Differentially expressed genes in canola ( Brassica napus ) during infection by virulent and avirulent Plasmodiophora brassicae pathotypes

Gene expression profiling offers a means of understanding pathogenesis in clubroot of crucifers caused by the biotrophic pathogen Plasmodiophora brassicae. In this study, a canola (Brassica napus) cultivar 45H29 was inoculated with P. brassicae pathotypes 5I (P5I) and 5X (P5X), and the pathogen:plant DNA biomass ratio in roots was determined at 7, 14, and 21 days after inoculation (dai) by quantitative PCR (qPCR) analysis. The P5X:plant biomass ratio increased across the time course, while the P5I:plant biomass ratio decreased. To investigate genes differentially expressed during the infection process, the expression of 205 P. brassicae genes encoding putative secreted proteins was analysed from the inoculated samples at 14 dai. One of the 205 genes was expressed at a higher level in P5X than in P5I, while 15 genes were expressed at a higher level in P5I than in P5X. Of these 16, 13 genes encoded proteins with high cysteine content, while three genes encoded proteins with an RXLR motif. The expression of the 16 genes was analysed further in the 7‐ and 21‐dai samples. No transcripts of the 16 genes were detected from either pathotype at 7 dai. In contrast, 11 genes were differentially expressed between the two pathotypes at 21 dai, with nine being more highly expressed in P5X and two in P5I. One gene showed homology to PbSUNK2 found in P. brassicae‐infected Arabidopsis thaliana root tissues. These 16 genes may offer important information to improve the current understanding of canola–P. brassicae interactions.