Transcriptomic and physiological analysis reveals the possible mechanism of ultrasound inhibiting strawberry postharvest softening

caomeiUltrasound can effectively inhibit strawberry softening while the mechanism is not clear. In this study, transcriptome sequencing and physiological data were combined to explore the mechanism of strawberry response to ultrasonic treatment. Physiological results indicate that the firmness decline was inhibited and the contents of soluble pectin (SP) were reduced in ultrasound treated strawberries during late storage period, compared with the control. Ultrasound delayed the time of pectin-degrading enzymes pectin esterase (PE) and polygalacturonase (PG) activity reached the peak and suppressed their activities significantly in late storage period. Besides, the contents of signal substances hydrogen peroxide (H2O2) and ethylene had response to ultrasound treatment in early and late storage stage. Transcriptome sequencing results showed that gene expression mainly respond to ultrasound treatment during the first 12 h of storage. Key genes in reactive oxygen species (ROS), ethylene (ET), jasmonic acid (JA) as well as other hormone signaling pathways and WRKY family differentially expressed during storage. Physiological and transcriptomic findings revealed a hypothetical mechanism model as follows: ultrasound enhanced ROS scavenging and activated JA biosynthesis, which acts as a signal for delaying the activation of ET signaling pathway, thus suppressing the activity of pectin-degrading enzymes PE and PG, and ultimately inhibiting postharvest softening in strawberry.