The Clubroot Pathogen (Plasmodiophora brassicae) Influences Auxin Signaling to Regulate Auxin Homeostasis in Arabidopsis

Abstract

The clubroot disease, caused by the obligate biotrophic protist Plasmodiophora brassicae, affects cruciferous crops worldwide. It is characterized by root swellings as symptoms, which are dependent on the alteration of auxin and cytokinin metabolism. Here, we describe that two different classes of auxin receptors, the TIR family and the auxin binding protein 1 (ABP1) in Arabidopsis thaliana are transcriptionally upregulated upon gall formation. Mutations in the TIR family resulted in more susceptible reactions to the root pathogen. As target genes for the different pathways we have investigated the transcriptional regulation of selected transcriptional repressors (Aux/IAA) and transcription factors (ARF). As the TIR pathway controls auxin homeostasis via the upregulation of some auxin conjugate synthetases (GH3), the expression of selected GH3 genes was also investigated, showing in most cases upregulation. A double gh3 mutant showed also slightly higher susceptibility to P. brassicae infection, while all tested single mutants did not show any alteration in the clubroot phenotype. As targets for the ABP1-induced cell elongation the effect of potassium channel blockers on clubroot formation was investigated. Treatment with tetraethylammonium (TEA) resulted in less severe clubroot symptoms. This research provides evidence for the involvement of two auxin signaling pathways in Arabidopsis needed for the establishment of the root galls by P. brassicae.

Type III Secretion–Dependent and –Independent Phenotypes Caused by Ralstonia solanacearum in Arabidopsis Roots

“…For instance, root hairs are the entry point of both mutualistic rhizobacteria (Rodríguez-Navarro et al 2007) and pathogenic bacteria such as Plasmodiophora brassicaceae, the causal agent of clubroot disease (Kageyama and Asano 2009). Interestingly, auxin signaling was proposed to promote cell-wall remodeling to allow root-hair growth (Breakspear et al 2014) and it has been shown to be a key component of both pathogenic and mutualistic root-hair infections (Jahn et al 2013;Laplaze et al 2015).…”

Auxin homeostasis, signaling, and interaction with other growth hormones during the clubroot disease of Brassicaceae

“…2 The GH3 proteins conjugate various substrates (i.e., IAA and other auxins, as well as jasmonic, salicylic, and benzoic acids) to a broad spectrum of amino acids.…”

“…6 Jahn et al 2 found that genes encoding the auxin conjugating enzymes, which are partially also auxin inducible, 7 were upregulated during the clubroot disease. Extracting data for GH3 gene expression from a recently published cell-type specific microarray 8 corroborated these results (Fig.…”

“…While single mutants of gh3.5 did not show any altered clubroot phenotype, double mutants in gh3.5gh3.17 were more susceptible to the parasite. 2 To find other players involved in GH3.5. function an association map 12 was constructed for GH3.5 ( Fig.…”

“…the samples were from roots 14 and 21 d after inoculation and included small (SP) and large plasmodia (LP)-containing cells. the 2 GH3 genes investigated in more detail in Jahn et al 2 are highlighted in red. the cartoons indicate the respective cell type.…”