Intronic regulatory elements determine the divergent expression patterns of AGAMOUS-LIKE6 subfamily members in Arabidopsis

Authors

  • Stephen E. Schauer,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    Search for more papers by this author
  • Philipp M. Schlüter,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    Search for more papers by this author
  • Ramarmurthy Baskar,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    2. Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
    Search for more papers by this author
    • Present address: Department of Biotechnology, Indian Institute of Technology-Madras, Chennai-600 036, India.

  • Jacqueline Gheyselinck,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    Search for more papers by this author
    • Present address: Département de Biologie Moléculaire Végétale, Bâtiment Biophore, Université de Lausanne, CH-1015 Lausanne, Switzerland.

  • Arturo Bolaños,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    Search for more papers by this author
  • Mark D. Curtis,

    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    Search for more papers by this author
  • Ueli Grossniklaus

    Corresponding author
    1. Institute of Plant Biology & Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland
    2. Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA
    Search for more papers by this author

*(fax +41 44 634 8204; e-mail grossnik@botinst.uzh.ch).

Summary

The screening of enhancer detector lines in Arabidopsis thaliana has identified genes that are specifically expressed in the sporophytic tissue of the ovule. One such gene is the MADS-domain transcription factor AGAMOUS-LIKE6 (AGL6), which is expressed asymmetrically in the endothelial layer of the ovule, adjacent to the developing haploid female gametophyte. Transcription of AGL6 is regulated at multiple stages of development by enhancer and silencer elements located in both the upstream regulatory region and the large first intron. These include a bipartite enhancer, which requires elements in both the upstream regulatory region and the first intron, active in the endothelium. Transcription of the AGL13 locus, which encodes the other member of the AGL6 subfamily in Arabidopsis, is also regulated by elements located in the upstream regulatory region and in the first intron. There is, however, no overlapping expression of AGL6 and AGL13 except in the chalaza of the developing ovule, as was shown using a dual gene reporter system. Phylogenetic shadowing of the first intron of AGL6 and AGL13 homologs from other Brassicaceae identified four regions of conservation that probably contain the binding sites of transcriptional regulators, three of which are conserved outside Brassicaceae. Further phylogenetic analysis using the protein-encoding domains of AGL6 and AGL13 revealed that the MADS DNA-binding domain shows considerable divergence. Together, these results suggest that AGL6 and AGL13 show signs of subfunctionalization, with divergent expression patterns, regulatory sequences and possibly functions.

Ancillary