An inducible, nondegradative phytoalexin resistance mechanism in Dictyostelium discoideum is suppressed by mutations that alter membrane sterol composition

Article Abstract:

Inducible resistance to the phytoalexin, pisatin, in Dictyostelium discoideum was examined, and tested for associations with the nystatin resistance genotype. Pretreatment with a sublethal concentration of pisatin resulted in nondegradative pisatin resistance. Mutations in nysC, which confersnystatin resistance, resulted in suppression of pisatin resistance. However, loss of pisatin resistance by transfer to nystatin medium did not result in loss of nystatin resistance. This was explained by a model wherein pisatin resistance is conferred by membrane alterations which are not maintained in theabsence of pisatin.

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Three genes for metabolism of the phytoalexin maackiain in the plant pathogen Nectria haematococca: meiotic instability and relationship to a new gene for pisatin demethylase

Article Abstract:

The genes involved in the metabolism of maackiain (Mak) in Nectria haematococca were identified. Maakiain is an isoflavonoid phytoalexin from chickpea. The genes were identified from crosses between field isolates differing in Mak phenotype. Tetrad analysis showed that two irregularly transmitted genes, Mak1 and Mak2, in strain T-161 converted maakiain to 1a-hydroxymaakiain. Mak1 was closely linked to Pda6, a new gene for pisatin demethylase. A third gene, Mak3, was conventionally inherited and was involved in the conversion of 1a-hydroxymaakiain to 6a-hydroxymaakiain.

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Genetic analysis of the role of phytoalexin detoxification in virulence of the fungus Nectria haematococca on chickpea (Cicer arietinum)

Article Abstract:

The role of phytoalexin detoxification in the virulence interaction of Nectria haematococca on chickpeawas examined. Genetic analysis was facilitated by the recent identification of Mak genes involved in the metabolism of maakiain. The presence of two genes, Mak1 and Mak2, was linked to high virulence on chickpea. The results were inconclusive for a third gene, Mak3, because progeny segregating for this gene were low in virulence. The results suggest that phytoalexin detoxification is required, but insufficient per se, for high levels of virulence.

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