Fruit color transformation involves chlorophyll degradation, a key process determining ripening quality. Ethylene is known to trigger chlorophyll breakdown, while light can either promote synthesis or degradation depending on conditions. In apple fruit, exposure to strong light often accelerates color loss compared with darkness, suggesting a synergistic role between light and ethylene signaling. However, the mechanisms coordinating these cues remain largely unknown. Although prior studies identified MdERF17 as a downstream regulator of ethylene-induced chlorophyll degradation, how light signaling factors contribute to this network has been unclear. Due to these challenges, it is necessary to explore how transcription factors integrate light and ethylene signals to regulate chlorophyll degradation.
Researchers from Shandong Agricultural University have unveiled how two key transcription factors—MdEIL1 and MdHY5—bridge ethylene and light signaling to promote chlorophyll degradation in apple peels. The study (DOI: 10.1093/hr/uhae324), published on March 1, 2025, in Horticulture Research, demonstrates that these factors cooperate to activate downstream chlorophyll degradation genes and accelerate peel color change during fruit ripening. Through physiological assays, gene expression profiling, and protein interaction experiments, the team established a mechanistic model in which ethylene and light jointly regulate apple degreening via the MdEIL1–MdHY5–MdERF17 signaling pathway.
The team treated mature ‘Golden Delicious’ apples with ethylene and its inhibitor (1-MCP) under light and dark conditions. Ethylene accelerated chlorophyll loss, which was further enhanced by light exposure, confirming additive effects of both signals. Expression analyses revealed that ethylene induced MdEIL1, light activated MdHY5, and both jointly elevated MdERF17 expression. Functional assays showed that overexpressing MdEIL1 or MdHY5 decreased chlorophyll content, whereas silencing them delayed peel degreening.
Molecular experiments, including yeast one-hybrid, electrophoretic mobility shift assays (EMSA), chromatin immunoprecipitation (ChIP-qPCR), and luciferase reporter analyses, demonstrated that MdEIL1 binds to the promoters of MdHY5 and MdERF17, while MdHY5 binds to the MdERF17 promoter. Moreover, the MdEIL1–MdHY5 protein complex enhanced transcriptional activation of these genes. Co-overexpression of MdEIL1 and MdHY5 caused the most significant chlorophyll reduction in apple peels, highlighting their synergistic role. The study proposes a regulatory model in which light promotes ethylene biosynthesis, ethylene activates MdEIL1, and light activates MdHY5; together they form a feedback module that induces MdERF17 and downstream degradation genes (MdPPH, MdNYC1), accelerating the loss of green color.
“Fruit coloration is one of the most visible indicators of ripening and market readiness,” said corresponding author Prof. Shou-Qian Feng. “Our research shows that light and ethylene do not act independently but communicate through MdEIL1 and MdHY5 to fine-tune chlorophyll degradation. This discovery deepens our understanding of how external and internal cues integrate to regulate fruit ripening. The MdEIL1–MdHY5 interaction represents a critical control point that can be targeted to adjust fruit appearance, potentially improving breeding and storage practices for apple and other fruit crops.”
Understanding how light and ethylene jointly control peel degreening offers new possibilities for managing fruit coloration and postharvest quality. The MdEIL1–MdHY5 regulatory module provides a molecular basis for developing strategies to manipulate ripening speed and color development under varying storage or environmental conditions. By modulating light exposure or ethylene treatment, growers may better control uniform color transitions, enhancing fruit appearance and market value. Beyond apples, these findings could inform breeding programs in other horticultural crops where color uniformity and shelf appeal depend on tightly coordinated chlorophyll degradation and pigment accumulation.
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References
DOI
10.1093/hr/uhae324
Original Source URL
https://doi.org/10.1093/hr/uhae324
Funding information
This work was supported by the National Key Research and Development Program of China (2023YFD230100, 2018YFD1000105), the National Natural Science Foundation of China (31872940).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.