Transcriptional profiling identifies critical steps of cell cycle reprogramming necessary for Plasmodiophora brassicae-driven gall formation in Arabidopsis

Metabolomics and Transcriptomics Reveal the Function of Trigonelline and Its Synthesis Gene BrNANMT in Clubroot Susceptibility of Brassica rapa

Clubroot caused by Plasmodiophora brassicae, a soil-borne pathogen, threatens cruciferous plants, resulting in severe yield reductions. To identify genes and metabolites associated with clubroot resistance and susceptibility, we performed metabolome and transcriptome analyses of Brassica rapa inbred line CRBJN3-2 inoculated with resistant and susceptible P. brassicae strains. Co-expression network analysis revealed that trigonelline accumulation, linked to the nicotinic acid and nicotinamide metabolic pathways, was significantly higher in clubroot-susceptible plants. Furthermore, applying trigonelline externally aggravated clubroot in both B. rapa and Arabidopsis thaliana. Overexpression of the nicotinate N-methyltransferase gene (BrNANMT) responsible for the conversion from nicotinate to trigonelline in these plants increased disease susceptibility, while loss of this gene's function resulted in improved clubroot resistance. Our study is the first to reveal the function of trigonelline in promoting clubroot development and identify BrNANMT as a clubroot susceptibility gene and trigonelline can be used as a marker metabolite in response to P. brassicae infection. Gene editing of BrNANMT provides new insights for the development of Brassica crops with improved resistance to clubroot.

Comprehensive review of Plasmodiophora brassicae: pathogenesis, pathotype diversity, and integrated control methods

Clubroot disease is an important disease of cruciferous crops worldwide caused by Plasmodiophora brassicae. The pathogen P. brassicae can infect almost all cruciferous crops, resulting in a reduction in yield and quality of the host plant. The first part of this review outlines the process of P. brassicae infestation, effectors, physiological pathotypes and identification systems. The latter part highlights and summarizes the various current control measures and research progress on clubroot. Finally, we propose a strategic concept for the sustainable management of clubroot. In conclusion, this paper will help to deepen the knowledge of P. brassicae and the understanding of integrated control measures for clubroot, and to lay a solid foundation for the sustainable management of clubroot.

Local endoreduplication of the host is a conserved process during Phytomyxea-host interaction

Background

Endoreduplication, a modified cell cycle, involves cells duplicating DNA without undergoing mitosis. This phenomenon is frequently observed in plants, algae, and animals. Biotrophic pathogens have been demonstrated to induce endoreduplication in plants to secure more space or nutrients.

Methods

In this study, we investigated the endoreduplication process triggered by two phylogenetically distant Rhizaria organisms-Maullinia spp. (in brown algae) and Plasmodiophora brassicae (in plants)-by combining fluorescent in situ hybridization (FISH) with nuclear area measurements.

Results

We could confirm that Plasmodiophora brassicae (Plasmodiophorida) triggers endoreduplication in infected plants. For the first time, we also demonstrated pathogen-induced endoreduplication in brown algae infected with Maullinia ectocarpii and Maullinia braseltonii (Phagomyxida). We identified molecular signatures of endoreduplication in RNA-seq datasets of P. brassicae-infected Brassica oleracea and M. ectocarpii-infected Ectocarpus siliculosus.

Discussion

Cell cycle switch proteins such as CCS52A1 and B in plants, CCS52 in algae, and the protein kinase WEE1 in plants were upregulated in RNA-seq datasets hinting at a potential role in the phytomyxean-induced transition from mitotic cell cycle to endocycle. By demonstrating the consistent induction of endoreduplication in hosts during phytomyxid infections, our study expands our understanding of Phytomyxea-host interaction. The induction of this cellular mechanism by phytomyxid parasites in phylogenetically distant hosts further emphasizes the importance of endoreduplication in these biotrophic interactions.

