Abstract
The Arabidopsis mutant wrky33 is highly susceptible to Botrytis cinerea. We identified >1680 Botrytis-induced WRKY33 binding sites associated with 1576 Arabidopsis genes. Transcriptional profiling defined 318 functional direct target genes at 14 hr post inoculation. Comparative analyses revealed that WRKY33 possesses dual functionality acting either as a repressor or as an activator in a promoter-context dependent manner. We confirmed known WRKY33 targets involved in hormone signaling and phytoalexin biosynthesis, but also uncovered a novel negative role of abscisic acid (ABA) in resistance towards B. cinerea 2100. The ABA biosynthesis genes NCED3 and NCED5 were identified as direct targets required for WRKY33-mediated resistance. Loss-of-WRKY33 function resulted in elevated ABA levels and genetic studies confirmed that WRKY33 acts upstream of NCED3/NCED5 to negatively regulate ABA biosynthesis. This study provides the first detailed view of the genome-wide contribution of a specific plant transcription factor in modulating the transcriptional network associated with plant immunity.
Highlights
Necrotrophic fungi including Botrytis cinerea, Fusarium oxysporum, and Alternaria brassicicola, are the largest class of fungal phytopathogens causing serious crop losses worldwide (Łaźniewska et al, 2010)
MKS1 thereby releasing WRKY33 from the complex and leading to its detection at the PAD3 promoter. 106 We previously reported that activation of Arabidopsis WRKY33 resulted in rapid and massive host transcriptional reprogramming upon infection with B. cinerea strain 2100 (Birkenbihl et al, 2012)
We identified 1684 high confidence WRKY33 binding sites common to both replicates, which are associated with 1576 genes (Figure 2C, Supplementary file 1)
Summary
Necrotrophic fungi including Botrytis cinerea, Fusarium oxysporum, and Alternaria brassicicola, are the largest class of fungal phytopathogens causing serious crop losses worldwide (Łaźniewska et al, 2010) These pathogens extract nutrients from dead host cells by producing a variety of phytotoxic compounds and cell wall degrading enzymes (Mengiste, 2012; Williamson et al., 2007). Transgenic Arabidopsis lines over-expressing ERF1 or ORA59 confer resistance to B. cinerea (Kazan and Manners, 2013) whereas RNAi-ORA59 silenced lines were more susceptible (Berrocal-Lobo et al, 2002; Pré et al, 2008) Both ERF1 and ORA59 appear to be key integrators of the ET- and JA-signaling pathways (Pieterse et al, 2009). Upon challenge with the hemibiotrophic pathogen Pseudomonas syringae or upon elicitation by the Microbe-Associated Molecular Pattern (MAMP) flg, the active epitope of the bacterial flagella, activated MPK4 phosphorylates
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