Plant and Cell Physiology Advance Access originally published online on January 30, 2006
Plant and Cell Physiology 2006 47(4):493-503; doi:10.1093/pcp/pcj016
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Isolation and Characterization of a Novel Peroxidase Gene ZPO-C Whose Expression and Function are Closely Associated with Lignification during Tracheary Element Differentiation
1 Department of Biology, Faculty of Science, Ehime University, Matsuyama, 790-8577 Japan
2 RIKEN Plant Science Center, Yokohama, 230-0045 Japan
3 Botanical Gardens, Graduate School of Science, The University of Tokyo, Tokyo, 112-0001 Japan
4 Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo, 113-0033 Japan
* Corresponding author: E-mail, ysato{at}sci.ehime-u.ac.jp; Fax, +81-89-927-9630.
In an attempt to elucidate the regulatory mechanism of vessel lignification, we isolated ZPO-C, a novel peroxidase gene of Zinnia elegans that is expressed specifically in differentiating tracheary elements (TEs). The ZPO-C transcript was shown to accumulate transiently at the time of secondary wall thickening of TEs in xylogenic culture of Zinnia cells. In situ hybridization indicated specific accumulation of the ZPO-C transcript in immature vessels in Zinnia seedlings. Immunohistochemical analysis using anti-ZPO-C antibody showed that the ZPO-C protein is abundant in TEs, especially at their secondary walls. For enzymatic characterization of ZPO-C, 6xHis-tagged ZPO-C was produced in tobacco cultured cells and purified. The ZPO-C:6xHis protein had a peroxidase activity preferring sinapyl alcohol as well as coniferyl alcohol as a substrate, with a narrow pH optimum around 5.25. The peroxidase activity required calcium ion and was elevated by increasing Ca2+ concentration in the range of 0–10 mM. An Arabidopsis homolog of ZPO-C, At5g51890, was examined for expression patterns with transgenic plants carrying a yellow fluorescent protein (YFP) gene under the control of the At5g51890 promoter. The YFP fluorescence localization demonstrated vessel-specific expression of At5g51890 in the Arabidopsis roots. Taken collectively, our results strongly suggest that ZPO-C and its homologs play an important role in lignification of secondary cell walls in differentiating TEs.
The nucleotide sequence reported in this paper has been submitted to DDBJ under accession number AB023959 [GenBank] (ZPO-C).
(Received December 13, 2005; Accepted January 22, 2006)
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