Plants defense responses can be triggered by endogenous elicitors, which are released upon pathogen infection or mechanical injury, indicated as damage-associated molecular patterns (DAMPs). Oligogalacturonides (OGs), cell wall fragments derived from the degradation of the homogalacturonan, are a well-known class of DAMPs. The accumulation of active OGs in vivo is favored by the interaction of microbial polygalacturonases (PGs) with plant PG-inhibiting proteins (PGIPs). Transgenic Arabidopsis plants conditionally expressing a chimeric protein made by a fusion between a fungal PG and a plant-derived PGIP, named "OG machine" (OGM) allow the release on command of OGs in planta and the consequent activation of defense-related responses. If the release of OGs persists plant growth is inhibited and plants eventually die, reflecting the role of the OGs in the so-called growth-defense "trade-off". A homeostatic control, which prevents deleterious effects of the over-accumulation of OGs, may rely on the oxidation of OGs, which impairs their elicitor activity. Four OG oxidases, named OGOX1-4, that belong to the Berberine Bridge Enzyme-like (BBE-like) super-family have been identified in Arabidopsis. Recently it was also discovered that Cellodextrins (CDs), which derive from the cellulose breakdown, act as DAMPs in Arabidopsis. Cellodextrins oxidases (CELLOX), also members of the BBE-like family, are capable of oxidizing CDs. Thus, the homeostatic control of the level of DAMPs to prevent their hyper-accumulation seems to be a general trait of the family of BBE-like. The aim of this project is to elucidate the role of OG and CD oxidases in the Arabidopsis biology by a genome editing approach. Single and double ko mutants for OGOX1 and OGOX2 and triple ogox1/ogox2/cellox mutants will be generated by CRISPR/Cas9 system. Immunity responses and developmental assays will be performed in these mutants in order to unreveal the role of these enzymes in the homeostatic control of DAMPs.
The study of a mechanism for oligosaccharide DAMP oxidation is a new research field in plant biology. Understanding the role of OGs oxidases and CDs oxidases may help us to elucidate the mechanism of homeostatic control of DAMPs leading the way for further studies on possible other oligosaccharide oxidases potentially involved in the homeostasis of different cell wall-derived signals. Knowledge acquired on the role of the DAMP oxidases in the growth-defense trade off may be exploited to improve crops resistance to biotic stresses, associated with an optimization of plant development and growth. The new insights obtained in Arabidopsis thaliana as a model organism can be applied to economically important crop species to increase yield and improve other important agronomic traits.