Arabidopsis HB52 mediates the crosstalk between ethylene and auxin by transcriptionally modulating PIN2, WAG1, and WAG2 during primary root elongation

First author: Zi-Qing Miao; Affiliations: University of Science and Technology of China (中国科学技术大学): Anhui, China 

Corresponding author: Chengbin Xiang (向成斌)

The gaseous (气态的) hormone ethylene participates in many physiological processes in plants. Ethylene-inhibited root elongation involves PIN-FORMED2 (PIN2)-mediated basipetal (向基的) auxin transport, but the molecular mechanisms underlying the regulation of PIN2 function by ethylene (and therefore auxin distribution) are poorly understood. Here, we report that the plant-specific and ethylene-responsive HD-Zip gene HB52 is involved in ethylene-mediated inhibition of primary root elongation in Arabidopsis thaliana. Biochemical and genetic analyses demonstrated that HB52 is ethylene responsive and acts downstream of ETHYLENE-INSENSITIVE3 (EIN3). HB52 knockdown mutants displayed an ethylene-insensitive phenotype during primary root elongation, while its overexpression resulted in short roots, as observed in ethylene-treated plants. In addition, root auxin distribution and gravitropism (向重力性) were impaired in HB52 knockdown and overexpression lines. Consistent with these findings, in vitro and in vivo binding experiments showed that HB52 regulates the expression of auxin transport-related genes, including PIN2, WAVY ROOT GROWTH1 (WAG1), and WAG2 by physically binding to their promoter regions. These findings suggest that HB52 functions in the ethylene-mediated inhibition of root elongation by modulating the expression of auxin transport components downstream of EIN3, revealing a mechanism in which HB52 acts as an important node in the crosstalk between ethylene and auxin signaling during plant growth and development.

气态植物激素乙烯参与了植物中很多的生理过程。乙烯抑制植物根的伸长涉及到了PIN2介导的生长素在植物中由上而下的转运，但乙烯调控PIN2的分子机制还不清楚。本文报道了植物特异性乙烯受体HD-Zip基因HB52参与了拟南芥中由乙烯介导的主根伸长抑制。生化和遗传学的试验均显示HB52响应乙烯，并作为EIN3基因的下游发挥作用。HB52敲除突变体在主根伸长方面显示出对乙烯不敏感的表型，而HB52过表达则会出现更长变短的表型，与野生型拟南芥受到乙烯处理时的表型一致。另外，根的生长素分布和向重力性在HB52敲除和过表达突变体中均受损。此外，体内与体外的结合试验显示HB52能够直接结合到PIN2、WAG1和WAG2等生长素转运相关基因的启动区，以调控这些基因的表达。本文的研究揭示了HB52作为EIN3下游因子通过调控生长素转运蛋白的表达在由乙烯介导的根伸长抑制中发挥作用，说明了HB52在植物生长和发育过程中协调乙烯和生长素信号具有非常重要作用。

通讯：向成斌（https://biox.ustc.edu.cn/2010/0626/c692a340117/page.htm）

个人简介：1982年，西南农业大学，园艺系学士；1987年，加州大学河边分校，植物科学系硕士；1992年，爱达荷大学，微生物、生物化学及分子生物学系博士。

研究方向：植物环境胁迫生物学。目前研究内容包括植物耐逆分子机制；耐逆基因资源的发掘与应用；植物氮、硫分子营养；根系构型对环境的适应等。

doi: https://doi.org/10.1105/tpc.18.00584

Journal: Plant Cell

First Published: 17 October, 2018

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