Physiological and transcriptomic analyses provide new insights into the regulatory mechanisms of accelerated senescence of litchi fruit in response to strigolactones

Strigolactones (SLs), a class of plant hormones that are derived from carotenoid metabolism, play pivotal roles in regulating various physiological processes in plants. However, the action mode of SLs in regulating postharvest physiology of fruits is not well understood. This study aimed to explore the effect of exogenous GR24 (a synthetic analogue of SLs) on litchi senescence and its possible mechanisms based on physiological and transcriptomic analyses. The results demonstrated that GR24 treatment at 0.5 mu M accelerated the development of pericarp browning and discoloration in litchi fruit during storage at ambient conditions, which was related to exacerbated oxidative stress and aggravated membrane deterioration, as indicated by increased reactive oxygen species production, membrane permeability and malondialdehyde content. Compared to those in the control fruit, lower activities of antioxidant enzyme (superoxide dismutase, catalase, glutathione reductase, ascorbate peroxidase and glutathione peroxidase) and contents of antioxidants (ascorbic acid and reduced glutathione), but higher prooxidant enzyme (peroxidase) activity were observed in GR24-treated fruit. Transcriptomic analysis revealed that GR-24 treatment downregulated the expression of genes associated with antioxidant system, pentose phosphate pathway, oxidative phosphorylation and energy metabolism, which was aligned with the physiological results. These findings provide insights into the role of SLs in regulating senescence of harvested litchi fruit.