The biosynthesis of camalexin, the main phytoalexin of the model plant Arabidopsis thaliana, involves at least two CYP (cytochrome P450) steps. It is synthesized from tryptophan via indole-3-acetaldoxime in a reaction catalysed by CYP79B2 and CYP79B3. Based on the pad3 mutant phenotype, CYP71B15 (PAD3) had also been suggested as a camalexin biosynthetic gene. CYP71B15 catalyses the final step in camalexin biosynthesis, as recombinant CYP71B15 and microsomes from Arabidopsis leaves expressing functional PAD3 converted dihydrocamalexic acid into camalexin. The biosynthetic pathway is co-ordinately induced, strictly localized to the site of pathogen infection. This provides a model system to study the regulation of CYP enzymes involved in phytoalexin biosynthesis.

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