Establishment of a novel system to elucidate the mechanisms underlying light-induced ripening of strawberry fruit with an Agrobacterium-mediated RNAi technique

Traditional methods used to study strawberry ripening-related gene function are time-consuming, and require at least 15 months from initiating the transformation experiment until the first ripe fruits are available for analysis. To accelerate data acquisition during gene function studies, we explored a transient assay method that employs an Agrobacterium-mediated RNAi (AmRNAi) technique in post-harvest strawberry fruit, Fragaria x ananassa (Fa) cv. Sachinoka, a Japanese cultivar. Our results showed that artificial white light induced strong expression of Fa'chalcone synthase (Fa'CHS), Fa'chalcone isomerase (Fa'CHI), and Fa'flavonoid 3'-hydroxylase orthologues (Fa'F3'H) in post-harvest fruit. Fa'CHS and Fa'F3'H function was subsequently examined by performing AmRNAi with post-harvest fruit. Although reduction of light-induced Fa'F3'H expression by AmRNAi resulted in no significant change in anthocyanin content, reduction of Fa'CHS significantly decreased anthocyanin levels, and up-regulated Fa'F3'H levels. Our results are consistent with previous data indicating that while CHS is required for anthocyanin accumulation during late stage strawberry fruit maturation, Fa'F3'H is not required. The novel system described here enabled gene function data to be available within 10 days of initiating the incubation period following in filtration. therefore, we conclude our system is a valuable tool to elucidate the molecular mechanisms underlying light-induced ripening of strawberry fruit.