Arabidopsis PAD3, a gene required for camalexin biosynthesis, encodes a putative cytochrome P450 monooxygenase.
Phytoalexins are low molecular weight antimicrobial compounds that are synthesized in response to pathogen attack. The phytoalexin camalexin, an indole derivative, is produced by Arabidopsis in response to infection with the bacterial pathogen Pseudomonas syringae. The phytoalexin deficient 3 (pad3) mutation, which causes a defect in camalexin production, has no effect on resistance to P. syringae but compromises resistance to the fungal pathogen Alternaria brassicicola. We have now isolated PAD3 by map-based cloning. The predicted PAD3 protein appears to be a cytochrome P450 monooxygenase, similar to those from maize that catalyze synthesis of the indole-derived secondary metabolite 2,4-dihydroxy-1, 4-benzoxazin-3-one. The expression of PAD3 is tightly correlated with camalexin synthesis and is regulated by PAD4 and PAD1. On the basis of these findings, we conclude that PAD3 almost certainly encodes an enzyme required for camalexin biosynthesis. Moreover, these results strongly support the idea that camalexin does not play a major role in plant resistance to P. syringae infection, although it is involved in resistance to a fungal pathogen.
Zhou
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Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA.
Tootle
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Glazebrook
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D016960:Agrobacterium tumefaciens / Q000235:genetics; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics* / Q000382:microbiology; D029681:Arabidopsis Proteins; D001483:Base Sequence; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007113:Immunity, Innate; D007211:Indoles / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010936:Plant Extracts / Q000235:genetics; D018515:Plant Leaves / Q000201:enzymology; D011549:Pseudomonas / Q000472:pathogenicity; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012717:Sesquiterpenes; D013729:Terpenes; D013844:Thiazoles / Q000378:metabolism*; D000094162:Phytoalexins
D000900:Anti-Bacterial Agents; D029681:Arabidopsis Proteins; D007211:Indoles; D010936:Plant Extracts; D012717:Sesquiterpenes; D013729:Terpenes; D013844:Thiazoles; C102405:camalexin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C417307:PAD3 protein, Arabidopsis; D000094162:Phytoalexins