title: An Arabidopsis mutant that is resistant to the protoporphyrinogen oxidase inhibitor acifluorfen shows regulatory changes in tetrapyrrole biosynthesis.
abstract: Several Arabidopsis mutants of the ecotype Dijon were isolated that show resistance to the herbicide acifluorfen, which inactivates protoporphyrinogen oxidase (PPOX), an enzyme of tetrapyrrole biosynthesis. This enzyme provides protoporphyrin for both Mg chelatase and ferrochelatase at the branchpoint, which leads to chlorophyll and heme, respectively. One of the mutations, aci5-3, displays semidominant inheritance. Heterozygous progeny showed yellow-green leaves, while the homozygous seedlings were white and inviable, but could be rescued by supplementing the medium with sugar. Interestingly, the expression of neither of the two forms of PPOX was altered in the mutant, but the rate of synthesis of 5-aminolevulinate, the precursor of all tetrapyrroles, was drastically reduced. Genetic mapping revealed the mutant locus is closely linked to the ch42 marker, which is itself located in the CHLI-1 gene which codes for one of the three subunits of Mg chelatase. The cs mutant also shows a defect in this gene, and test for allelism with aci5-3 confirmed that the two mutations are allelic. Sequencing of the wild type and aci5-3 alleles of CHLI-1 revealed a single base change (G718A), which results in a D240N substitution in the CHLI-1 protein. In the homozygous aci5-3 mutant no CHLI-1 RNA or protein could be detected. Strikingly, CHLH and CHLI-2 transcripts were also absent. This indicates the existence of a feedback-regulatory mechanism that inactivates the genes encoding certain Mg chelatase subunits. The basis for the semidominant inheritance pattern and the relationship between herbicide resistance and modified gene expression is discussed.
authors.affiliation: Department of Genetics, Faculty of Biology, M.V. Lomonosov State University, Leninskie Gori 1, Building 12, 119899, Moscow, Russia.
authors.forename: Olga
authors.initials: O
authors.lastname: Soldatova
authors.forename: Alexey
authors.initials: A
authors.lastname: Apchelimov
authors.forename: Natalia
authors.initials: N
authors.lastname: Radukina
authors.forename: Tatiana
authors.initials: T
authors.lastname: Ezhova
authors.forename: Sergey
authors.initials: S
authors.lastname: Shestakov
authors.forename: Valeria
authors.initials: V
authors.lastname: Ziemann
authors.forename: Boris
authors.initials: B
authors.lastname: Hedtke
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
mesh_terms: D000622:Aminolevulinic Acid / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D002874:Chromosome Mapping; D017931:DNA Primers; D004351:Drug Resistance / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D006540:Herbicides / Q000633:toxicity; D040582:Inheritance Patterns / Q000235:genetics; D008190:Lyases / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009579:Nitrobenzoates / Q000633:toxicity; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000037:antagonists & inhibitors; D010858:Pigmentation / Q000235:genetics; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism; D050768:Protoporphyrinogen Oxidase; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D045725:Tetrapyrroles / Q000096:biosynthesis*
chemical_list: D017931:DNA Primers; D006540:Herbicides; D009579:Nitrobenzoates; D021122:Protein Subunits; D045725:Tetrapyrroles; D000622:Aminolevulinic Acid; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050768:Protoporphyrinogen Oxidase; D008190:Lyases; C086788:magnesium chelatase; C018425:acifluorfen