Investigation of the Roles of Phosphatidylinositol 4-Phosphate 5-Kinases 7,9 and Wall-Associated Kinases 1–3 in Responses to Indole-3-Carbinol and Biotic Stress in Arabidopsis Thaliana

Indole-3-carbinol (I3C), a hydrolysis product of indole-3-methylglucosinolate, is toxic to herbivorous insects and pathogens. In mammals, I3C is extensively studied for its properties in cancer prevention and treatment. Produced in Brassicaceae, I3C reversibly inhibits root elongation in a concentration-dependent manner. This inhibition is partially explained by the antagonistic action of I3C on auxin signaling through TIR1. To further elucidate the mode of action of I3C in plants, we have employed a forward-genetic amiRNA screen that circumvents functional redundancy. We identified and characterized two amiRNA lines with impaired I3C response. The first line, ICT2, targets the phosphatidylinositol 4-phosphate 5-kinase family (PIP5K), exhibiting tolerance to I3C, while the second line, ICS1, targets the Wall-Associated Kinases (WAK1–3) family, showing susceptibility to I3C. Both lines maintain I3C-induced antagonism of auxin signaling, indicating that their phenotypes are due to auxin-independent mechanisms. Transcript profiling experiments reveal that both lines are transcriptionally primed to respond to I3C treatment. Physiological, metabolomic, and transcriptomic analysis reveal that these kinases mediate numerous developmental processes and are involved in abiotic and biotic stress responses.