Scientific Highlight April 2014

Transcription

1 Scientific Highlight April 2014 Research Unit Microbe-Plant Interactions (AMP) PSP-Elements: G /002 Persons to contact for further enquiries: Prof. Dr. Anton Hartmann, Tel Prof. Dr. Peter Schröder, Tel Title of the Highlight: Bacterial quorum sensing compounds are important modulators of microbe-plant interactions Keywords: Bacterial quorum sensing, microbe-plant interactions, systemic resistance, growth regulation Central statement of the Highlight in one sentence: The response patterns of diverse plants towards the QS-compounds of the N-acyl homoserine lactone type demonstrate major impacts of these signaling compounds on plant development and systemic resistance. Text of the Highlight: Plants are living in tight association with microbes, which colonize not only their surfaces but also internal tissues. During their whole life span, plants and microbes are interacting with each other in symbiotic, saprophytic or pathogenic manner. The plant host and the plant-associated microbiome is forming a holobiontic system, which is characterized by a better adaptability and flexibility towards rapidly changing adverse environmental conditions due to the highly diverse interactions with its microbiome. The plant host is not only recognizing its microbial companions by its specific molecular patterns (usually on its surface) but also by small molecules produced by them. We studied in several plants the response of the plant hosts towards the widely distributed bacterial quorum sensing molecules of the N-acyl homoserine lactone (AHL)-type. Dependent on the detailed molecular structure of the AHLs, the plant hosts responded with specific molecular responses changing the expression profile of specific genes involved in systemic resistance or plant growth regulation. While some plants (like most legumes) have enzymatic activities destroying AHLs efficiently, in other plants, like Arabidopsis or barley, AHLs are quite stable. It 1

2 could be demonstrated, that the more water soluble compounds C4-C8 AHLs are transported through the roots into the shoots and get distributed systemically in the plant shoot. Interestingly, these transport processes are energy-dependent and also seem to use the apoplastic flow through the tissues. In contrast, the response towards lipophilic AHLs is mediated through a signaling cascade. This intimate interaction not only alters the response to the microbial guests but also significantly modulates e.g. anti-enzymatic activities in plant shoots. Also in animal systems, signaling of bacterial AHLs towards host tissues was found. Publication: Hartmann A, Rothballer M, Hense, BA, Schröder P. (2014) Bacterial quorum sensing compounds are important modulators of microbe-plant interactions. Frontiers in Plant Science. doi: /fpls Taking account of the HMGU mission: The sustainable bioeconomy initiative is aiming at utilizing all available bioressources in order to provide high quality food and fiber production as well as making bio-based regenerative energy ressources available. In this context, plant production should be using all means of acquiring optimum nutrient supply and plant health protection in a sustainable and cost-effective way. In this context, the potential of substantial supportive activities of plant-associated microbiota and their interaction with plants to improve abiotic and biotic stress resistance is of high relevance. The internal HMGU co-operation partners with whom the Highlight was compiled, if appropriate: Dr. Burkhard A. Hense, ICB, burkhard.hense@helmholtz-muenchen.de, Tel.: 4035 PD Dr. Susanne Krauss-Etschmann, CPC, krauss-etschmann@helmholtzmuenchen.de, Tel.:

3 Bacterial quorum sensing compounds are important modulators of microbe-plant interactions Helmholtz Zentrum München Research Unit Microbe-Plant Interactions, Prof. Dr. Anton Hartmann, Prof. Dr. Peter Schröder PSP: G /002

4 Introduction: Bacterial quorum sensing signaling using N- acyl homoserine lactones and the responses of plants Bacteria use small diffusible molecules, like N-acyl-homoserine lactones (AHL) (Fig.1) produced by Gram-negative bacteria, as sensors for environmental conditions and for communication within their populations. Since these signalling compounds are produced in an auto-inducing process, their production is extremely stimulated in cell aggregates, micro-colonies and biofilms (see Fig. 2; mathematical calculation of AHL-autoinduction in cell aggregates colonising surfaces). Figure 1: Figure 2: OH O R = C2 - C12 O R N Objectives of the study: - Do higher organisms / holobiotic systems, colonized by QS-active bacteria, respond to QS-molecules? - What kind of responses are induced? - What is the fate of the different types of N-acyl homoserine lactones in plants? O

5 AHL-transport and signal perception in plants (example: barley plant) Influence of AHL-producing bacteria or AHL-compounds on/in roots on the expression patterns and physiological activities in barley plant Shoots: Modulation of enzyme activities, phytohormonal changes Shoots: Systemic resistance development towards pathogenic bacteria and biotrophic fungi; hypersensitive reaction Transpiration, active transport, G-protein receptor Signaling cascade: MAP-kinase-dependent signaling Effect on root development Roots: Short-chain AHLs or short-chain AHL-producing bacteria Roots: Long-chain AHLs or long-chain AHL-producing bacteria

6 N-acyl homoserine lactones and their influence on enzyme activities in root and shoot Influence of short side chain HSLs on enzymatic activities in roots/leaves: - antioxidative A) enzymes: like ascorbate reductase, glutathion B) reductase or superoxide reductase - detoxification enzymes: like cytosolic glutathion-s-transferases (GST) C10-HSL root C6-HSL shoot Example: cytosolic GST-activities in barley C8-HSL shoot While the GST-activities in roots were inhibited, they are increased in shoots in the presence of C6-homoserine lactone. C8-HSL root C10-HSL shoot A C6-HSL root PhD-thesis of Tina Sieper, (2013), AG Plant and Endophyte Physiology, Prof. Dr. Peter Schröder

7 Influences of AHL-compounds on dendritic cells affects ensuing T cell response P. aeruginosa Results in reduced T cell proliferation AHL (3oxoC12 HSL) DC DC T cell Antigen uptake Phagocytosis Migration to lymph node T cell activation Bernatowicz R, Binder T, Nössner E, Rothballer, M, Perez-Velazquez J, Hense BA, Schmid M, Hartmann A, Krauss-Etschmann S (2014) 3-oxo-C12-homoserine lactone from Pseudomonas aeruginosa impairs multiple human dendritic cell functions for priming of T-cells. J. Immunology (in revision)