Camalexin contributes to the partial resistance of Arabidopsis thaliana to the biotrophic soilborne protist Plasmodiophora brassicae

Abstract

Camalexin has been reported to play defensive functions against several pathogens in Arabidopsis. In this study, we investigated the possible role of camalexin accumulation in two Arabidopsis genotypes with different levels of basal resistance to the compatible eH strain of the clubroot agent Plasmodiophora brassicae. Camalexin biosynthesis was induced in infected roots of both Col-0 (susceptible) and Bur-0 (partially resistant) accessions during the secondary phase of infection. However, the level of accumulation was four-to-seven times higher in Bur-0 than Col-0. This was associated with the enhanced transcription of a set of camalexin biosynthetic P450 genes in Bur-0: CYP71A13, CYP71A12, and CYP79B2. This induction correlated with slower P. brassicae growth in Bur-0 compared to Col-0, thus suggesting a relationship between the levels of camalexin biosynthesis and the different levels of resistance. Clubroot-triggered biosynthesis of camalexin may also participate in basal defense in Col-0, as gall symptoms and pathogen development were enhanced in the pad3 mutant (Col-0 genetic background), which is defective in camalexin biosynthesis. Clubroot and camalexin responses were then studied in Heterogeneous Inbred Families (HIF) lines derived from a cross between Bur-0 and Col-0. The Bur/Col allelic substitution in the region of the previously identified clubroot resistance QTL PbAt5.2 (Chromosome 5) was associated with both the enhanced clubroot-triggered induction of camalexin biosynthesis and the reduced P. brassicae development. Altogether, our results suggest that high levels of clubroot-triggered camalexin biosynthesis play a role in the quantitative control of partial resistance of Arabidopsis to clubroot.

Genetic Components of Root Architecture Remodeling in Response to Salt Stress

“…The IAOx pathway is Brassica specific and can produce three types of active compounds: camalexin, indole glucosinolates, and indole-3-acetic acid (Hull et al, 2000;Zhao et al, 2002;Mikkelsen et al, 2000;Glawischnig et al, 2004;Sugawara et al, 2009). Both camalexin and indole glucosinolates act as defense compounds induced in both shoot and root upon pathogen attack (Glawischnig, 2007;Halkier and Gershenzon, 2006;Brown et al, 2003;Lemarié et al, 2015), but no clear link to root development has been found. The IAOx pathway has been shown to contribute to auxin production under heat stress conditions (Zhao et al, 2002).…”

Translational Regulation of Metabolic Dynamics during Effector-Triggered Immunity

“…Interestingly, the reduction in tryptophan is contrary to the upregulation of genes within the tryptophan biosynthetic pathway (Figure 4). The observed decrease in the tryptophan level may be due to a potential increase in the biosynthesis of the tryptophan-derived antimicrobial phytoalexin, camalexin (Lemarié et al, 2015), through the dramatic increases in both RS and RF (66-fold) of the key camalexin biosynthetic enzyme, tryptophan N-monooxygenase, CYP79B2 (EC 1.14.14.156; Figure 4 and Supplemental Figure 7A). Moreover, the CYP79B2 mRNA had a slight increase of ribosomal association upon ETI induction in the ribosome pelleting experiment, suggesting a potential contribution of translational regulation (Supplemental Figure 7B).…”

The formation of a camalexin-biosynthetic metabolon

“…Phosphinothricin-resistant primary transformants were confirmed by PCR and qualitatively screened for GFP fluorescence in response to AgNO 3 spraying. A high-expression line was crossed to the cyp71b15/pad3 T-DNA insertion line SALK_026585 (Xu et al, 2008;Lemarié et al, 2015), and homozygous pad3/CYP71B15 pro :CYP71B15-GFP plants that carried the construct and (at least partially) complemented the camalexin-deficient pad3 phenotype were selected from the F2 generation (Supplemental Figure 1B). The progeny of one individual was used for proteomics analysis.…”