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DEVELOPMENT AND HORMONE ACTION

Specificity and Similarity of Functions of the Aux/IAA Genes in Auxin Signaling of Arabidopsis Revealed by Promoter-Exchange Experiments among MSG2/IAA19, AXR2/IAA7, and SLR/IAA14^1,[C],[OA]

Department of Biological Sciences, Faculty of Science (H.M., M.K.W., K.T.Y.), and Division of Biological Sciences, Graduate School of Science (M.K.W., D.N., K.T.Y.), Hokkaido University, Sapporo 060–0810, Japan; and Laboratory of Supramolecular Biophysics, Research Institute for Electronic Science, Hokkaido University, Sapporo 060–0812, Japan (M.K.)

As indicated by various and some overlapped phenotypes of the dominant mutants, the Aux/IAA genes of Arabidopsis (Arabidopsis thaliana) concomitantly exhibit a functional similarity and differentiation. To evaluate the contributions of their expression patterns determined by promoter activity and molecular properties of their gene products to Aux/IAA function, we examined phenotypes of transgenic plants expressing the green fluorescent protein (GFP)-tagged msg2-1/iaa19, axr2-1/iaa7, or slr-1/iaa14 cDNA by the MSG2 or AXR2 promoter. When driven by the MSG2 promoter (pMSG2), each GFP-tagged cDNA caused the msg2-1 phenotype, that is, the wild-type stature in the mature-plant stage, long and straight hypocotyls in the dark, reduced lateral root formation, relatively mild agravitropic traits in hypocotyls, and a normal gravitropic response in roots. However, development of one or two cotyledonary primordia was often arrested in embryogenesis of the pMSG2::axr2-1::GFP and pMSG2::slr-1::GFP plants, resulting in monocotyledonary or no cotyledonary seedlings. Such defects in embryogenesis were never seen in pMSG2::msg2-1::GFP or the msg2-1, axr2-1, or slr-1 mutant. The MSG2 promoter-GUS staining showed that expression of MSG2 started specifically in cotyledonary primordia of the triangular-stage embryos. When driven by the AXR2 promoter (pAXR2), each GFP-tagged mutant cDNA caused, in principle, aberrant aboveground phenotypes of the corresponding dominant mutant. However, either the axr2-1::GFP or slr-1::GFP cDNA brought about dwarf, agravitropic stems almost identical to those of axr2-1, and the pAXR2::msg2-1::GFP and pAXR2::slr-1::GFP hypocotyls exhibited complete loss of gravitropism as did axr2-1. These results showed functional differences among the msg2-1, axr2-1, and slr-1 proteins, though some phenotypes were determined by the promoter activity.

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: Hideki Muto (h-muto{at}imd.es.hokudai.ac.jp).

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

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.096628

^* Corresponding author; e-mail h-muto{at}imd.es.hokudai.ac.jp; fax 81–11–706–2739.

Received January 26, 2007; accepted March 13, 2007; published March 16, 2007.