Expression analysis of <i>WRKY</i> genes from <i>Poncirus trifoliata</i> in response to pathogen infection

<div><p>The majority of WRKY transcription factors (TFs) play a role in the regulation of defense response in plants. Three <i>WRKY</i> genes, <i>PtrWRKY1, PtrWRKY2 and PtrWRKY3</i>, were previously identified in <i>Poncirus</i> and their expressions were characterized in response to cold and drought in <i>Poncirus</i> and <i>Citrus</i>. In this study, expressions of these <i>WRKY</i> genes were studied in response to infection with two major pathogens of <i>Citrus</i>, <i>Citrus tristeza virus</i> (CTV) and <i>Phytophthora citrophthora</i>, in resistant <i>Poncirus</i> and susceptible pummelo (<i>Citrus grandis</i>) plants. Northern blot analysis showed that the expression of the <i>PtrWRKY1</i> gene was induced earlier and stronger in <i>Poncirus</i> than in pummelo in response to CTV infection. On the other hand, the expression of the <i>PtrWRKY1</i> gene was not altered in response to <i>P. citrophthora</i> infection neither in <i>Poncirus</i> nor in pummelo. When the expression of the <i>PtrWRKY2</i> gene was analyzed, it was repressed by CTV inoculation in <i>Poncirus</i> plants, whereas the expression was not changed in response to CTV infection in pummelo or in response to <i>P. citrophthora</i> inoculation in <i>Poncirus</i> or pummelo. Similarly, the expression of the <i>PtrWRKY3</i> gene was repressed in <i>Poncirus</i>, but not changed in pummelo by CTV inoculation; however, the expression of the <i>PtrWRKY3</i> gene was induced in <i>Poncirus</i>, but it was repressed in pummelo in response to <i>P. citrophthora</i> inoculation. The expression analysis of three different <i>WRKY</i> genes revealed that they are differentially expressed in response to CTV and <i>P. citrophthora</i> infection in resistant <i>Poncirus</i> and susceptible pummelo suggesting that they may play a role in disease resistance in <i>Poncirus</i>.</p></div>