Overexpression of BnWRKY33 in oilseed rape enhances resistance to S clerotinia sclerotiorum

Summary S clerotinia sclerotiorum causes a devastating disease in oilseed rape ( B rassica napus ) resulting in a tremendous yield loss worldwide. Studies on various host–pathogen interactions have shown that plant WRKY transcription factors are essential for defence. For the B . napus – S . sclerotiorum interaction, little direct evidence has been found with regard to the biological roles of specific WRKY genes in host resistance. In this study, we isolated a B . napus WRKY gene, BnWRKY33 , and found that the gene is highly responsive to S . sclerotiorum infection. Transgenic B . napus plants overexpressing BnWRKY33 showed markedly enhanced resistance to S . sclerotiorum , constitutive activation of the expression of BnPR1 and BnPDF1 .2 , and inhibition of H 2 O 2 accumulation in response to pathogen infection. Further, we isolated a mitogen‐activated protein ( MAP ) kinase substrate gene, BnMKS1 , and found that not only can BnWRKY33 interact with BnMKS1 , which can also interact with BnMPK4 , using the yeast two‐hybrid assay, consistent with their collective nuclear localization, but also BnWRKY33 , BnMKS1 and BnMPK4 are substantially and synergistically expressed in response to S . sclerotiorum infection. In contrast, the three genes showed differential expression in response to phytohormone treatments. Together, these results suggest that BnWRKY33 plays an important role in B . napus defence to S . sclerotiorum , which is most probably associated with the activation of the salicylic acid ( SA )‐ and jasmonic acid ( JA )‐mediated defence response and inhibition of H 2 O 2 accumulation, and we propose a potential mechanism in which BnMPK4 – BnMKS1 – BnWRKY33 exist in a nuclear localized complex to regulate resistance to S . sclerotiorum in oilseed rape.