Transcriptional repression of target genes by LEUNIG and SEUSS, two interacting regulatory proteins for Arabidopsis flower development

doi:10.1073/pnas.0403055101

Transcriptional repression of target genes by LEUNIG and SEUSS, two interacting regulatory proteins for Arabidopsis flower development

^*Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742; and ^†School of Biological Sciences, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP, United Kingdom

Edited by Michael F. Thomashow, Michigan State University, East Lansing, MI, and approved June 22, 2004 (received for review May 3, 2004)

Abstract

Transcription repression plays important roles in preventing crucial regulatory proteins from being expressed in inappropriate temporal or spatial domains. LEUNIG (LUG) and SEUSS (SEU) normally act to prevent ectopic expression of the floral homeotic gene AGAMOUS in flowers. LUG encodes a protein with sequence similarities to the yeast Tup1 corepressor. SEU encodes a plant-specific regulatory protein with sequence similarity in a conserved dimerization domain to the LIM-domain binding 1/Chip proteins in mouse and Drosophila. Despite the molecular isolation of LUG and SEU, the biochemical function of these two proteins remains uncharacterized, and the mechanism of AGAMOUS repression remains unknown. Here, we report that LUG and SEU interact directly in vitro and in vivo. Furthermore, LUG exhibits a strong repressor activity on several heterologous promoters in yeast and plant cells. SEU, in contrast, does not exhibit any direct repressor activity, but can repress reporter gene expression only in the presence of LUG, indicating a possible role of SEU as an adaptor protein for LUG. Our results demonstrate that LUG encodes a functional homologue of Tup1 and that SEU may function similarly to Ssn6, an adaptor protein of Tup1. We have defined the LUG/LUH, Flo8, single-strand DNA-binding protein domain of LUG as both necessary and sufficient for the interaction with SEU and two domains of LUG as important for its repressor function. Our work provides functional insights into plant transcriptional corepressors and reveals both conservation and distinctions between plant corepressors and those of yeast and animals.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: zl17{at}umail.umd.edu.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: LUG, LEUNIG; SEU, SEUSS; AG, AGAMOUS; SSDP, single-strand DNA-binding protein; LUFS, LUG/LUH, Flo8, SSDP; Ldb1, LIM domain-binding 1; Q, glutamine; Gro, Groucho; TLE, transducin-like enhancer of split; TSA, trichostatin-A; HDAC, histone deacetylase; MBP, maltose-binding protein; GAL4BD, DNA-binding domain of GAL4; GAL4AD, activation domain of GAL4; LUC, luciferase; β-gal, β-galactosidase.