J Integr Plant Biol. ›› 2022, Vol. 64 ›› Issue (1): 5-22.DOI: 10.1111/jipb.13190

• Cell and Developmental Biology • Previous Articles     Next Articles

Growth asymmetry precedes differential auxin response during apical hook initiation in Arabidopsis

Yang Peng1,2,3, Dan Zhang1,2, Yuping Qiu1,2, Zhina Xiao1,2, Yusi Ji1,4, Wenyang Li1,2, Yiji Xia3, Yichuan Wang1,2* and Hongwei Guo1,2*   

  1. 1 Department of Biology, Institute of Plant and Food Science, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
    2 Department of Biology, Key Laboratory of Molecular Design for Plant Cell Factory of Guangdong Higher Education Institutes, School of Life Sciences, Southern University of Science and Technology, Shenzhen 518055, China
    3 Department of Biology, Faculty of Science, Hong Kong Baptist University, Kowloon Tong, Hong Kong 999077, China
    4 Microlens Technologies, Beijing 100086, China

    *Correspondences: Yichuan Wang (wangyc@sustech.edu.cn); Hongwei Guo (guohw@sustech.edu.cn, Dr. Guo is fully responsible for the distributions of all materials associated with this article)
  • Received:2021-10-25 Accepted:2021-11-15 Online:2021-11-16 Published:2022-01-01

Abstract: The development of a hook-like structure at the apical part of the soil-emerging organs has fascinated botanists for centuries, but how it is initiated remains unclear. Here, we demonstrate with high-throughput infrared imaging and 2-D clinostat treatment that, when gravity-induced root bending is absent, apical hook formation still takes place. In such scenarios, hook formation begins with a de novo growth asymmetry at the apical part of a straightly elongating hypocotyl. Remarkably, such de novo asymmetric growth, but not the following hook enlargement, precedes the establishment of a detectable auxin response asymmetry, and is largely independent of auxin biosynthesis, transport and signaling. Moreover, we found that functional cortical microtubule array is essential for the following enlargement of hook curvature. When microtubule array was disrupted by oryzalin, the polar localization of PIN proteins and the formation of an auxin maximum became impaired at the to-be-hook region. Taken together, we propose a more comprehensive model for apical hook initiation, in which the microtubule-dependent polar localization of PINs may mediate the instruction of growth asymmetry that is either stochastically taking place, induced by gravitropic response, or both, to generate a significant auxin gradient that drives the full development of the apical hook.

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