Mendel University in Brno 

Keynote Lecture 11: Plant hormones in biotic interactions

Jutta Ludwig-Müller [a]

[a] Technische Universität Dresden, Dresden, Germany

Plant hormones control many developmental processes, but also various aspects in the interaction of plants and pathogens. On the one hand, they are involved in defense responses, but on the other hand they control also symptom development. The clubroot disease caused by Plasmodiophora brassicae infects economically important crop species such as canola and causes high yield losses. The symptoms are determined by the modulation of plant hormones such as auxins and cytokinins inducing hypertrophies and metabolic sinks in root galls, but also the status of defense hormones is altered. 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 the protist. 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. Since P. brassicae cannot be routinely transformed, we use heterologous hosts such as Escherichia coli or A. thaliana to determine the function of P. brassicae genes / proteins. The analysis will improve our understanding on the metabolism to fine-tune the hormonal homeostasis of the host. In addition, the disease is difficult to control by chemical and cultural means. Therefore, we study Acremonium alternatum, a soilborne endopyhtic fungus and known biological control agent whether it can circumvent the suppression of plant defense responses by P. brassicae. The long-term goal is to understand how the reduction of clubroot infection of A. thaliana is regulated.