Identification and characterization of the genetic factors regulating Indole-3-carbinol activity in Arabidopsis thaliana

Glucosinolates (GLs) are sulfur-and nitrogen-containing secondary metabolites found in the Cruciferae plant family. They are stored as an inactive form in the vacuole until herbivory, or tissue damage, initiate their hydrolysis, resulting in breakdown products toxic to herbivores and pathogens. Indole-3-carbinol (I3C) is one of these breakdown products. In Arabidopsis, exogenously applied I3C inhibits root elongation in a dose-dependent manner, acting as an auxin antagonist that competes for the binding site of the auxin receptor TIR1. Yet, little else is known about I3C perception, signaling and detoxification. We hypothesize that members of protein kinase families are involved in regulating I3C signaling pathways. Using a kinase-targeted forward-genetic amiRNA screen, I identified two kinase families as components involved in the I3C signaling. Indole-3-carbinol resistant 2 (I3CR2), is tolerant to I3C and expresses an amiRNA that targets two members of the phosphatidylinositol phosphate (PIP5K) family. Indole-3-carbinol sensitive 1 (I3CS1) is hyper sensitive to I3C, and targets three members of the wall associated kinase (WAK) family. The tolerance and susceptibility of I3CR2 and I3CS1 respectively, are not specific to I3C where they show similar responses to other chemicals. Genetic and biochemical analyses of the original strains, as well as loss-of-function strains of individual kinases, were carried out. I3CR2 generates less GLs and is more sensitive to Pseudomonas syringae infection compared to WT, while I3CS1 generates more GLs and is more tolerant. These results hint at a role of these kinases families in regulating GLs production, which thus influences sensitivity to biotic stress.