Damage associated molecular patterns (DAMPs) in plant innate immunity.

Plants have developed an efficient innate immune system to defend themselves against pathogens. They can perceive and recognize pathogens by sensing signals originating from the pathogen (so-called microbe-associated molecular patterns (MAMPs)) or by sensing signals that originate from the plant itself because of damage caused by the pathogen (so-called damage-associated molecular patterns (DAMPs)). In this project we investigated if the degradation products of a group of plant secondary metabolites -glucosinolates- generated upon plant damage and known to have direct toxic effects on insects and pathogens might in addition have a role as DAMPs and as a consequence trigger a plant innate immune response. During the last year we have pursued this investigation through several approaches. Changes in gene expression levels and protein levels when the model plant Arabidopsis thaliana is exposed to these particular DAMPs were analysed in detail to identify important mechanisms. We have continued our characterization of plants in which some of these mechanisms, such as antioxidant capacity or resistance to heat stress, are impaired as these showed a different growth and morphology than normal plants when exposed to these DAMPs. Different experiments were performed to investigate if and how these DAMPs generate oxidative stress, provoke cell death and improve heat stress tolerance. Approaches to identify potential protein targets to which these DAMPs might bind and thereby trigger a response were also implemented and have revealed interesting candidate proteins of unknown function. Other Arabidopsis plants that showed a different growth behavior when exposed to these DAMPs were identified through screening a large collection of mutants generated by chemical mutagenesis. We also have addressed the question in how far the responses of Arabidopsis thaliana to a DAMP treatment depends on the nature and the structure of the DAMPs, revealing that some provoke strong growth inhibition while others only generate small effects. We also found that one of these compounds unexpectedly interferes with the hormone balance of the plant by being a precursor of a hormone molecule. We have generated different tools, which will allow us to further characterize the temporal and spatial distribution of the responses triggered by these DAMPs.

Mechanisms used by plants and animals to resist infection show similarities in both structural and strategic aspects. Plants lack however mobile defender cells or a somatic adaptive immune system and have to rely instead on their two-layered innate immune system to fight against potential pathogens. The first layer called PAMP-triggered immunity (PTI) is mediated by the perception of pathogen- or microbe-associated molecular patterns (PAMPs or MAMPs) through pattern recognition receptors (PRRs) at the pla nt cell surface. The perception of bacterial flagellin by the plant leucine-rich repeat receptor kinase FLS2 is a well studied example of PTI in the model plant Arabidopsis thaliana. It resembles the perception of bacterial flagellin by the mammalian Toll -like receptor 5 (TLR5). The second layer is called effector-triggered immunity (ETI) as it consists in the perception by the plant of so-called effectors that successful pathogens produce to overcome PTI. Another hardly characterized group of danger sign als able to trigger an innate immune response are damage-associated molecular patterns (DAMPs) originating from the attacked plant itself. Here we hypothesize that hydrolysis products of the plant secondary metabolites called glucosinolates act as DAMPs, and we present a tentative model for the mechanisms leading to the perception of these "GAMPs" (for glucosinolate hydrolysis-associated molecular patterns) and a plant innate immune response. Unravelling the perception and signalling mechanisms as well as assessing the nature of the plant innate immune response triggered by GAMPs in the model plant Arabidopsis thaliana is the object of the proposed project. We will use a combination of wet lab molecular biology and biochemistry tools, transcriptomics, pro teomics, bioinformatics and molecular imaging/microscopy to answer the scientific questions asked here. To succeed in our task we have engaged with us an inter-disciplinary network of excellent collaborators.