Detoxification of the phytoalexin pisatin by a fungal cytochrome P-450

Matthews, David E.; Etten, H. D. Van

doi:10.1016/0003-9861(83)90237-0

Cited by 78 publications

(51 citation statements)

References 40 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…R. fascians might have evolved this specialized system to fulfill the specific oxygen demands in the bacteria during the infection. P-450 monooxygenases were found in other microorganisms interacting with plants (e.g., pisatin demethylase in Nectria haematococca and pinF in octopine-type Agrobacterium tumefaciens strains [23,28]). The role of Nectria pisatin demethylase in degrading phytoalexins of the plant host, allowing infection by the fungus, has been clearly demonstrated (24).…”

Section: Figmentioning

confidence: 99%

The fas operon of Rhodococcus fascians encodes new genes required for efficient fasciation of host plants

et al. 1994

View full text Add to dashboard Cite

Three virulence loci (fas, ftt, and hyp) of Rhodococcus fascians D188 have been identified on a 200-kb conjugative linear plasmid (pFiD188). The fas locus was delimited to a 6.5-kb DNA fragment by insertion mutagenesis, single homologous disruptive recombination, and in trans complementation of different avirulent insertion mutants. The locus is arranged as a large operon containing six open reading frames whose expression is specifically induced during the interaction with host plants. One predicted protein is homologous to P-450 cytochromes from actinomycetes. The putative ferredoxin component is of a novel type containing additional domains homologous to transketolases from chemoautotrophic, photosynthetic, and methylotrophic microorganisms. Genetic analysis revealed thatfas encodes, in addition to the previously identified ipt, at least two new genes that are involved in fasciation development, one of which is only required on older tobacco plants.The interaction between Rhodococcus fascians and host plants leads to the loss of apical dominance and the development of multiple malformed shoots at the site of infection (fasciation). This proliferation is governed by multiple bacterial loci located both on a linear Fi plasmid and on the chromosome (reference 8 and unpublished results). From the three identified loci on pFiD188, only inactivation of one (fas) leads to a complete loss of phytopathogenicity. In this locus, an open reading frame (ORF) coding for an isopentenyltransferase (ipt) has been identified by sequence homology to other cytokinin biosynthesis genes and by biochemical approaches (8). Expression of ipt in R. fascians is regulated by an inducing factor which can only be detected in significant amounts in extracts from tumor tissues (induced by R. fascians) (8).In this paper, we present genetic data that allowed the definition of the fas locus on a 6.5-kb DNA fragment whose complete nucleotide sequence was determined. Six ORFs directed in the same orientation as the previously defined ipt were identified. ORFi and the amino-terminal part of ORF2 have extensive homologies, to P-450 cytochromes and ferredoxins from actinomycetes, whereas the carboxy-terminal portion of ORF2 has conserved regions homologous to the aminoterminal part of transketolases from chemoautotrophic, photosynthetic, or methylotrophic microorganisms.The isolation of new fas mutants and complementation analysis revealed that fas encodes new genes involved in fasciation of the host plant.MATERIALS AND METHODS Bacterial strains and plasmids. Growth conditions and antibiotic concentrations for R. fascians strains have been described previously (11). The Escherichia coli strains used for

show abstract

Section: Figmentioning

confidence: 99%

The fas operon of Rhodococcus fascians encodes new genes required for efficient fasciation of host plants

et al. 1994

View full text Add to dashboard Cite

show abstract

“…Pisatin is demethylated by a Cyt P-450 monooxygenase (16). Phaseollin is hydroxylated to la-hydroxyphaseollone by a reaction which also appears to be oxygenase-mediated, since 180 labeling has shown that the new oxygen atom is derived from 02 (15).…”

mentioning

confidence: 99%

Role of Oxygenases in Pisatin Biosynthesis and in the Fungal Degradation of Maackiain

Matthews¹,

Weiner²,

Matthews³

et al. 1987

Plant Physiol.

