Recently, the Protected Cultivation Research Team of the Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, has made significant progress in understanding the mechanism by which hydrogen peroxide (H₂O₂) regulates the opening/closure and growth of cucumber cotyledons. The study reveals that the CsBZR4-CsRBOH5.1-BR module regulates cucumber cotyledon opening/closure and expansion. The related findings have been published in theInternational Journal of Biological Macromolecules(IF=8.5) under the title “CsBZR4-CsRBOH5.1-BR module regulates opening/closure and expansion of cucumber cotyledons.”

Cucumber (Cucumis sativus L.) is a nutrient-rich and widely cultivated vegetable crop. As the initial organ of plant development, cotyledons play a critical role in adapting to the external environment and sustaining life activities. Therefore, studying the growth and development of cucumber cotyledons is of great significance for cultivating robust plants. H₂O₂ plays an important role in various physiological processes in plants. However, its regulatory function and underlying mechanisms in the opening/closure and expansion of cotyledons have not been previously reported.

This study provides the first evidence in plants that H₂O₂ generated through RBOH-mediated pathways serves as a key factor regulating the opening/closure and expansion of cotyledons. Csrboh5.1 mutants, which lack H₂O₂ synthesis, failed to open their cotyledons normally during the day or close them at night, whereas exogenous application of H₂O₂ restored the normal phenotype. Further mechanistic studies revealedthat CsRBOH5.1-H₂O₂ participates in this process by regulating brassinosteroid (BR) synthesis, and BR, in turn, promotes the transcription of CsRBOH5.1 by activating the transcription factor CsBZR4. Notably, CsBZR4 does not directly function as a core signaling component regulating cotyledon opening/closure but indirectly influences the process by transcriptionally regulating CsRBOH5.1.

In summary, this study uncovers for the first time the regulatory role of RBOH-mediated H₂O₂ in cotyledon development and elucidates a novel “CsBZR4-CsRBOH5.1-BR” feedback pathway. This module ensures precise control of cotyledon growth dynamics through the mutual regulation of oxidative metabolism and BR synthesis, providing new insights into the integration of redox homeostasis and hormonal regulation during plant organogenesis.

Fig. 1 The CsBZR4-CsRBOH5.1-BR module regulates opening and closure of cucumber cotyledons

This study was primarily conducted at the Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences.Postdoctoral researcher Liu Lu is the first author, Researcher Li Yansu and Associate Researcher Sun Mintao are the corresponding authors. This research was supported by the National Natural Science Foundation of China (32102462 and 32072652), the Agricultural Science and Technology Innovation Program of the Chinese Academy of Agricultural Sciences (CAAS-ASTIP-IVFCAAS), and the Key Laboratory of Biology and Genetic Improvement of Horticultural Crops, Ministry of Agriculture. Professor Yu Xianchang provided guidance on the experimental design, and Dr. Di Qinghua (now at the Anhui Academy of Agricultural Sciences) created the transgenic materials required for the study.

Link to the article:https://doi.org/10.1016/j.ijbiomac.2025.149186