Recent advances with auxin response factors （ARFs）：a review

Auxin response factors （ARFs） are important transcription factors which regulate the expression of auxin response genes in plants and which take on an important role in auxin signal transduction. ARFs can bind specifically to a TGTCTC motif （auxin response element） and mediate auxin responses including activating or inhibiting gene expression. Based on recent advances in the molecular biology of ARFs，structural characteristics as well as biological functions of ARFs and their regulation mechanism are discussed. A typical ARF protein consists of a N-terminal DNA Binding Domain （DBD），a variable middle region that may function as an activation domain （AD） or a repression domain （RD），and one C-terminal Aux/IAA domain （CTD）. ARFs promote the transcription of early genes by combining auxin response elements，and they regulate the expression of downstream genes in the process of auxin signal transduction. Different ARFs are expressed in different tissues and organisms. Also，the study of ARF mutants has indicated that different ARFs possess different functions，which are due to differences in temporal and spatial expression and due to affinities with promoters of target genes. Additionally，plant hormones，environmental factors，and non-coding small RNA act as important functions in regulating ARFs.［Ch，1 fig. 42 ref.］