Plasmodiophora brassicae Effector PbPE23 Induces Necrotic Responses in Both Host and Nonhost Plants

Plasmodiophora brassicae is an obligate biotroph that causes clubroot disease in cruciferous plants, including canola and Arabidopsis. In contrast to most known bacterial, oomycete, and fungal pathogens that colonize at the host apoplastic space, the protist P. brassicae establishes an intracellular colonization within various types of root cells and secretes a plethora of effector proteins to distinct cellular compartments favorable for the survival and growth of the pathogen during pathogenesis. Identification and functional characterization of P. brassicae effectors has been hampered by the limited understanding of this unique pathosystem. Here, we report a P. brassicae effector, PbPE23, containing a serine/threonine kinase domain, that induces necrosis after heterologous expression by leaf infiltration in both host and nonhost plants. Although PbPE23 is an active kinase, the kinase activity itself is not required for triggering necrosis in plants. PbPE23 shows a nucleocytoplasmic localization in Nicotiana benthamiana, and its N-terminal 25TPDPAQKQ32 sequence, resembling the contiguous hydrophilic TPAP motif and Q-rich region in many necrosis and ethylene inducing peptide 1-like proteins from plant-associated microbes, is required for the induction of necrosis. Furthermore, transcript profiling of PbPE23 reveals its high expression at the transition stages from primary to secondary infection, suggesting its potential involvement in the development of clubroot disease.

Changes in primary metabolism and associated gene expression during host-pathogen interaction in clubroot resistance of Brassica napus

The role of primary metabolism during Brassica napus-Plasmodiophora brassicae interaction leading to clubroot resistance has not yet been investigated thoroughly. In this study, we investigated some of the primary metabolites and their derivatives as well as expression of the genes involved in their biosynthesis to decipher this host-pathogen interaction. For this, two sets (clubroot resistant and susceptible) of canola lines were inoculated with P. brassicae pathotype 3A to investigate the endogenous levels of primary metabolites at 7-, 14-, and 21-days after inoculation (DAI). The associated pathways were curated, and expression of the selected genes was analyzed using qRT-PCR. Our results suggested the possible involvement of polyamines (spermidine and spermine) in clubroot susceptibility. Some of the amino acids were highly abundant at 7- or 14-DAI in both resistant and susceptible lines; however, glutamine and the amino acid derivative phenylethylamine showed higher endogenous levels in the resistant lines at later stages of infection. Organic acids such as malic, fumaric, succinic, lactic and citric acids were abundant in the susceptible lines. Conversely, the abundance of salicylic acid (SA) and the expression of benzoate/salicylate carboxyl methyltransferase (BSMT) were higher in the resistant lines at the secondary stage of infection. A reduced disease severity index and gall size were observed when exogenous SA (1.0 mM) was applied to susceptible B. napus; this further supported the role of SA in clubroot resistance. In addition, a higher accumulation of fatty acids and significant upregulation of the pathway genes, glycerol-3-phosphate dehydrogenase (GPD) and amino alcohol phosphotransferase (AAPT) were observed in the resistant lines at 14- and 21-DAI. In contrast, some of the fatty acid derivatives such as phosphatidylcholines represented a lower level in the resistant lines. In conclusion, our findings provided additional insights into the possible involvement of primary metabolites and their derivatives in clubroot resistance.

Switching perspectives: The roles of plant cellular reprogramming during nematode parasitism

We propose exploring plant biotrophic parasitism from both a pathogen‐centred and a plant‐centred perspective. This can generate novel research questions and reveal common plant mitigation strategies in response to biotrophic pathogens.

Integration analysis of ATAC-seq and RNA-seq provides insight into fatty acid biosynthesis in Schizochytrium limacinum under nitrogen limitation stress

BACKGROUND

Schizochytrium limacinum holds significant value utilized in the industrial-scale synthesis of natural DHA. Nitrogen-limited treatment can effectively increase the content of fatty acids and DHA, but there is currently no research on chromatin accessibility during the process of transcript regulation. The objective of this research was to delve into the workings of fatty acid production in S. limacinum by examining the accessibility of promoters and profiling gene expressions.

RESULTS

Results showed that differentially accessible chromatin regions (DARs)-associated genes were enriched in fatty acid metabolism, signal transduction mechanisms, and energy production. By identifying and annotating DARs-associated motifs, the study obtained 54 target transcription factor classes, including BPC, RAMOSA1, SPI1, MYC, and MYB families. Transcriptomics results revealed that several differentially expressed genes (DEGs), including SlFAD2, SlALDH, SlCAS1, SlNSDHL, and SlDGKI, are directly related to the biosynthesis of fatty acids, meanwhile, SlRPS6KA, SlCAMK1, SlMYB3R1, and SlMYB3R5 serve as transcription factors that could potentially influence the regulation of fatty acid production. In the integration analysis of DARs and ATAC-seq, 13 genes were identified, which were shared by both DEGs and DARs-associated genes, including SlCAKM, SlRP2, SlSHOC2, SlTN, SlSGK2, SlHMP, SlOGT, SlclpB, and SlDNAAF3.

