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DEVELOPMENT AND HORMONE ACTION

Developmental Role and Auxin Responsiveness of Class III Homeodomain Leucine Zipper Gene Family Members in Rice^{1,[C],[W],[OA]}

Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113–8657, Japan (J.-I.I., K.-I.H., Y.N.); and Department of Biological Mechanisms and Functions, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464–8601, Japan (Y.S.)

Members of the Class III homeodomain leucine zipper (Class III HD-Zip) gene family are central regulators of crucial aspects of plant development. To better understand the roles of five Class III HD-Zip genes in rice (Oryza sativa) development, we investigated their expression patterns, ectopic expression phenotypes, and auxin responsiveness. Four genes, OSHB1 to OSHB4, were expressed in a localized domain of the shoot apical meristem (SAM), the adaxial cells of leaf primordia, the leaf margins, and the xylem tissue of vascular bundles. In contrast, expression of OSHB5 was observed only in phloem tissue. Plants ectopically expressing microRNA166-resistant versions of the OSHB3 gene exhibited severe defects, including the ectopic production of leaf margins, shoots, and radialized leaves. The treatment of seedlings with auxin quickly induced ectopic OSHB3 expression in the entire region of the SAM, but not in other tissues. Furthermore, this ectopic expression of OSHB3 was correlated with leaf initiation defects. Our findings suggest that rice Class III HD-Zip genes have conserved functions with their homologs in Arabidopsis (Arabidopsis thaliana), but have also acquired specific developmental roles in grasses or monocots. In addition, some Class III HD-Zip genes may regulate the leaf initiation process in the SAM in an auxin-dependent manner.

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: Yasuo Nagato (anagato{at}mail.ecc.u-tokyo.ac.jp).

^[C] Some figures in this article are displayed in color online but in black and white in print.

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.118679

^* Corresponding author; e-mail anagato{at}mail.ecc.u-tokyo.ac.jp.

Received March 4, 2008; accepted June 16, 2008; published June 20, 2008.

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