BERBERINE BRIDGE ENZYME-LIKE OXIDASES OF CELLODEXTRINS AND MIXED-LINKED β-GLUCANS CONTROL SEED COAT FORMATION

Abstract

ABSTRACTA member of the Arabidopsis Berberine Bridge Enzyme-like (BBE-l) protein family named CELLODEXTRIN OXIDASE 2 (CELLOX2) has been characterized in this paper and shown to display structural and enzymatic features similar to the previously characterized CELLOX1. These include the capability to oxidize the mixed-linked β-1→3/β-1→4-glucans (MLGs), recently described as cell wall-derived damage-associated molecular patterns (DAMPs) that activate plant immunity. The two paralogous genes show a different expression profile. UnlikeCELLOX1, CELLOX2is not expressed in seedlings or in adult plants and is not involved in immunity againstBotrytis cinerea.Both genes are expressed in a concerted manner in the seed coat during development: whereasCELLOX2transcripts are detected mainly during the heart stage,CELLOX1transcripts are detected later, when the expression ofCELLOX2decreases. Analysis of seeds ofcellox1andcellox2knock-out mutants show alterations in the structure of the coat and mucilage, but not in their monosaccharide composition. We propose that the cell wall structure of specific organs is not only the result of a coordinated synthesis/degradation of polysaccharides but also of their exposure to enzymatic oxidation. Our results also reinforce the view that the family of BBE-l proteins is at least in part devoted to the control of the activity of cell wall-derived oligosaccharides acting as DAMPs.SENTENCETwo Arabidopsis BBE–like oxidases of the cell wall DAMPs cellodextrins and mixed-linked β-glucans inactivate their elicitor activity. Seed coat and mucilage are altered in null mutants of two enzymes.