The identification of different berberine bridge enzyme-like (BBE-l) proteins from Arabidopsis thaliana as specific oligosaccharide oxidases (OSOXs) paved the way to novel insights in plant immunity. The enzymatic hydrolysis of cell wall polysaccharides results in the initial accumulation of cell wall fragments that can be perceived by plants as danger signals 3 as the pathogen attack continues, these cell wall fragments are progressively converted into dimers and monomers that microbes use as carbon source to sustain their infection process 1, 4.

Phytopathogenic fungi decompose the cell wall by the action of several cell wall degrading enzymes (CWDEs), a large group of enzymes that includes glycoside hydrolases (GHs), lyases and oxidoreductases 1, 2. the cell wall, and a sophisticated defense system that can be promptly activated at the occurrence.

Against them, plants evolved a robust barrier composed of polysaccharides, phenols and proteins, i.e. Plants are constantly menaced by a wide array of pathogens such as viruses, bacteria and fungi. In contrast to the oxidation of longer oligomers such as OGs (degree of polymerization from 10 to 15), the activity of OSOXs on short galacturonan- and cellulose-oligomers (degree of polymerization ≤ 4) successfully counteracted the radical cation-generating activity of a fungal laccase, suggesting that OSOXs can generate radical cation scavenging activity in the apoplast with a power proportional to the extent of degradation of the plant cell wall, with possible implications for redox homeostasis and defense against oxidative stress.

+ with an efficiency dependent on the type and length of the oxidized oligosaccharide.

+-reduction assay, we identified a novel reaction mechanism through which the activity of OSOXs on cell wall oligosaccharides scavenged the radical cation ABTS.

Little is known about the physiological role of OSOX activity. Oligogalacturonide-oxidases (OGOXs) and cellodextrin-oxidase (CELLOX) are plant berberine bridge enzyme-like oligosaccharide-oxidases (OSOXs) that oxidize, respectively, oligogalacturonides (OGs) and cellodextrins (CDs), thereby inactivating their elicitor nature and concomitantly releasing H 2O 2.

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