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First published online 23 April 2008
doi: 10.1242/dev.016873

Development 135, 1991-1999 (2008)
Published by The Company of Biologists 2008
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The TTG1-bHLH-MYB complex controls trichome cell fate and patterning through direct targeting of regulatory loci

Mingzhe Zhao1, Kengo Morohashi2, Greg Hatlestad1, Erich Grotewold2 and Alan Lloyd1,*

1 Section of Molecular Cell and Developmental Biology and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, 2500 Speedway, Austin, TX 78712, USA.
2 Department of Plant Cellular and Molecular Biology and Plant Biotechnology Center, The Ohio State University, Columbus, OH 43210, USA.

* Author for correspondence (e-mail: lloyd{at}uts.cc.utexas.edu)

Accepted 4 April 2008

A network of three classes of proteins consisting of bHLH and MYB transcription factors, and a WD40 repeat protein, TRANSPARENT TESTA GLABRA1 (TTG1), act in concert to activate trichome initiation and patterning. Using YFP-TTG1 translational fusions, we show that TTG1 is expressed ubiquitously in Arabidopsis leaves and is preferentially localized in the nuclei of trichomes at all developmental stages. Using a conditional transgenic allele, we demonstrate that TTG1 directly targets the same genes as the bHLH protein GLABRA3 (GL3). In vivo binding of the R2R3-MYB protein GLABRA1 (GL1) to the promoters of GLABRA2 (GL2), TRANSPARENT TESTA GLABRA2 (TTG2), CAPRICE (CPC) and ENHANCER OF TRIPTYCHON AND CAPRICE1 (ETC1) establishes that these genes are major transcriptional targets for the TTG1-bHLH-MYB regulatory complex. By co-precipitation, we confirm that TTG1 associates with GL3 and GL1 in vivo, forming a complex. The loss of TTG1 and GL1 through mutation, affects the subcellular distribution of GL3. Using particle bombardment, we show that TTG1, GL3, GL1 and the homeodomain protein GL2 do not move between adjacent epidermal cells, while the R3-MYB, CPC, does move to neighboring cells. These data support a model for the TTG1 complex directly regulating activators and repressors and the movement of repressors to affect trichome patterning on the Arabidopsis leaf.

Key words: Epidermis, Pattern formation, Trichome, Gene regulation, Cell differentiation, Leaf, Arabidopsis thaliana, Cell fate, Transcription, TTG1


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