Several plant Cell Wall (CW)-derived fragments like oligogalacturonides (OGs), cellodextrins (CDs) and mixed-linkage glucans (MLGs) activate plant immunity and behave as typical damage-associated molecular patterns (DAMPs). Due to the antithetic effect of CW-DAMPs on immunity and growth, their homeostasis is critical for the so-called ¿growth-defense trade-off.¿
This project aims at elucidating the role of the CW and CW-DAMPs in plant immunity and development, using Arabidopsis thaliana (AIMS 1-3) and the crop plant Lycopersicum esculentum (tomato) (AIM 4).
AIM 1 is to shed light on the still uncharacterized aspects of the biology of OGs. Only short-term (min/h) defense responses activated by OGs, whereas a long-term (days) transcriptional reprogramming is likely necessary for a durable resistance. Long-term adaptive responses to CW-DAMPs will be studied.
AIM 2 is to characterize a mechanism that controls the homeostasis of CW-DAMPs, played by berberine bridge enzyme-like (BBE-l) proteins. The characterization of this phenomenon may have significant biotechnological applications to overcome the limitations imposed by a deleterious hyper-immunity.
AIM 3 is to characterize proteins that regulate the activity of Pectin Methyl Esterases (PME). PMEs regulate the methyl esterification status of homogalacturonan, which influences how and what types of DAMPs are released. The synthesis, biochemical properties and role of PME regulators will be studied.
AIM 4 is to elucidate the role of tomato PMEs in the apoplastic biosynthesis of Ascorbic Acid (AsA), through a pectin-derived D-galacturonic biosynthetic pathway. The use of tomato will facilitate the translation of the knowledge obtained in this project to an economically relevant crop.
Knowledge gained can be exploited for the effective and safe use of CW-DAMPs in agriculture.
Today, chemical control is the most used and effective strategy in crop protection. The research activity on the immunity of plants has stimulated the development of phytosanitary products based on elicitors, compounds less toxic and more respectful of the environment than conventional agrochemicals, able to activate the natural defense mechanisms of the plant. Among the most studied DAMPs, OGs are able to induce resistance against fungal infections in different plant species [27]. Other CW-DAMPs, such as CDs and mixed-linked oligoglucans, also have the ability to activate defense responses in plants [28]. CW-DAMPs are of particular interest as they are plant products that can be obtained in large quantities from agricultural waste biomass, such as straw, and be used in a circular economy perspective, above all in integrated pest management contexts, where they would have a wider market. The use of elicitors in agriculture today is limited as they could cause fitness costs in crops due to the compromise between resources allocated for growth and reproduction and for resistance to disease [29]. This project will investigate the possibility to uncouple the negative effects of CW-DAMPs on growth from the positive effects on resistance to pathogens. Moreover, our work will help understand the molecular and biochemical mechanisms underlying the mode of action of CW-DAMPs and of their homeostasis, providing new knowledge required for the effective and safe use of these compounds in agriculture. Transcriptomic analyses in Arabidopsis will enable us to identify key genes regulating long-term responses to CW-DAMPs and mediating the balance between growth and defense during plant immunity. The study of the epigenetic mechanisms responsible for the enhanced resistance observed in plants treated with CW-DAMPs will help understand how plants can be protected by these elicitors without major fitness costs. Moreover, through the investigation of the role of CW composition and modifications, and in particular of pectin methylesterification, on resistance to pathogens and on the endogenous release of CW-DAMPs, we will identify novel CW-related traits important in plant-pathogen interactions and the genes that regulate them. Bc, the causal agent of gray mold, is one of the most economically devastating disease [30] and is used in the project as a model to study host responses to pathogens. To date, the principal means to control Bc remain the application of synthetic fungicides with negative environmental impact. The application of CW-DAMPs in crop protection can represent a new promising sustainable alternative. The use of tomato, together with the model plant Arabidopsis, will facilitate the translation of the knowledge obtained in this project to an economically relevant crop. The genes encoding key regulator of CW-DAMP-induced responses and of CW-mediated resistance to infections that will be identified in this project might be used as targets for breeding of novel crop varieties with broad-range resistance to pathogens without negative effects on crop productivity.
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