THE ARF FAMILY OF TRANSCRIPTION FACTORS AND THEIR ROLE IN PLANT HORMONE-RESPONSIVE TRANSCRIPTION

Auxin response factors or ARFs are a recently discovered family of tra nscription factors that bind with specificity to auxin response elemen ts (AuxREs) in promoters of primary or early auxin-responsive genes. A RFs have an amino-terminal DNA-binding domain related to the carboxyl- terminal DNA-binding domain in the maize transactivator VIVIPAROUS1. A ll but one ARF identified to date contain a carboxyl-terminal protein- protein interaction domain that forms a putative amphipathic alpha-hel ix. A similar carboxyl-terminal protein-protein interaction domain is found in the Aux/IAA class of auxin-inducible proteins. Some ARFs cont ain transcriptional activation domains, while others contain repressio n domains. ARFs appear to play a pivotal role in auxin-regulated gene expression of primary response genes.