Asymmetric distribution of cytokinins determines root hydrotropism in Arabidopsis thaliana

First author: Jinke Chang; Affiliations: Lanzhou University (兰州大学): Lanzhou, China

Corresponding author: Jia Li 

The phenomenon of plant root tips sensing moisture gradient in soil and growing towards higher water potential is designated as root hydrotropism, which is critical for plants to survive when water is a limited factor. Molecular mechanisms regulating such a fundamental process, however, are largely unknown. Here we report our identification that cytokinins are key signaling molecules directing root growth orientation in a hydrostimulation (moisture gradient) condition. Lower water potential side of the root tip shows more cytokinin response relative to the higher water potential side. Consequently, two cytokinin downstream type-A response regulators, ARR16 and ARR17, were found to be up-regulated at the lower water potential side, causing increased cell division in the meristem zone, which allows the root to bend towards higher water potential side. Genetic analyses indicated that various cytokinin biosynthesis and signaling mutants, including the arr16 arr17 double mutant, are significantly less responsive to hydrostimulation. Consistently, treatments with chemical inhibitors interfering with either cytokinin biosynthesis or cell division completely abolished root hydrotropic response. Asymmetrically induced expression of ARR16 or ARR17 effectively led to root bending in both wild-type and miz1, a previously known hydrotropism-defective mutant. These data demonstrate that asymmetric cytokinin distribution is a primary determinant governing root hydrotropism.

植物根尖感应土壤中水分梯度的以及朝向更高水势生长的现象被称为根的向水性，这对于植物在水分稀缺环境条件下的生存至关重要。调控这类生物进程的分子机制在很大程度上都还不清楚。本文中，作者鉴定了细胞分裂素作为关键的信号分子直接决定了植物根在水分梯度环境下的生长方向。相比于更高水势的一侧，低水势一侧的根尖会显示出更多的细胞分裂素响应。因此，两个细胞分裂素下游A类响应调控因子ARR16/17会在低水势一侧的根尖部位上调表达，从而导致分生组织区的细胞分裂增加，最终根朝向更高水势一侧弯曲。遗传分析显示包括arr16 arr17双突变体在内的多个细胞分裂素生物合成和信号转导突变体均表现出对于水分梯度更少的响应。与此一致的是，外施能够干扰细胞分裂素合成或细胞分裂的化学抑制剂会完全废除根的亲水性响应。不对称的ARR16/17诱导表达有效导致了野生型和miz1突变体的根的弯曲，而miz1突变体是已知的亲水性缺陷突变体。本文的研究结果揭示了不对称的细胞分裂素分布是决定根向水性的主要因素。

通讯：黎家 (http://lifesc.lzu.edu.cn/content-267-1.html)

个人简介：1984年，兰州大学，学士；1989年，中国科学院植物研究所，硕士；1995年，美国弗吉尼亚理工大学，博士；1997-2002年，美国密苏里大学哥伦比亚分校；博士后。

研究方向：1. 油菜素内酯的信号传递、合成、及代谢途径的分子调控机制；2. 拟南芥类受体蛋白激酶的生物学功能；3. 类受体激酶介导的植物细胞凋亡的分子机理。

doi: https://doi.org/10.1038/s41422-019-0239-3

Journal: Cell Research

Published date: October 10, 2019