Self Cite

View full text Add to dashboard Cite

Some isolates of the plant pathogen Nectria haematococca detoxify the isoflavonoid phytoalexin (-)maackiain by hydroxylation at carbon 6a. Precursor feeding studies strongly suggest that the penultimate step in (+)pisatin biosynthesis by Pisum sativum is 6a-hydroxylation of (+)maackiain. We have used "O labeling to test the involvement of oxygenases in these two reactions. When fungal metabolism of maackiain took place under '"02, the product was labeled with 99% efficiency; no label was incorporated by metabolism in H210. Pisatin synthesized by pea pods in the presence of 1802 or H2180 was a mixture of molecules containing up to three labeled oxygen atoms. Primary mass spectra of such mixtures were complex but were greatly simplified by tandem MS. This analysis indicated that the 6a oxygen of pisatin was derived from H20 and not from 02. Labeling patterns for the other five oxygen atoms were consistent with the proposed pathway for biosynthesis of pisatin and related isoflavonoids. We conclude that the fungal hydroxylation of maackiain is catalyzed by an oxygenase, but the biosynthetic route to the 6a hydroxyl of pisatin is unknown.Several pterocarpan phytoalexins are known to be detoxified by Nectria haematococca or by related fungi with the same imperfect state, Fusarium solani. Pisatin is demethylated by a Cyt P-450 monooxygenase (16). Phaseollin is hydroxylated to la-hydroxyphaseollone by a reaction which also appears to be oxygenase-mediated, since 180 labeling has shown that the new oxygen atom is derived from 02 (15). Maackiain and medicarpin are metabolized by one or more of three different initial reactions, depending on the fungal isolate; all three involve the net addition of one oxygen atom (I1, 12). One of these reactions produces the la-hydroxydienone analogous to the phaseollin metabolite. Another, the hydroxylation at carbon 6a, also involves incorporation of an atom from 02, as reported below.Oxygenases are also thought to be responsible for several reactions in the biosynthesis of these phytoalexins. In particular, the 6a-hydroxylation of maackiain has been proposed to be a step in pisatin biosynthesis by Pisum sativum (Fig. 1) (2-4). This reaction is not identical with the fungal conversion, since the fungus metabolized only (-)maackiain (23) whereas the expected precursor of (+)pisatin, the isomer normally produced by pea, would be the enantiomer (+)maackiain. larity between these two reactions, which appear to play such opposed roles in the interaction between host and parasite, prompted us to examine both of them in this study.MATERIALS AND METHODS Biological Materials. Nectria haematococca Berk. and Br. mating population VI isolate T-95, from our culture collection (22, 23), was maintained on V-8 juice agar and grown in glucoseasparagine (GA) liquid medium as described (25). Pisum sativum L. cultivar Alaska was grown in a greenhouse.6a-Hydroxylation of Maackiain. A 3-d culture of N. haematococca in GA medium was filtered, weighed, and suspended in double strength GA medium at 60 m...

show abstract

“…ochraceus. However, other investigators have shown that cyanide does not significantly affect enzymic activity in cellfree preparations of the fungal system (Ferris et at., 1976;Ghosh et al, 1983;Matthews & van Etten, 1983). The activity of hepatic cytochrome P-450 is widely thought to be insensitive to cyanide (Omura & Sato, 1967).…”

Section: Discussionmentioning

confidence: 99%

Degradation of Aflatoxin by Aspergillus flavus

Hamid

Smith²

1987

Microbiology

View full text Add to dashboard Cite

2023Aflatoxin degradative activity was demonstrated in 6-to 12-d-old intact mycelium and cell-free extracts of Aspergillus Jlauus. The addition of cycloheximide, SKF 525-A or metyrapone to cultures of A . Jlavus prevented subsequent degradation of the aflatoxins, while in cell-free extracts degradation was inhibited by SKF 525-A, metyrapone and cytochrome c but not by KCN. In cell-free extracts, aflatoxin degradation was enhanced by NADPH and NaIO,. The results suggest the involvement of cytochrome P-450 monooxygenases in the aflatoxin degradative activity of A. flaws.

show abstract

Detoxification of the phytoalexin pisatin by a fungal cytochrome P-450

Cited by 78 publications

References 40 publications

The fas operon of Rhodococcus fascians encodes new genes required for efficient fasciation of host plants

The fas operon of Rhodococcus fascians encodes new genes required for efficient fasciation of host plants

Role of Oxygenases in Pisatin Biosynthesis and in the Fungal Degradation of Maackiain

Degradation of Aflatoxin by Aspergillus flavus

Contact Info

Product

Resources

About