Molecular Actors Involved in the Softening of Fragaria chiloensis Fruit Accelerated by ABA Treatment

Fragaria chiloensis is a native species from Chile and has interesting attributes such as good taste, aroma, and exotic white color. As the maternal relative of commercial strawberry, it is interesting to understand its ripening physiology. Changes in physiological parameters (size, soluble solids, acidity, and firmness) were followed during the development and ripening of F. chiloensis fruit, noticing a fast and intense softening that severely limits its post-harvest shelf life. The content of abscisic acid (ABA) was quantified along its development and displayed an incremental pattern, meanwhile a descendant profile was determined for auxin. To clarify the role of ABA on F. chiloensis softening, detached immature fruits (C2 stage, low ABA levels) were treated with exogenous ABA and changes in firmness were followed during storage at 20 °C. Fruit firmness reduction was accelerated by ABA treatment compared to non-treated fruit, and consistent with that, a clear induction in the accumulation of transcripts of cell wall disassembly genes such as FcPG, FcRGL1, and FcExp5 was observed. In parallel, there was an increment in the transcript level of transcription factors (TFs) such as FcNAC1, FcSEP3, and FcSHP. Good correlations were determined between firmness reduction and the expression of cell wall genes and TFs. Bioinformatic analysis reveals the presence of cis elements responding to ABA in the promoter regions of cell wall disassembly genes and FcNAC1. This indicates that ABA accelerates the set of transcriptional changes leading to softening on this non-climacteric fruit and suggests that these TFs could act as molecular mediators.