Suppression of clubroot by Heteroconium chaetospira may be mediated by modulation of jasmonic acid pathway signalling. R. LAHLALI, G. PENG, L. MCGREGOR, J. GEISSLER, M. R. MCDONALD, B. D. GOSSEN AND S. F. HWANG. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; (M.R.M.) Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17507 Fort Road N.W., Edmonton, AB T6G 2P5, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin, is a serious threat to canola (Brassica napus L.) production in western Canada. The endophytic fungus Heteroconium chaetospira (Grove) M.B. Ellis (strain B2HB1) is a potential biocontrol agent that reduces clubroot severity in canola by 80% under controlled environment conditions. Internal colonization of canola roots by H. chaetospira was observed using confocal microscopy 2 weeks after treatment. Quantification of root colonization by H. chaetospira and P. brassicae during early infection using qPCR showed that genomic DNA of the two species within the root was strongly and negatively correlated (r 2 = 0.90, P < 0.05). The extent of root colonization by H. chaetospira was also negatively correlated to subsequent clubroot severity. A preliminary profiling of gene expression in canola roots inoculated with H. chaetospira based on a microarray assay identified up-regulation of several defence-related genes, especially those that control the jasmonic acid and ethylene pathways. A biochemical analysis using a mixture reaction assay revealed high activity of phenylalanine ammonia lyases in roots, stems and leaves of inoculated plants; this enzyme catalyzes pathways associated with host defence response. A study using qPCR to quantify transcript levels of two strongly up-regulated defence-related genes identified in the prior microarray assay showed that gene activities encoded for the signal transduction OPR2 (jasmonic acid) and BnSAM3 (ethylene) were enhanced by 4X and 2X, respectively. Taken together, these results indicate that the endophyte H. chaetospira suppresses clubroot via modulation of gene expression that regulates the jasmonic acid and ethylene pathways.