J Integr Plant Biol.

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The transcription factor CsbHLH60 relieves high‐temperature inhibition of chlorophyll degradation in citrus

Zhehui Zhang1, Yongjun Hu1, Ming Wang1, Ziyi Lei1, Shengcai Liao2, Liping Li2, Xiongjie Zheng1,3, Kaijie Zhu1, Lijun Chai1,3, Junli Ye1 and Xiuxin Deng1,3*   

  1. 1. National Key Laboratory for Germplasm Innovation & Utilization of Horticultural Crops, Huazhong Agricultural University, Wuhan 430070, China
    2. Zigui County Fruit and Tea Industry Development Center, Yichang 443600, China
    3. Hubei Hongshan Laboratory, Wuhan 430070, China
    *Correspondence: Xiuxin Den (xxdeng@mail.hzau.edu.cn)
  • Received:2025-08-04 Accepted:2026-04-29 Online:2026-05-25
  • Supported by:
    This work was supported by the Hubei Province Central Guiding Local Science and Technology Development Special Project (2024EIA029) and the China Agriculture Research System of MOF and MARA (CARS‐26).

Abstract: Rising global temperature threatens fruit quality. As one of the most economically valuable fruits worldwide, citrus suffers from high-temperature-induced chlorophyll retention during ripening, significantly reducing commercial value. Comparative physiological analyses revealed that citrus fruit stored at 30°C exhibited markedly impaired chlorophyll degradation and failed to undergo normal degreening, in stark contrast to those maintained at 20°C. This temperature-dependent suppression of degreening was closely associated with a significant downregulation of key chlorophyll catabolic genes (CCGs). By integrating weighted gene co-expression network analysis (WGCNA) of a stay-green mutant, we identified the transcription factor CsbHLH60, a nuclear-localized transcriptional activator, from a chlorophyll-associated module. CsbHLH60 directly binds E-box motifs in the promoters of CsSGR and CsRCCR to drive their expression, a finding validated by ChIP-qPCR and EMSA assays. Transient overexpression of CsbHLH60 in citrus peel accelerated chlorophyll degradation and, importantly, overcame high-temperature-induced repression to restore degreening, whereas RNAi-mediated silencing at 20°C significantly impeded normal degreening of the peel. Mechanistically, high temperature imposes a dual “double-lock” suppression on CsbHLH60, concurrently repressing its transcription and promoting its protein degradation, thereby depleting functional activator levels. Collectively, our findings establish CsbHLH60 as a pivotal temperature-responsive regulator that directly couples temperature signaling to chlorophyll catabolism and is capable of overriding the high-temperature-induced suppression of chlorophyll degradation, thereby highlighting its potential as a molecular target for mitigating climate-driven declines in citrus fruit appearance quality.

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