CONCLUSIONS

SlCAKM may act as a negative regulator of fatty acid and DHA synthesis, while SlSGK2 may act as a positive regulator, which requires further study in the future. These insights enhance our comprehension of the processes underlying fatty acid and DHA production in S. limacinum. They also supply a foundational theoretical framework and practical assistance for the development of strains rich in fatty acids and DHA.

Plasmodiophora brassicae affects host gene expression by secreting the transcription factor-type effector PbZFE1

The protist pathogen Plasmodiophora brassicae hijacks the metabolism and development of host cruciferous plants and induces clubroot formation, but little is known about its regulatory mechanisms. Previously, the Pnit2int2 sequence, a sequence around the second intron of the nitrilase gene (BrNIT2) involved in auxin biosynthesis in Brassica rapa ssp. pekinensis, was identified as a specific promoter activated during clubroot formation. In this study, we hypothesized that analysis of the transcriptional regulation of Pnit2int2 could reveal how P. brassicae affects the host gene regulatory system during clubroot development. By yeast one-hybrid screening, the pathogen zinc finger protein PbZFE1 was identified to specifically bind to Pnit2int2. Specific binding of PbZFE1 to Pnit2int2 was also confirmed by electrophoretic mobility shift assay. The binding site of PbZFE1 is essential for promoter activity of Pnit2int2 in clubbed roots of transgenic Arabidopsis thaliana (Pnit2int2-2::GUS), indicating that PbZFE1 is secreted from P. brassicae and functions within plant cells. Ectopic expression of PbZEF1 in A. thaliana delayed growth and flowering time, suggesting that PbZFE1 has significant impacts on host development and metabolic systems. Thus, P. brassicae appears to secrete PbZFE1 into host cells as a transcription factor-type effector during pathogenesis.

Natural variation in Arabidopsis responses to Plasmodiophora brassicae reveals an essential role for Resistance to Plasmodiophora brasssicae 1 (RPB1)

Despite the identification of clubroot resistance genes in various Brassica crops our understanding of the genetic basis of immunity to Plasmodiophora brassicae infection in the model plant Arabidopsis thaliana remains limited. To address this issue, we performed a screen of 142 natural accessions and identified 11 clubroot-resistant Arabidopsis lines. Genome-wide association analysis identified several genetic loci significantly linked with resistance. Three genes from two of these loci were targeted for deletion by CRISPR/Cas9 mutation in resistant accessions Est-1 and Uod-1. Deletion of Resistance to Plasmodiophora brassicae 1 (RPB1) rendered both lines susceptible to the P. brassicae pathotype P1+. Further analysis of rpb1 knock-out Est-1 and Uod-1 lines showed that the RPB1 protein is required for activation of downstream defence responses, such as the expression of phytoalexin biosynthesis gene CYP71A13. RPB1 has recently been shown to encode a cation channel localised in the endoplasmic reticulum. The clubroot susceptible Arabidopsis accession Col-0 lacks a functional RPB1 gene; when Col-0 is transformed with RPB1 expression driven by its native promoter it is capable of activating RPB1 transcription in response to infection, but this is not sufficient to confer resistance. Transient expression of RPB1 in Nicotiana tabacum induced programmed cell death in leaves. We conclude that RPB1 is a critical component of the defence response to P. brassicae infection in Arabidopsis, acting downstream of pathogen recognition but required for the elaboration of effective resistance.

Phagocytosis underpins the biotrophic lifestyle of intracellular parasites in the class Phytomyxea (Rhizaria)

Phytomyxea are intracellular biotrophic parasites infecting plants and stramenopiles, including the agriculturally impactful Plasmodiophora brassicae and the brown seaweed pathogen Maullinia ectocarpii. They belong to the clade Rhizaria, where phagotrophy is the main mode of nutrition. Phagocytosis is a complex trait of eukaryotes, well documented for free-living unicellular eukaryotes and specific cellular types of animals. Data on phagocytosis in intracellular, biotrophic parasites are scant. Phagocytosis, where parts of the host cell are consumed at once, is seemingly at odds with intracellular biotrophy. Here we provide evidence that phagotrophy is part of the nutritional strategy of Phytomyxea, using morphological and genetic data (including a novel transcriptome of M. ectocarpii). We document intracellular phagocytosis in P. brassicae and M. ectocarpii by transmission electron microscopy and fluorescent in situ hybridization. Our investigations confirm molecular signatures of phagocytosis in Phytomyxea and hint at a small specialized subset of genes used for intracellular phagocytosis. Microscopic evidence confirms the existence of intracellular phagocytosis, which in Phytomyxea targets primarily host organelles. Phagocytosis seems to coexist with the manipulation of host physiology typical of biotrophic interactions. Our findings resolve long debated questions on the feeding behaviour of Phytomyxea, suggesting an unrecognized role for phagocytosis in biotrophic interactions.

