WRKY transcription factors involved in salicylic acid-induced defense gene expression

Abstract

The salicylic acid (SA) signaling pathway triggered by attack of biotrophic pathogens leads to broad spectrum resistance against a plethora of pathogenic fungi, bacteria and viruses and is known as systemic acquired resistance (SAR). One of the hallmarks of SAR is the accumulation of PR proteins and the induced expression of the PR-1 gene is often used as a marker for SAR. In this thesis we describe the characterization of a WRKY-class transcription factor (NtWRKY12) that specifically binds to the sequence TTTTCCAC. This sequence differs significantly from the consensus WRKY protein binding site TTGAC[C/T] (W-box), and was designated as the __WK-box__. The activation of PR-1a has always been proposed to occur mainly via TGA-factors. We show that NtWRKY12 can bind to TGA2.2 and has a more essential role in PR-1a activation. Using bioinformatic analysis various candidate genes have been prospected to have a role in regulation of the SA, jasmonate (JA) and ethylene (ET) biosynthesis or signaling pathways. The connection between AtWRKY28 and ICS1 was further studied. In protoplasts AtWRKY28 can activate ICS1 promoter::GUS reporter constructs and endogenous ICS1 mRNA levels. Using EMSA assays and ChIP experiments the bindingsite has been determined in vitro and confirmed in vivo.