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Cytokinin regulates the apical hook development via the coordinated actions of EIN3/EIL1 and PIFs in Arabidopsis
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  • Yalikunjiang Aizezi,
  • Huazhang Shu,
  • Linlin Zhang,
  • Hongming Zhao,
  • Yang Peng,
  • Hongxia Lan,
  • Yinpeng Xie,
  • Jian Li,
  • Yichuan Wang,
  • Hongwei Guo,
  • Kai Jiang
Yalikunjiang Aizezi
Institute of Plant and Food Science
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Huazhang Shu
Institute of Plant and Food Science
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Linlin Zhang
Institute of Plant and Food Science
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Hongming Zhao
Institute of Plant and Food Science
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Yang Peng
Institute of Plant and Food Science
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Hongxia Lan
Institute of Plant and Food Science
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Yinpeng Xie
Institute of Plant and Food Science
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Jian Li
Institute of Plant and Food Science
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Yichuan Wang
Institute of Plant and Food Science
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Hongwei Guo
Institute of Plant and Food Science
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Kai Jiang
Institute of Plant and Food Science

Corresponding Author:[email protected]

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Abstract

The apical hook is indispensable for protecting the delicate shoot apical meristem while dicot seedlings emerging from soil after germination in darkness. The development of apical hook is coordinately regulated by multiple phytohormones and environmental factors. Yet, a holistic understanding of the spatial-temporal interactions between different phytohormones and environmental factors remains to be achieved. By a chemical genetics method, we identified kinetin riboside, as a proxy of kinetin, that promotes apical hook development of Arabidopsis thaliana in a partially ethylene-signaling independent pathway. Further genetic and biochemical analysis revealed that cytokinin is able to regulate apical hook development via post-transcriptional regulation of the PHYTOCHROME INTERACTING FACTORs (PIFs), together with its canonical roles in inducing ethylene biosynthesis. Dynamic observations of apical hook development processes showed that ETHYLENE INSENSITVE3 (EIN3) and EIN3-LIKE1 (EIL1) are necessary for the exaggeration of hook curvature in response to cytokinin, while PIFs are crucial for the cytokinin-induced maintenance of hook curvature in darkness. Furthermore, these two families of transcription factors display divergent roles in light-triggered hook opening. Our findings unveil that cytokinin integrates ethylene signaling and light signaling via EIN3/EIL1 and PIFs, respectively, to dynamically regulate apical hook development during early seedling development.