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

JÜLKE S; SEIDLER D; MENCIA R; LUDWIG-MULLER J; WELCHEN E

Workshop; 2018 International Clubroot Workshop; 2018

Clubroot disease symptoms in the Brassicaceae, caused by the soilborne obligate biotrophic pathogen Plasmodiophora brassicae, are determined by the modulation of plant hormones such as auxins and cytokinins, inducing hypertrophy and metabolic sinks in the root galls. Alterations in defense hormones can also occur. Arabidopsis thaliana is used as a model host to understand the molecular biology underlying these processes. The genome sequence of P. brassicae has opened up novel approaches to study this pathogen. We could identify several genes encoding putative plant hormone metabolizing enzymes, such as a SABATH-type methyltransferase, but also a GH3-family protein involved in the conjugation and thereby inactivation of indole-3-acetic and jasmonic acids. Further, a functional cytokinin oxidase was found. We have studied why the treatment of host plants with the defense compound salicylic acid (SA) did not result in increased tolerance and found that the methyltransferase is able to methylate mainly SA and to a lesser extent benzoic and anthranilic acids. Overexpression of this 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 possible roles for the other plant hormone metabolizing enzymes was discussed.