Effects of heat treatment on enzyme activity and expression of key genes controlling cell wall remodeling in strawberry fruit.

Modification of cell wall polymers composition and structure is one of the main factors contributing to textural changes during strawberry (Fragaria x ananassa, Duch.) fruit ripening and storage. The present study aimed to provide new data to understand the molecular basis underlying the postharvest preservation of strawberry cell wall structure by heat treatment. Ripe fruit (cv. Aroma) were heat-treated in air oven (3 h at 45 °C) and then stored 8 days at 4 °C + 2 days at 20 °C, while maintaining a set of non-treated fruit as controls. The effect of heat stress on the expression pattern of key genes controlling strawberry cell wall metabolism, as well as some enzymatic activities was investigated. The expression of genes proved to be relevant for pectin disassembly and fruit softening process (FaPG1, FaPLB, FaPLC, FaAra1, FaβGal4) were down-regulated by heat treatment, while the expression of genes being involved in the reinforcement of cell wall as pectin-methylesterase (FaPME1) and xyloglucan endo-transglycosilase (FaXTH1) was up-regulated. Total cell wall amount as well as cellulose, hemicellulose, neutral sugars and ionically and covalently bounded pectins were higher in heat-stressed fruit compared to controls, which might be related to higher firmness values. Interestingly, heat stress was able to arrest the in vitro cell wall swelling process during postharvest fruit ripening, suggesting a preservation of cell wall structure, which was in agreement with a lower growth rate of Botrytis cinerea on plates containing cell walls from heat-stressed fruit when compared to controls.