The Beet Cyst Nematode <i>Heterodera schachtii</i> Modulates the Expression of WRKY Transcription Factors in Syncytia to Favour Its Development in Arabidopsis Roots

<div><p>Cyst nematodes invade the roots of their host plants as second stage juveniles and induce a syncytium which is the only source of nutrients throughout their life. A recent transcriptome analysis of syncytia induced by the beet cyst nematode <i>Heterodera schachtii</i> in Arabidopsis roots has shown that thousands of genes are up-regulated or down-regulated in syncytia as compared to root segments from uninfected plants. Among the down-regulated genes are many which code for WRKY transcription factors. Arabidopsis contains 66 <i>WRKY</i> genes with 59 represented by the ATH1 GeneChip. Of these, 28 were significantly down-regulated and 6 up-regulated in syncytia as compared to control root segments. We have studied here the down-regulated genes <i>WRKY6</i>, <i>WRKY11</i>, <i>WRKY17</i> and <i>WRKY33</i> in detail. We confirmed the down-regulation in syncytia with promoter::GUS lines. Using various overexpression lines and mutants it was shown that the down-regulation of these WRKY genes is important for nematode development, probably through interfering with plant defense reactions. In case of <i>WRKY33</i>, this might involve the production of the phytoalexin camalexin.</p>