Pseudomonas syringaeinfectivity correlates to altered transcript and metabolite levels ofArabidopsisMediator mutants

Abstract

ABSTRACTRapid metabolic responses to pathogens are essential for plant survival and depend on numerous transcription factors. Mediator is the major transcriptional co-regulator for integration and transmission of signals from transcriptional regulators to RNA polymerase II. Using four Arabidopsis Mediator mutants,med16,med18,med25andcdk8, we studied how differences in regulation of their transcript and metabolite levels correlate to their responses toPseudomonas syringaeinfection. We found thatmed16andcdk8were susceptible, whilemed25showed increased resistance. Glucosinolate, phytoalexin and carbohydrate levels were reduced already before infection inmed16andcdk8, but increased inmed25, which also displayed increased benzenoids levels. Early after infection, wild type plants showed reduced glucosinolate and nucleoside levels, but increases in amino acids, benzenoids, oxylipins and the phytoalexin Camalexin. The Mediator mutants showed altered levels of these metabolites and in regulation of genes encoding key enzymes for their metabolism. At later stage, mutants displayed defective levels of specific amino acids, carbohydrates, lipids and jasmonates which correlated to their infection response phenotypes. Our results reveal thatMED16,MED25andCDK8are required for a proper, coordinated transcriptional response of genes which encode enzymes involved in important metabolic pathways for Arabidopsis responses toPseudomonas syringaeinfections.HIGHLIGHTPlants need to defend themselves against different types of infections. We show that subunits of the Mediator transcriptional coactivator coordinate metabolic responses ofArabidopsis thalianato infections byPseudomonas syringae.