Using knowledge on plant hormone metabolism by Plasmodiophora brassicae - a possibility to control the clubroot pathogen?

DIANA SEIDLER; JUTTA LUDWIG-MÜLLER; REGINA MENCIA; SABINE JÜLKE; ELINA WELCHEN

Edmonton

Workshop; 2018 International Clubroot Workshop, Edmonton, Alberta, Canada; 2018

Clubroot disease symptoms in the Brassicaceae, caused by the soilborne obligate biotrophic pathogenPlasmodiophora brassicae, are determined by the modulation of plant hormones such as auxins andcytokinins, inducing hypertrophy and metabolic sinks in the root galls. Alterations in defense hormonescan also occur. Arabidopsis thaliana is used as a model host to understand the molecular biologyunderlying these processes. The genome sequence of P. brassicae has opened up novel approaches tostudy this pathogen. We could identify several genes encoding putative plant hormone metabolizingenzymes, such as a SABATH-type methyltransferase, but also a GH3-family protein involved in theconjugation and thereby inactivation of indole-3-acetic and jasmonic acids. Further, a functionalcytokinin oxidase was found. We have studied why the treatment of host plants with the defensecompound salicylic acid (SA) did not result in increased tolerance and found that the methyltransferaseis able to methylate mainly SA and to a lesser extent benzoic and anthranilic acids. Overexpression ofthis gene, PbBSMT, in Arabidopsis resulted in plants more susceptible to the clubroot pathogen. Selected mutants with higher constitutive levels of SA, however, were more tolerant to P. brassicae. The possibleroles for the other plant hormone metabolizing enzymes was discussed.