insertional / Q000235:genetics; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011058:Pollen / Q000166:cytology / Q000201:enzymology* / Q000254:growth & development; D053205:Pollen Tube / Q000166:cytology / Q000201:enzymology / Q000254:growth & development; D012639:Seeds / Q000235:genetics / Q000254:growth & development
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; C036483:T-DNA; C587934:CBR1 protein, Arabidopsis; D042966:Cytochrome-B(5) Reductase