Getting to the root of a club - Understanding developmental manipulation by the clubroot pathogen

Plasmodiophora brassicae Wor., the clubroot pathogen, is the perfect example of an "atypical" plant pathogen. This soil-borne protist and obligate biotrophic parasite infects the roots of cruciferous crops, inducing galls or clubs that lead to wilting, loss of productivity, and plant death. Unlike many other agriculturally relevant pathosystems, research into the molecular mechanisms that underlie clubroot disease and Plasmodiophora-host interactions is limited. After release of the first P. brassicae genome sequence and subsequent availability of transcriptomic data, the clubroot research community have implicated the involvement of phytohormones during the clubroot pathogen's manipulation of host development. Herein we review the main events leading to the formation of root galls and describe how modulation of select phytohormones may be key to modulating development of the plant host to the benefit of the pathogen. Effector-host interactions are at the base of different strategies employed by pathogens to hijack plant cellular processes. This is how we suspect the clubroot pathogen hijacks host plant metabolism and development to induce nutrient-sink roots galls, emphasizing a need to deepen our understanding of this master manipulator.

The clubroot pathogen Plasmodiophora brassicae: A profile update

BACKGROUND

Plasmodiophora brassicae is the causal agent of clubroot disease of cruciferous plants and one of the biggest threats to the rapeseed (Brassica napus) and brassica vegetable industry worldwide.

DISEASE SYMPTOMS

In the advanced stages of clubroot disease wilting, stunting, yellowing, and redness are visible in the shoots. However, the typical symptoms of the disease are the presence of club-shaped galls in the roots of susceptible hosts that block the absorption of water and nutrients.

HOST RANGE

Members of the family Brassicaceae are the primary host of the pathogen, although some members of the family, such as Bunias orientalis, Coronopus squamatus, and Raphanus sativus, have been identified as being consistently resistant to P. brassicae isolates with variable virulence profile.

TAXONOMY

Class: Phytomyxea; Order: Plasmodiophorales; Family: Plasmodiophoraceae; Genus: Plasmodiophora; Species: Plasmodiophora brassicae (Woronin, 1877).

DISTRIBUTION

Clubroot disease is spread worldwide, with reports from all continents except Antarctica. To date, clubroot disease has been reported in more than 80 countries.

PATHOTYPING

Based on its virulence on different hosts, P. brassicae is classified into pathotypes or races. Five main pathotyping systems have been developed to understand the relationship between P. brassicae and its hosts. Nowadays, the Canadian clubroot differential is extensively used in Canada and has so far identified 36 different pathotypes based on the response of a set of 13 hosts.

EFFECTORS AND RESISTANCE

After the identification and characterization of the clubroot pathogen SABATH-type methyltransferase PbBSMT, several other effectors have been characterized. However, no avirulence gene is known, hindering the functional characterization of the five intercellular nucleotide-binding (NB) site leucine-rich-repeat (LRR) receptors (NLRs) clubroot resistance genes validated to date.

IMPORTANT LINK

Canola Council of Canada is constantly updating information about clubroot and P. brassicae as part of their Canola Encyclopedia: https://www.canolacouncil.org/canola-encyclopedia/diseases/clubroot/.

PHYTOSANITARY CATEGORIZATION

PLADBR: EPPO A2 list; Annex designation 9E.

