Inducible expression of a Nep1-like protein serves as a model trigger system of camalexin biosynthesis

Camalexin, the major Arabidopsis phytoalexin, is synthesized in response to a great variety of pathogens. Specific pathogen-associated molecular patterns, such as Nep1-like proteins from oomycetes act as signals triggering the transcriptional activation of the camalexin biosynthetic genes. PaNie, a Nep1-like protein from Pythium aphanidermatum was expressed in Arabidopsis under the control of an ethanol-inducible promoter. This system was developed as a tool to study the regulation of camalexin biosynthesis. It allowed induction of camalexin preceded by strong transcriptional activation of the tryptophan and camalexin biosynthetic genes. In flowers and green siliques PaNie expression elicited only minor camalexin formation, indicating low capability for phytoalexin synthesis in reproductive organs in contrast to leaf and stem tissue.