WRKY33 binding sites in Arabidopsis upon Botrytis cinerea 2100 inoculation. Arabidopsis thaliana

The Arabidopsis thaliana mutant wrky33 is highly susceptible to the necrotrophic fungus Botrytis cinerea. We identified by ChIP-seq >1680 high-confidence WRKY33 binding sites associated with 1576 genes within the Arabidopsis genome, with all of them being dependent on rapid activation of WRKY33 expression by Botrytis cinerea strain 2100. Genome-wide transcriptional analysis defined 318 genes as direct functional targets at 14 h post inoculation. Comparison between resistant wild-type Columbia-0 and susceptible wrky33 mutant plants revealed that expression of 75% of all WRKY33 regulated targets were down-regulated upon infection, indicating that WRKY33 predominately acts as a repressor. However, WRKY33 appears to possess dual functionality acting either as a repressor or as an activator in a promoter-context dependent manner. Our genome-wide analysis confirmed known WRKY33 targets involved in ethylene and jasmonic acid hormone signaling and phytoalexin biosynthesis, but also uncovered a previously unknown role of abscisic acid (ABA) biosynthesis in the complex regulatory circuitry affecting resistance towards Botrytis. Overall design: Analysis of transgenic plants expressing WRKY33-HA under its native promoter post inoculation with spores of Botrytis cinerea 2100