Activation of gibberellin 20-oxidase 2 undermines auxin-dependent root and root hair growth in NaCl-stressed Arabidopsis seedlings
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Although salt stress mainly disturbs plant root growth by affecting the biosynthesis and signaling of phytohormones, such as gibberellin (GA) and auxin, the exact mechanisms of the crosstalk between these two hormones remain to be clarified. Indole-3-acetic acid (IAA) is a biologically active auxin molecule. In this study, we investigated the role of Arabidopsis GA20-oxidase 2 (GA20ox2), a final rate-limiting enzyme of active GA biosynthesis, in IAA-directed root growth under NaCl stress. Under the NaCl treatment, seedlings of a loss-of-function ga20ox2-1 mutant exhibited primary root and root hair elongation, altered GA4 accumulation, and decreased root Na+ contents compared with the wild-type, transgenic GA20ox2-complementing, and GA20ox2-overexpression plant lines. Concurrently, ga20ox2-1 alleviated the tissue-specific inhibition of NaCl on IAA generation by YUCCAs, IAA transport by PIN1 and PIN2, and IAA accumulation in roots, thereby explaining how NaCl increased GA20ox2 expression in shoots but disrupted primary root and root hair growth in wild-type seedlings. In addition, a loss-of-function pin2 mutant impeded GA20ox2 expression, indicating that GA20ox2 function requires PIN2 activity. Thus, the activation of GA20ox2 retards IAA-directed primary root and root hair growth in response to NaCl stress.
KeywordsGA20ox2 NaCl IAA PIN1/2 Primary root or root hair length
We thank Dr. Jian Xu (National University of Singapore, Singapore) for providing PIN2-GFP and DR5-GUS seeds. This work was supported by funding from the National Natural Science Foundation of China to Jing Jiang (Grant Numbers 30971509 and 31271510). We thank Lesley Benyon, PhD, from Liwen Bianji, Edanz Group China (http://www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.
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