Functional Dissection of a Rice Dr1/DrAp1 Transcriptional Repression Complex

Abstract

We characterized rice cDNA sequences for OsDr1 and OsDrAp1 , which encode structural homologs of the eukaryotic general repressors Dr1 and DrAp1, respectively. OsDr1 and OsDrAp1 are nuclear proteins that interact with each other and with the TATA binding protein/DNA complex. In vitro and in vivo functional analyses showed that OsDrAp1 functions as a repressor, unlike its role in other eukaryotic systems, in which DrAp1 is a corepressor. OsDr1 and OsDrAp1 functioned together as a much stronger repressor than either one alone. Functional dissections revealed that the N-terminal histone-fold domains of OsDr1 and OsDrAp1 were necessary and sufficient for their repression and proteinprotein interaction with each other. The unique glutamine-and proline-rich domain of OsDr1 had no repression activity. The basic amino acid-rich region and an arginine and glycine repeat domain of OsDrAp1 enhanced its repression activity. Thus, although OsDr1 and OsDrAp1 function as repressors, the functions of the two components are reversed compared with those of their nonplant counterparts. INTRODUCTIONSuccessful plant growth, development, and response to environmental cues require precise control of gene expression. A key control stage of differential gene expression is transcriptional regulation mediated by transcriptional factors. Studies of plant transcription factors have focused mainly on activators (Schwechheimer et al., 1998;Riechmann et al., 2000), whereas repressors have just begun to receive attention.Several transcriptional repressors have been cloned from plants, and the elucidation of their functional mechanisms has begun. Transcriptional repressors have been found to mediate plant hormone signal transduction. For example, the soybean G box binding factor 2 (SGBF-2) is a basic leucine zipper (bZIP)-type factor that binds to the G box of the auxin response element of the GH3 promoter and represses both basal and auxin-induced transcription of a reporter gene (Liu et al., 1997). In Arabidopsis, auxin response factor 1 (ARF1) binds to the auxin response element TGTCTC and functions as a repressor (Ulmasov et al., 1999). Arabidopsis ethylene-responsive element binding factors 3 and 4 (AtERF3 and AtERF4) interact with the ethylene-responsive element (GCC box) and repress the basal activity of a reporter gene and the activity of the transcription activator AtERF5 (Fujimoto et al., 2000). Tobacco ERF3 (NtERF3) also functions as a GCC box-dependent transcriptional repressor. The C-terminal 35 amino acids of NtERF3, which contains the conserved L/FDLNL/F(X)P motif, are sufficient to confer the capacity for transcriptional repression on a heterologous DNA binding domain (Ohta et al., 2001). A developmentspecific transcriptional repressor gene, ROM2 , has been cloned from French bean. ROM2 is a bZIP-type transcription factor that functions as a DNA binding site-dependent repressor. ROM2 represses PvALF-activated transcription of the promoter of phytohemagglutinin ( DLEC2 ). The expression analysis indicates that the ROM2 repressor m...

QTL mapping of ten agronomic traits on the soybean (Glycine max L. Merr.) genetic map and their association with EST markers

“…In rice, a homologous protein OsDr1 has been isolated and found to encode a nuclear repressor protein. This protein can interact with another protein, OsDrAp1, and with a TATA binding protein/ DNA complex (Song et al 2002). Further study of GmKF059 should reveal its possible functions in soybean.…”

The NC2 α and β subunits play different roles in vivo

“…For example, sin4 mutation suppresses the lethality of cells lacking NC2 ␤ but not of cells lacking NC2 ␣ (Kim et al 2000). Interestingly, in plants a role for NC2 ␣ without NC2 ␤ has also been described, in that rice NC2 ␣ can function as a repressor independently of NC2 ␤ (Song et al 2002).…”

A Rice WRKY Gene Encodes a Transcriptional Repressor of the Gibberellin Signaling Pathway in Aleurone Cells

“…(3) A repressor can compete with an activator to bind to the same cis-acting element in the promoter (Lodish et al, 2000). (4) A repressor can block assembly of the transcription machinery, as in the cases of Srb10 (Hengartner et al, 1998) and Dr1/ DrAp1-mediated repression (Song et al, 2002). (5) A repressor can promote the degradation of a transcriptional activator, as exemplified in COP1-mediated degradation of HY5 factor (Osterlund et al, 2000).…”