Over-expression of the carbohydrate-binding module of Solanum lycopersicum expansin 1 (SLEXP1) modifies susceptibility to Botrytis cinerea

PERINI, MA; SIN, IN; VILLARREAL, NM; MARINA M; NARDI, CF; ROSSI FR; MARTINEZ, GA; POWELL, ALT; CIVELLO, PM

Santa Cruz

Simposio; XVII INTERNATIONAL BOTRYTIS SYMPOSIUM; 2016

Fruit firmness depends largely on the mechanical resistance imposed by cell walls and wall integrity is a major determinant of postharvest quality, shelf life and disease resistance. Botrytis cinerea causes gray mold disease and, as a necrotophic opportunistic plant pathogenic fungus, contributes substantially to the postharvest decay of fleshy fruits. Multiple strategies have been evaluated to control firmness losses during storage and, thereby, reduce susceptibility to pathogen infections. Most of the approaches have been designed to suppress the expression of key enzymes involved in fruit cell wall metabolism. Expansins (EXPs), modular extracellular plant proteins with a characteristic putative catalytic domain and a carbohydrate-binding module (CBM) common in many carbohydrate-associated proteins, are involved in the non-hydrolytic metabolic disassembly of plant cell walls, especially when relaxation of the wall is necessary, such as during fruit development and ripening. Previous work has shown that expansins influence firmness, cell wall metabolism and susceptibility to B. cinerea. Overexpression of the just the CBM module of strawberry expansin 2 in A. thaliana modified cell wall metabolism and increased resistance to B. cinerea. Suppression of tomato fruit SlEXP1 expression reduced susceptibility to B. cinerea and A. alternata. Simultaneous suppression of the tomato ripening-associated polygalacturonase and SlEXP1 resulted in tomato fruit less susceptible to B. cinerea. Transgenic tomato lines overproducing the S. lycopersicum expansin 1 CBM (CBM-SlEXP1) peptide in the cell wall were generated to test thesis that the endogenous CBM itself influences wall metabolism and infection susceptibility. CBM-SlEXP1 overexpression increased the mechanical resistance of leaves and fruit firmness, delayed ripening-associated softening and reduced symptoms in ripe fruit of B. cinerea infections. Furthermore, the growth of B. cinerea was reduced in solid media containing polysaccharides extracted from CBM-SlEXP1 expressing. These results suggest that the overexpression of just the CBM from SlEXP1 might influence the course of a pathogen infection, possibly due to modifications of the overall cell wall structure and/or by altering the accessibility of fruit?s cell wall polysaccharides to Botrytis or host cell wall degrading enzymes.