Journal Article

Two Azuki Bean XTH Genes, <i>VaXTH1</i> and <i>VaXTH2</i>, with Similar Tissue-Specific Expression Profiles, are Differently Regulated by Auxin

Takuma Nakamura, Ryusuke Yokoyama, Etsuko Tomita and Kazuhiko Nishitani

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 1, pages 16-24
Published in print January 2003 | ISSN: 0032-0781
Published online January 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg002
Two Azuki Bean XTH Genes, VaXTH1 and VaXTH2, with Similar Tissue-Specific Expression Profiles, are Differently Regulated by Auxin

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To gain insight into the functional diversity of the XTH (xyloglucan endotransglucosylase/hydrolase) gene family, we analyzed the expression profiles of two azuki bean genes, VaXTH1 and VaXTH2, which share a striking resemblance in their amino acid sequences. The two XTH genes exhibit essentially similar tissue-specific expression profiles, in that both mRNAs are found predominantly in the phloem fibers of growing internodes. However, their expression profiles are not identical. Whereas VaXTH1 is expressed in xylem cells in the basal part of the internode, little or no expression of VaXTH2 is found in the xylem. Furthermore, they exhibit spatially divergent RNA distribution profiles along the internode, VaXTH1 being expressed nearer to the top of the internode than VaXTH2. This indicates their temporally divergent expression profiles during development of the phloem fiber. Indole-3-acetic acid (IAA) up-regulates both of the mRNA levels. However, this effect of IAA on the VaXTH1 gene is nullified in 0.25 M mannitol, which prevents cell expansion without affecting auxin action per se. In contrast, the IAA-induced up-regulation of the VaXTH2 gene is not affected by mannitol. Furthermore, fusicoccin, which promotes acidification and growth, up-regulates VaXTH1 expression, but not VaXTH2 expression. Thus, the two XTH genes are committed to different steps of the cell wall dynamics in the same cell type at different stages of phloem fiber development, and are regulated by IAA in different ways.

Keywords: Keywords: Auxin — Azuki bean — Cell wall — EXGT/XET — Phloem fiber — XTH.; Abbreviations: EXGT, endoxyloglucan transferase; FC, fusicoccin; VaXTH, Vigna angularis XTH; XET, xyloglucan endotransglycosylase; XTH, xyloglucan endotransglucosylase/hydrolase.

Journal Article.  6783 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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