ArabidopsisWUSCHEL Is a Bifunctional Transcription Factor That Acts as a Repressor in Stem Cell Regulation and as an Activator in Floral Patterning

Abstract

Most transcription factors act either as activators or repressors, and no such factors with dual function have been unequivocally identified and characterized in plants. We demonstrate here that the Arabidopsis thaliana protein WUSCHEL (WUS), which regulates the maintenance of stem cell populations in shoot meristems, is a bifunctional transcription factor that acts mainly as a repressor but becomes an activator when involved in the regulation of the AGAMOUS (AG) gene. We show that the WUS box, which is conserved among WOX genes, is the domain that is essential for all the activities of WUS, namely, for regulation of stem cell identity and size of floral meristem. All the known activities of WUS were eliminated by mutation of the WUS box, including the ability of WUS to induce the expression of AG. The mutation of the WUS box was complemented by fusion of an exogenous repression domain, with resultant induction of somatic embryogenesis in roots and expansion of floral meristems as observed upon ectopic expression of WUS. By contrast, fusion of an exogenous activation domain did not result in expanded floral meristems but induced flowers similar to those induced by the ectopic expression of AG. Our results demonstrate that WUS acts mainly as a repressor and that its function changes from that of a repressor to that of an activator in the case of regulation of the expression of AG.

Evolutionarily conserved repressive activity of WOX proteins mediates leaf blade outgrowth and floral organ development in plants

“…2C). Mutation of two amino acids (leucine-to-alanine exchange) in the WUS-box of STF (STFm1), similar to that reported by Ikeda et al (19), partially relieved this repression ( Fig. 2 A-C), suggesting that STF is a transcriptional repressor and that its WUS-box is at least partially responsible for mediating the repressive activity.…”

Regulatory modules controlling maize inflorescence architecture

“…Previous work showed that RA1's two EAR motifs interact with a protein encoded by ramosa enhancer locus2, an ortholog of the corepressor TOPLESS (Gallavotti et al 2010). While EAR motifs may confer repressive activity to TFs (Kagale and Rozwadowski 2011), there are examples where transcriptional repressors, such as the stem cell regulator WUSCHEL, activate gene expression in specific developmental contexts (Ikeda et al 2009). Activated and repressed targets of RA1 were partitioned both developmentally and temporally, suggesting the mechanism of RA1 action depends on spatiotemporal context.…”

Type-B ARABIDOPSIS RESPONSE REGULATORs Specify the Shoot Stem Cell Niche by Dual Regulation of WUSCHEL

“…Our data show that ARR1, ARR10, and ARR12 exhibit dual functions in transcription regulation and activate the transcription of WUS and repress that of YUCs within the same cell niche. WUS has previously been shown to have a similar dual function (Ikeda et al, 2009). It is possible that different partner proteins interacting with ARRs confer their functions as either transcriptional activators or repressors.…”