PAD3

PAD3, short for phytoalexin deficient 3, is a gene in the model plant Arabidopsis thaliana. It encodes a cytochrome P450 monooxygenase, commonly referred to as CYP71B15, that plays a key role in the biosynthesis of camalexin, the plant’s main indole-derived phytoalexin.

Function and biosynthesis: PAD3 acts in the late steps of camalexin production, catalyzing a conversion essential for forming camalexin from its intermediate dihydrocamalexic acid. Camalexin is produced by Arabidopsis in response to pathogen attack and other stress, contributing to the plant’s chemical defense arsenal.

Regulation and expression: PAD3 expression is induced by pathogen challenge and stress signaling. Its activity is coordinated with other defense components and regulatory pathways that control phytoalexin production, including signaling networks involving salicylic acid and other defense responses.

Mutant phenotypes and significance: Loss-of-function pad3 mutants show greatly reduced or undetectable camalexin accumulation and often exhibit altered resistance to certain pathogens, underscoring PAD3’s importance in defense. As part of the camalexin biosynthetic pathway, PAD3 intersects with broader defense regulation in Arabidopsis, including interactions with other PAD genes and EDS1/PAD4-related signaling.

Context and use: PAD3 is a widely studied gene in plant-pathogen interaction research. Its sequence, expression patterns, and mutant phenotypes provide insights into phytoalexin biosynthesis and the coordination of chemical defenses with immune signaling in plants. See also camalexin, PAD4, and related defense pathways.