Ethylene signaling regulation of freezing tolerance in Arabidopsis
Yiting Shi, Shouwei Tian, Lingyan Hou, Xiaozhen Huang, Xiaoyan Zhang, and ShuhuaYang*

State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
*Corresponding Author：Tel: (+8610)-62734838; Fax: (+8610)-62734838; E-mail: yangshuhua@cau.edu.cn

Abstract
The phytohormone ethylene regulates multiple aspects of plant growth and development and responses to environmental stress. However, the exact role of ethylene in response to freezing stress remains unclear. Here, we show that ethylene negatively regulates plant responses to freezing stress in Arabidopsis. Freezing tolerance was decreased in ethylene overproducer1 mutant and by the application of the ethylene precursor ACC, but increased by the addition of the ethylene biosynthesis inhibitor AVG or the perception antagonist Ag⁺. Furthermore, ethylene insensitive mutants, including etr1-1, ein4-1, ein2-5, ein3-1 and ein3 eil1, displayed enhanced freezing tolerance. In contrast, the constitutive ethylene response mutant ctr1-1 and EIN3-overexpressing plants exhibited reduced freezing tolerance. Genetic and biochemical analyses revealed that EIN3 negatively regulated the expression of CBFs and type-A ARR5, ARR7 and ARR15 by binding to specific elements in their promoters. Overexpression of these ARR genes enhanced the freezing tolerance of plants. Thus, our study demonstrates that ethylene negatively regulates plant freezing tolerance by repressing the cold-regulated CBFs and type-A ARR genes mediated by EIN3/EIL1.

Key Words: ethylene; freezing tolerance; EIN3; CBF; type-A ARR; Arabidopsis