The Arabidopsis transcription factor bZIP11 activates auxin-mediated transcription by recruiting the histone acetylation machinery

In higher plants, the hormone auxin orchestrates a diverse array of developmental and environmental responses mainly exerted via transcriptional control. In its absence, auxin-mediated transcription is postulated to be repressed by histone deacetylases, which convert chromatin into a highly packed inactive state. Here we present a converse mechanism where Arabidopsis bZIP11-related basic leucine zipper (bZIP) transcription factors interact via an amino-terminal activation domain with ADA2b adapter proteins to recruit the histone acetylation machinery to specific auxin-responsive genes. Gain, loss-of-function and pharmacological approaches as well as chromatin immunoprecipitation experiments addressing various components of the recruitment and acetylation machinery substantiate the proposed mechanism. Importantly, G-box-related cis -elements, frequently found in auxin-induced promoters, are shown to bind bZIP11-related bZIPs and to function as quantitative modulators of auxin-induced transcription. In conclusion, we describe a regulatory activation mechanism that serves as a rheostat to modulate auxin-mediated responses. Histone acetylation has been proposed to be crucial for the regulation of gene transcription controlled by the plant hormone auxin. Here, the authors show that the bZIP11 transcription factor activates auxin-mediated transcription by recruiting the histone acetylation machinery.