Mapping of a novel clubroot disease resistance locus in Brassica napus and related functional identification

Clubroot disease, caused by Plasmodiophora brassicae, is a devastating disease that results in substantial yield loss in Brassicaceae crops worldwide. In this study, we identified a clubroot disease resistance (CR) Brassica napus, "Kc84R," which was obtained by mutation breeding. Genetic analysis revealed that the CR trait of "Kc84R" was controlled by a single dominant locus. We used the bulked segregant analysis sequencing (BSA-seq) approach, combined with genetic mapping based on single nucleotide polymorphism (SNP) markers to identify CR loci from the F₂ population derived from crossing CR "Kc84R" and clubroot susceptible "855S." The CR locus was mapped to a region between markers BnSNP14198336 and BnSNP14462201 on the A03 chromosome, and this fragment of 267 kb contained 68 annotated candidate genes. Furthermore, we performed the CR relation screening of candidate genes with the model species Arabidopsis. An ERF family transcriptional activator, BnERF034, was identified to be associated with the CR, and the corresponding Arabidopsis homozygous knockout mutants exhibited more pronounced resistance compared with the wild-type Col-0 and the transgenic lines of BnERF034 in response to P. brassicae infection. Additionally, the expression analysis between resistant and susceptible materials indicated that BnERF034 was identified to be the most likely CR candidate for the resistance in Kc84R. To conclude, this study reveals a novel gene responsible for CR. Further analysis of BnERF034 may reveal the molecular mechanisms underlying the CR of plants and provide a theoretical basis for Brassicaceae resistance breeding.

What Can We Learn from -Omics Approaches to Understand Clubroot Disease?

Clubroot is one of the most economically significant diseases worldwide. As a result, many investigations focus on both curing the disease and in-depth molecular studies. Although the first transcriptome dataset for the clubroot disease describing the clubroot disease was published in 2006, many different pathogen-host plant combinations have only recently been investigated and published. Articles presenting -omics data and the clubroot pathogen Plasmodiophora brassicae as well as different host plants were analyzed to summarize the findings in the richness of these datasets. Although genome data for the protist have only recently become available, many effector candidates have been identified, but their functional characterization is incomplete. A better understanding of the life cycle is clearly required to comprehend its function. While only a few proteome studies and metabolome analyses were performed, the majority of studies used microarrays and RNAseq approaches to study transcriptomes. Metabolites, comprising chemical groups like hormones were generally studied in a more targeted manner. Furthermore, functional approaches based on such datasets have been carried out employing mutants, transgenic lines, or ecotypes/cultivars of either Arabidopsis thaliana or other economically important host plants of the Brassica family. This has led to new discoveries of potential genes involved in disease development or in (partial) resistance or tolerance to P. brassicae. The overall contribution of individual experimental setups to a larger picture will be discussed in this review.

Plasmodiophora brassicae-Triggered Cell Enlargement and Loss of Cellular Integrity in Root Systems Are Mediated by Pectin Demethylation

Gall formation on the belowground parts of plants infected with Plasmodiophora brassicae is the result of extensive host cellular reprogramming. The development of these structures is a consequence of increased cell proliferation followed by massive enlargement of cells colonized with the pathogen. Drastic changes in cellular growth patterns create local deformities in the roots and hypocotyl giving rise to mechanical tensions within the tissue of these organs. Host cell wall extensibility and recomposition accompany the growth of the gall and influence pathogen spread and also pathogen life cycle progression. Demethylation of pectin within the extracellular matrix may play an important role in P. brassicae-driven hypertrophy of host underground organs. Through proteomic analysis of the cell wall, we identified proteins accumulating in the galls developing on the underground parts of Arabidopsis thaliana plants infected with P. brassicae. One of the key proteins identified was the pectin methylesterase (PME18); we further characterized its expression and conducted functional and anatomic studies in the knockout mutant and used Raman spectroscopy to study the status of pectin in P. brassicae-infected galls. We found that late stages of gall formation are accompanied with increased levels of PME18. We have also shown that the massive enlargement of cells colonized with P. brassicae coincides with decreases in pectin methylation. In pme18-2 knockout mutants, P. brassicae could still induce demethylation; however, the galls in this line were smaller and cellular expansion was less pronounced. Alteration in pectin demethylation in the host resulted in changes in pathogen distribution and slowed down disease progression. To conclude, P. brassicae-driven host organ hypertrophy observed during clubroot disease is accompanied by pectin demethylation in the extracellular matrix. The pathogen hijacks endogenous host mechanisms involved in cell wall loosening to create an optimal cellular environment for completion of its life cycle and eventual release of resting spores facilitated by degradation of demethylated pectin polymers.

