Softening of F. chiloensis fruit. An effort to understand its hormonal regulation using transcriptomic and genomic analyses

The Chilean strawberry (Fragaria chiloensis) has emerged as a new berry with excellent organoleptic characteristics, however its fast softening is a limiting step for commercialization. F. chiloensis is a non-climacteric fruit and its ripening seems to be coordinated by hormones like auxins (Aux) and abscisic acid (ABA). During ripening Aux levels decrease while that of ABA increases. Softening is related to cell wall dissembling and several related enzymes have been described to take part during softening of F. chiloensis fruit, including polygalacturonase (PG), xyloglucan endotransglycosylase/ hydrolase (XTH1) and expansin 2 (Exp2). The level of their transcripts increases during fruit softening. When the fruit is subjected to several hormonal treatments (Aux, ABA, GA3, ethylene, 1-MCP) in order to establish their effects on the expression of these genes, significant variations are recorded. An activator effect of auxin on the expression of XTH1 and a repressive effect on PG is found. ABA induces the expression of XTH1 and PG, GA3 displays an activator effect on XTH1, Exp2 and PG, and finally 1-MCP represses the expression of PG and Exp2 while induces that of XTH1. To explain this regulatory mechanism, the promoter regions of these genes were obtained by Genome walker, cloned and in silico analyzed to reveal putative cis elements using PlantCARE. The promoters contained several regulatory elements responding to hormones which could explain their differential responsiveness. This provides evidences to clarify the hormonal regulation of key genes during ripening of F. chiloensis fruit. Acknowledgments to Anillo ACT-1110 and Fondecyt 1110792 Projects.