Abstract
Clubroot disease is a serious threat to canola production in western Canada and many parts of the world. Rcr1 is a clubroot resistance (CR) gene identified recently and its molecular mechanisms in mediating CR have been studied using several omics approaches. The current study aimed to characterize the biochemical changes in the cell wall of canola roots connecting to key molecular mechanisms of this CR gene identified in prior studies using Fourier transform infrared (FTIR) spectroscopy. The expression of nine genes involved in phenylpropanoid metabolism was also studied using qPCR. Between susceptible (S) and resistance (R) samples, the most notable biochemical changes were related to an increased biosynthesis of lignin and phenolics. These results were supported by the transcription data on higher expression of BrPAL1. The up-regulation of PAL is indicative of an inducible defence response conferred by Rcr1; the activation of this basal defence gene via the phenylpropanoid pathway may contribute to clubroot resistance conferred by Rcr1. The data indicate that several cell-wall components, including lignin and pectin, may play a role in defence responses against clubroot. Principal components analysis of FTIR data separated non-inoculated samples from inoculated samples, but not so much between inoculated S and inoculated R samples. It is also shown that FTIR spectroscopy can be a useful tool in studying plant-pathogen interaction at cellular levels.
Highlights
Clubroot, caused by the obligate soil-borne pathogen Plasmodiophora brassicae Woronin, is a serious disease of Brassica crops worldwide [1] and a threat to canola (Brassica napus L.) production in western Canada [2]
The objective of this study was to assess the potential of using Fourier transform infrared (FTIR) spectroscopy with quantitative PCR to identify biochemical and molecular traits associated with the clubroot resistance mediated by Rcr1, especially in relation to changes in cell wall components during the infection by P. brassicae, as suggested by the transcriptome study earlier [11]
The P. brassicae inoculation caused substantial changes in the spectra of resistant (R) and susceptible (S) roots when compared to respective controls; the characteristic spectral peaks that can be assigned to distinct functional groups are presented in Table 1 and Figure 1
Summary
Clubroot, caused by the obligate soil-borne pathogen Plasmodiophora brassicae Woronin, is a serious disease of Brassica crops worldwide [1] and a threat to canola (Brassica napus L.) production in western Canada [2]. Clubroot resistance (CR) has been found from only limited sources, mainly B. rapa ssp. Eight CR loci have been mapped to five B. rapa linkage groups [7,8,9,10], but the resistance mechanisms are generally unclear for most of these CR genes [11]. Some of the CR genes were incorporated into B. napus oilseed rape first in Europe; “Mendel” and “Tosca” were registered in 2000s [12], with each cultivar receiving one race-specific CR genes from a turnip cultivar. CR genes have been incorporated into rutabaga Further work characterized the CR gene Rcr in B. rapa ssp.
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