Unraveling a complex pathosystem with two microbes: Host and pathogen proteomics of the Arabidopsis- Plasmodiophora-Acremonium interaction

Question

Clubroot disease, caused by the soil-borne pathogen Plasmodiophora brassicae, continues to spread worldwide in countries with rapeseed and cabbage production. Currently no efficient control strategies are available for this disease in Europe. The use of biocontrol agents bears untapped potential to help secure crop yields without negative effects on the environment. The biocontrol fungus Acremonium alternatum is a promising candidate for cluboot control as it reduces disease severity and increases survival rates of infected plants (1-3). We studied the interaction of Arabidopsis with P. brassicae and A. alternatum during clubroot disease progression to elucidate the molecular mechanisms behind the observed biocontrol effect. Our goals are i) to contribute to the basic understanding of the clubroot pathogen in interaction with the host and a biocontrol agent and ii) to identify plant targets of the clubroot pathogen that could be exploited for breeding of clubroot-resistant cultivars.

Methods

Proteins were extracted with a gel-free shotgun protocol and samples analysed by nanoflow C18 reverse-phase liquid chromatography using a nano-UPLC system and q-TOF mass spectrometer. Measured spectra were processed and searched against P. brassicae and Arabidopsis protein sequence databases. Protein abundance was estimated by peptide spectral matches. 

Results

At the onset of clubroot resting spore formation we found 150 differentially enriched proteins, among them a root endochitinase and several cytokinin and auxin responsive proteins. Proteome analyses of root galls with fully developed resting spores yielded roughly 300 proteins specific for the clubroot pathogen. The most abundant proteins belonged to the heat shock family, comprising 7% of all identified peptide spectral matches. We also found enrichment of salicylic acid methyltransferase, an enzyme that inactivates salicylic acid.

Conclusion

Our results confirm earlier findings for the highly abundant methyltransferase (4) and revealed new insights into the P. brassicae and host proteome at the end of the infection cycle. Further in-depth analyses of the trancriptome and proteome of this pathosystem are underway.

1 Auer S, Ludwig-Müller J, 2014: Albanian Journal of Agricultural Science, 15.

2 Auer S, Ludwig-Müller J, 2015: Journal of Endocytobiosis and Cell Research, 26: 43-49.

3 Auer S, 2019: http://doi.org/10.5281/zenodo.3236417

4 Ludwig-Müller J et al., 2014: Molecular Plant Pathology, 16: 349–364.