Dottorato in BIOLOGIA CELLULARE E DELLO SVILUPPO

Titolo della tesi: Improved pathogen resistance in plants through on command release of pectin-derived damage-associated molecular patterns (DAMPs)

Recognition of endogenous molecules acting as “Damage-Associated Molecular Patterns” (DAMPs) is a key feature in plant defense strategy. A well-known class of DAMPs is made by Oligogalacturonides (OGs), cell wall fragments derived from the degradation of the homogalacturonan. The interaction of microbial Polygalacturonases (PGs) with plant-derived inhibitors (PGIPs) promotes the accumulation of OGs in vivo. Transgenic Arabidopsis thaliana plants expressing an inducible PGIP-PG chimera, named "OG machine" (OGM), have been generated, allowing the release on command of OGs in planta. If the command persists plant development is inhibited, reflecting a role of the OGs in the so-called growth-defense “trade-off”. To genetically dissect the molecular mechanism involved in plant defense against pathogens and the key aspects of the trade-off between development and defense that takes place in response to the OGM action, plants expressing the OGM in the defective mutant background of key elements involved in immunity have been generated. One of the OGM phenotype, i.e. inhibition of the root growth, is totally recovered in rbohDxOGM and jar1.1xOGM and partially recovered in eds1-2xOGM double mutants. The compromised radical growth of the OGM is connected to an altered root meristem, consisting of a decreased number of cells. In plants expressing the OG-machine in an eds1-2, rbohD, or jar1.1 background, this meristematic defect is not observed. Furthermore, I observed that OGM expressed in rbohD and eds1-2 mutant backgrounds leads to a higher resistance against the necrotrophic fungus Botrytis cinerea. This resistance seems to be not dependent on ROS generated by RBOHD, a membrane NADPH oxidase. The study of the transcriptome of OGM expressing plants sheds light on the signaling pathways activated by the OGs. Moreover, preliminary results suggest that OGs derived from OGM play a negative role in grafting and tissue regeneration, probably antagonizing the auxin vascular formation activity in wounding healing