The interaction between CmPIF8 and CmACO1 under postharvest red light treatment might affect fruit ripening and sucrose accumulation in oriental melon fruit

Light and plant hormones are involved in regulating the growth, development and fruit quality formation. However, it remains unclear whether light regulates the fruit quality of oriental melon by affecting hormones. Sucrose is mainly accumulated in mature oriental melon fruit, and the accumulation of sucrose is closely related to ethylene. Here, the climacteric melon fruit 'HS' were treated with red and blue light at ethylene release initial stage (30 d after anthesis, DAA), and the results showed that the red light treatment enhanced the production of ethylene and the activity of 1-aminocyclopropane-1-carboxylate oxidase (ACO), as well as CmACO1 expression in melon fruit at postharvest stage. Red light also up-regulated the sucrose accumulation and the activity of sucrose phosphate synthetase (SPS) and CmSPS1 expression in postharvest melon fruit. Moreover, we found that PHYTOCHROME INTERACTING FACTOR 8 (PIF8), as a negative regulator of ethylene biosynthesis by directly binding to CmACO1 promoter. In summary, red light treatment at postharvest stage suppressed the expression of CmPIF8, and released the inhibitory effect of CmPIF8 on CmACO1, thereby promoting the ethylene production and fruit ripening, which indirectly increased the sucrose content in melon fruit.