Molecular Pathotyping of Plasmodiophora brassicae-Genomes, Marker Genes, and Obstacles

Here we review the usefulness of the currently available genomic information for the molecular identification of pathotypes. We focused on effector candidates and genes implied to be pathotype specific and tried to connect reported marker genes to Plasmodiophora brassicae genome information. The potentials for practical applications, current obstacles and future perspectives are discussed.

A sustained CYCLINB1;1 and STM expression in the neoplastic tissues induced by Rhodococcus fascians on Arabidopsis underlies the persistence of the leafy gall structure

is a gram-positive phytopathogen that infects a wide range of plant species. The actinomycete induces the formation of neoplastic growths, termed leafy galls, that consist of a gall body covered by small shoots of which the outgrowth is arrested due to an extreme form of apical dominance. In our previous work, we demonstrated that in the developing gall, auxin drives the transdifferentiation of parenchyma cells into vascular elements. In this work, with the use of transgenic Arabidopsis thaliana plants carrying molecular reporters for cell division (pCYCB1;1:GUS) and meristematic activity (pSTM:GUS), we analyzed the fate of cells within the leafy gall. Our results indicate that the size of the gall body is determined by ongoing mitotic cell divisions as illustrated by strong CYCB1;1 expression combined with the de novo formation of new meristematic areas triggered by STM expression. The shoot meristems that develop in the peripheral parts of the gall are originating from high ectopic STM expression. Altogether the presented data provide further insight into the cellular events that accompany the development of leafy galls in response to R. fascians infection.

Insights of Molecular Mechanism of Xylem Development in Five Black Poplar Cultivars

Black poplar (Populus deltoides, P. nigra, and their hybrids) is the main poplar cultivars in China. It offers interesting options of large-scale biomass production for bioenergy due to its rapid growth and high yield. Poplar wood properties were associated with chemical components and physical structures during wood formation. In this study, five poplar cultivars, P. euramericana 'Zhonglin46' (Pe1), P. euramericana 'Guariento' (Pe2), P. nigra 'N179' (Pn1), P. deltoides 'Danhong' (Pd1), and P. deltoides 'Nanyang' (Pd2), were used to explore the molecular mechanism of xylem development. We analyzed the structural differences of developing xylem in the five cultivars and profiled the transcriptome-wide gene expression patterns through RNA sequencing. The cross sections of the developing xylem showed that the cell wall thickness of developed fiber in Pd1 was thickest and the number of xylem vessels of Pn1 was the least. A total of 10,331 differentially expressed genes were identified among 10 pairwise comparisons of the five cultivars, most of them were related to programmed cell death and secondary cell wall thickening. K-means cluster analysis and Gene Ontology enrichment analysis showed that the genes highly expressed in Pd1 were related to nucleotide decomposition, metabolic process, transferase, and microtubule cytoskeleton; whereas the genes highly expressed in Pn1 were involved in cell wall macromolecule decomposition and polysaccharide binding processes. Based on a weighted gene co-expression network analysis, a large number of candidate regulators for xylem development were identified. And their potential regulatory roles to cell wall biosynthesis genes were validated by a transient overexpression system. This study provides a set of promising candidate regulators for genetic engineering to improve feedstock and enhance biofuel conversion in the bioenergy crop Populus.

Genius Architect or Clever Thief-How Plasmodiophora brassicae Reprograms Host Development to Establish a Pathogen-Oriented Physiological Sink

When plants are infected by Plasmodiophora brassicae, their developmental programs are subjected to extensive changes and the resultant clubroot disease is associated with formation of large galls on underground tissue. The pathogen's need to build an efficient feeding site as the disease progresses drives these changes, ensuring successful production of resting spores. This developmental reprogramming is an outcome of interactions between the pathogen and the infected host. During disease progression, we can observe alteration of growth regulator dynamics, patterns of cell proliferation and differentiation, increased cell expansion, and eventual cell wall degradation as well as the redirection of nutrients toward the pathogen. Recently, detailed studies of anatomical changes occurring during infection and studies profiling transcriptional responses have come together to provide a clearer understanding of the sequence of events and processes underlying clubroot disease. Additionally, genome sequencing projects have revealed P. brassicae's potential for the production of signaling molecules and effectors as well as its requirements and capacities with respect to taking up host nutrients. Integration of these new findings together with physiological studies can significantly advance our understanding of how P. brassicae brings about reprogramming of host development. This article summarizes the current state of knowledge on cellular changes induced by P. brassicae infection and aims to explain their impact and importance for both the host and the pathogen.