Comparative analysis of fruit firmness and genes associated with cell wall metabolisms in three cultivated strawberries during ripening and postharvest

Cultivated strawberry (Fragaria x ananassa), a world-famous fruit, is subjected to rapid softening during ripening, resulting in a shorter shelf life and severe economic losses during storage and transportation. However, there is limited understanding of the molecular mechanism underlying differences in fruit firmness during ripening and postharvest among cultivated strawberries. Here, we explored this molecular mechanism by comparing three cultivated strawberries via firmness measurement, transcriptome analysis, quantitative real-time polymerase chain reaction, and correlation analysis, and revealed FaEXP7, FaPG2, FaPLA, and Fa beta-Gal4 as potential softening activators expressed before harvest to determine fruit with more softened texture and shorter shelf life, and that extremely high expression levels of FaCEL1-1 and FaCEL1-3 during ripening might be accelerators to intensify this situation. Additionally, both the enzyme activities of FaCEL and the expression pattern of FaCEL1-3 showed a significantly negative correlation with fruit firmness after harvest, suggesting that FaCEL1-3 might play a key role in promoting strawberry fruit softening not only during ripening but also postharvest. These results showed that the difference in fruit firmness and shelf life among cultivated strawberries was controlled by the temporal expression pattern of a legion of cell wall-associated genes during ripening and postharvest.