AtWNK9 regulates root elongation and is involved in ABA response in Arabidopsis 
Minmin Xie¹, Reqing He¹, Guifang Duan¹, Qiuhong Duan¹, Jianzhong Lin¹, Dongying Tang¹, Xiaoying Zhao¹*, Xuanming Liu^1,2

¹Bioenergy and Biomaterial Research Center, College of Biology, Hunan University, Changsha 410082.
²State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha 410082.
*Corresponding author:Tel: (+86731)88664048; Email: zxy_mm@163.com

Abstract 
AtWNK9 (with no lysine kinase) protein kinase gene is root-specific expressed in Arabidopsis, but its function remains unknown. Here we report that wnk9 mutant showed shorter primary root, while the over-expression lines of WNK9 had longer primary root compared with wild type plants. The mRNA expression of WNK9 was induced by ABA. When grown in the presence of ABA the seedlings exhibited ABA-inhibited root elongation, and the WNK9 over-expression lines showed hypersensitivity to ABA, however wnk9 mutant showed lower sensitivity to ABA compared with wild type seedlings. Moreover, the WNK9 over-expression lines exhibited decreased stomatal open, lower water-loss rate, more proline accumulation compared with wild type in response to ABA, while reverse phenotype was showed in the wnk9 mutant. Q-PCR results showed that a series of ABA-responsive genes were induced by ABA, and their expression level was lower in the wnk9 mutant but higher in the over-expression lines than that in the wild type. Subcellular localization result showed that WNK9 localizes in cell membrane. These results indicate that WNK9 might regulate root elongation through ABA signal transduction.

Key words: AtWNK9, Root elongation, ABA, Arabidopsis