Abstract
Background Clubroot disease is caused by Plasmodiophora brassicae (Phytomyxea, Rhizaria) and is one of the economically most important diseases of brassica crops. The formation of the typical hypertrophied roots is accompanied by altered metabolism and hormone homeostasis of infected plants. Not all roots of an infected plant show the same phenotypic changes: while some roots remain uninfected, others develop galls of diverse sizes. Aim of this study was to analyse and compare the intra-plant heterogeneity of P. brassicae, root galls and symptomless roots of the same host plants (Brassica oleracea var. gongylodes) collected from a commercial field in Austria using transcriptome analyses.
Results Symptomless roots did show transcriptomic traits that had previously described for resistant plants: Genes involved in host cell wall metabolism or salicylic acid (SA) mediated defence response were up-regulated in symptomless roots, while being down-regulated in gall tissues. Transcriptomes between symptomless roots and gall tissue were markedly different, with those differences being in accordance with visible physiological differences between the two tissues. On the pathogen side, a secreted SA methyl transferase (PbBSMT) was one of the highest expressed genes in gall tissues.
Conclusions Infected and uninfected roots of the same clubroot infected plant showed transcriptomic differences which were previously only observed between clubroot resistant and susceptible hosts. We provide further evidence for the biological relevance of PbBSMT which on the one hand likely causes a decrease of SA in the galls, while the PbBSMT produced Methyl-SA potentially leads to increased pathogen tolerance in uninfected roots. The here described intra-plant heterogeneity was unexpected and highlights the need for targeted analyses of clubroot interaction using cell, tissue type, organ specific probing to identify traits that prevent the formation of clubroot disease.
- List of abbreviations
- ABA
- Abscisic acid
- BR
- Brassinosteroids
- C
- Control
- CDS
- Coding sequence
- CK
- Cytokinin
- COG
- Clusters of Orthologous Groups
- DEG
- Differentially expressed gene
- dpi
- days post inoculation
- ET
- Ethylene
- FDR
- False discovery rate
- FPKM
- Fragments per kilobase per million
- HR
- hypersensitive response
- IsoPct
- Isoform percentage
- JA
- Jasmonic acid
- MeSA
- Methyl-salicylate
- NCBI
- National Center for Biotechnology Information
- OG
- Older root gall
- ORF
- Open reading frame
- PbraAT
- Austrian P. brassicae field population
- PR
- Pathogenesis related
- RNA
- Ribonucleic acid
- SA
- Salicylic acid
- SAM
- S-adenosylmethionine
- SL
- Symptomless root
- TAIR
- The Arabidopsis Information Resource
- YG
- Younger root gall