Identification and expression analysis of <it>WRKY </it>transcription factor genes in canola <it>(Brassica napus </it>L.) in response to fungal pathogens and hormone treatments

<p>Abstract</p> <p>Background</p> <p>Members of plant WRKY transcription factor families are widely implicated in defense responses and various other physiological processes. For canola (<it>Brassica napus </it>L.), no WRKY genes have been described in detail. Because of the economic importance of this crop, and its evolutionary relationship to <it>Arabidopsis thaliana</it>, we sought to characterize a subset of canola <it>WRKY </it>genes in the context of pathogen and hormone responses.</p> <p>Results</p> <p>In this study, we identified 46 <it>WRKY </it>genes from canola by mining the expressed sequence tag (EST) database and cloned cDNA sequences of 38 <it>BnWRKY</it>s. A phylogenetic tree was constructed using the conserved WRKY domain amino acid sequences, which demonstrated that BnWRKYs can be divided into three major groups. We further compared <it>BnWRKYs </it>to the 72 <it>WRKY </it>genes from <it>Arabidopsis </it>and 91 <it>WRKY </it>from rice, and we identified 46 presumptive orthologs of <it>AtWRKY </it>genes. We examined the subcellular localization of four BnWRKY proteins using green fluorescent protein (GFP) and we observed the fluorescent green signals in the nucleus only.</p> <p>The responses of 16 selected <it>BnWRKY </it>genes to two fungal pathogens, <it>Sclerotinia sclerotiorum </it>and <it>Alternaria brassicae</it>, were analyzed by quantitative real time-PCR (qRT-PCR). Transcript abundance of 13 <it>BnWRKY </it>genes changed significantly following pathogen challenge: transcripts of 10 <it>WRKY</it>s increased in abundance, two <it>WRKY </it>transcripts decreased after infection, and one decreased at 12 h post-infection but increased later on (72 h). We also observed that transcript abundance of 13/16 <it>BnWRKY </it>genes was responsive to one or more hormones, including abscisic acid (ABA), and cytokinin (6-benzylaminopurine, BAP) and the defense signaling molecules jasmonic acid (JA), salicylic acid (SA), and ethylene (ET). We compared these transcript expression patterns to those previously described for presumptive orthologs of these genes in <it>Arabidopsis </it>and rice, and observed both similarities and differences in expression patterns.</p> <p>Conclusion</p> <p>We identified a set of 13 <it>BnWRKY </it>genes from among 16 <it>BnWRKY </it>genes assayed, that are responsive to both fungal pathogens and hormone treatments, suggesting shared signaling mechanisms for these responses. This study suggests that a large number of BnWRKY proteins are involved in the transcriptional regulation of defense-related genes in response to fungal pathogens and hormone stimuli.</p>