Figure 8. An auxin triggered chromatin state switch.
(A) In conditions of low auxin, Aux/IAA proteins bind to MP transcription factor associated with target loci and prevent gene expression in two ways: by recruiting the co-repressor TOPLESS (TPL) and histone deacetylase HDA19 and by preventing recruitment of the BRM or SYD chromatin remodeling complexes. (B) Upon establishment of a local auxin maximum, Aux/IAA proteins are degraded, this leads to eviction of HDA19 and TPL. Aux/IAA degradation also frees MP to recruit BRM or SYD complexes. The chromatin remodeling complexes open up the compacted chromatin by reducing nucleosome occupancy, thus increasing the accessibility of the genomic DNA near MP bound sites. (C) The ‘chromatin unlocking’ allows additional transcription factors access to their cis elements. This, possibly via additional steps, leads to recruitment of the general transcriptional machinery and initiation of transcription. HAT: histone acetyl transferase. GRE: binding site for transcription factor (TF). Figure 8—figure supplement 1 shows evolutionarily conserved cis elements near the midpoint of the well-positioned nucleosome at the FIL locus.
Figure 8—figure supplement 1. Two evolutionarily conserved cis elements close to the midpoint of the well-positioned nucleosome at the FIL locus.
