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First published online November 11, 2005; 10.1104/pp.105.066910 Plant Physiology 139:1704-1716 (2005) © 2005 American Society of Plant Biologists Involvement of a Cell Wall-Associated Kinase, WAKL4, in Arabidopsis Mineral Responses1,[W]Department of Biology (X.H., H.T., J.S., X.P., Z.-H.H.) and Department of Chemistry and Biochemistry (J.D.W.), San Francisco State University, San Francisco, California 94132
The cell wall-associated receptor kinase (WAK) and WAK-like kinase (WAKL) gene family members are good candidates for physical linkers that signal between the cell wall and the cytoplasmic compartment. Previous studies have suggested that while some WAK/WAKL members play a role in bacterial pathogen and heavy-metal aluminum responses, others are involved in cell elongation and plant development. Here, we report a functional role for the WAKL4 gene in Arabidopsis (Arabidopsis thaliana) mineral responses. Confocal microscopic studies localized WAKL4-green fluorescent protein fusion proteins on the cell surfaces suggesting that, like other WAK/WAKL proteins, WAKL4 protein is associated with the cell wall. Histochemical analyses of the WAKL4 promoter fused with the
1 This work was supported by the National Institutes of Health (grant no. MBRS SCORE 5 SO6 GM 52533) and by the National Science Foundation (grant no. MCB 9985135). 2 Present address: Plant Biology Graduate Group, 1002 Life Sciences Addition, University of California, Davis, CA 95616. 3 Present address: Laboratory of Molecular Plant Physiology, South China Agricultural University, Guangzhou 510642, China. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Zheng-Hui He (zhe{at}sfsu.edu). [W] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.066910. * Corresponding author; e-mail zhe{at}sfsu.edu; fax 415–338–2938. Received June 9, 2005; returned for revision July 25, 2005; accepted September 22, 2005. This article has been cited by other articles:
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-glucuronidase reporter gene have shown that WAKL4 expression is induced by Na+, K+, Cu2+, Ni2+, and Zn2+. A transgenic line with a T-DNA insertion at 40-bp upstream of the WAKL4 start codon was characterized. While the T-DNA insertion had little effect on the WAKL4 transcript levels under normal growth conditions, it significantly altered the expression patterns of WAKL4 under various conditions of mineral nutrients. Semiquantitative and quantitative reverse transcription-PCR analyses showed that the promoter impairment abolished WAKL4-induced expression by Na+, K+, Cu2+, and Zn2+, but not by Ni2+. Whereas the WAKL4 promoter impairment resulted in hypersensitivity to K+, Na+, Cu2+, and Zn2+, it conferred a better tolerance to toxic levels of the Ni2+ heavy metal. WAKL4 was required for the up-regulation of zinc transporter genes during zinc deficiency, and the WAKL4 T-DNA insertion resulted in a reduction of Zn2+ accumulation in shoots. A WAKL4-green fluorescent protein fusion gene driven by either the WAKL4 native promoter or the 35S constitutive promoter complemented the phenotypes. Our results suggest versatile roles for WAKL4 in Arabidopsis mineral nutrition responses. 
