The plant hormone auxin, typified by indole-3-acetic acid (IAA), regulates various aspects of plant growth and development such as cell division, vascular differentiation, lateral root formation, apical dominance, morphogenesis, oncogenesis, tropisms, and is generally considered to be responsible for regulating plant cell growth. Despite the importance of auxin in plant development, the primary molecular mechanism of auxin action is poorly understood. Experimental evidence accumulated during the past 10 years indicates that the hormone acts rapidly (3-5 min) at the transcriptional level regulating expression of a variety of genes such as Aux/IAAs, SAURs, and GHs. Early auxin-induced Aux/IAA gene expression is mediated in part by the interaction of Aux/IAA proteins with the ARFs (auxin responsive factors). This interaction is regulated by auxin-mediated proteolytic degradation of Aux/IAA proteins. The Aux/IAA proteins are transcription factors that interact with the ARFs and together control a large number of genes involved in a large spectrum of developmental processes regulated by auxin. The specific aims of the proposal are:1. To characterize null mutations for most of the Aux/IAA and ARF gene family members and construct higher order mutations for elucidating the biological function of these proteins. The null mutations will be used for RNA profiling to determine the downstream genes that are regulated by some of the Aux/IAA and ARF gene family members, and for biochemical studies.2. To determine the DNA binding specificities of some ARF gene family members, define the DNA binding domains of ARF1 and ARF6 using a yeast molecular genetic screen, and determine their genomic binding sites with microarray technology.3. To molecularly characterize the recently cloned age1 mutation, a negative regulator of early Aux/IAA gene expression. AGE1 is a homolog of the yeast RAD3 and human XPD/ERCC2 protein, which is a component of the TFIIH transcription factor that participates in nucleotide excision repair (NER) and basal transcription. To clone and characterize the age2 mutation, another negative regulator of the auxin signaling pathway.The elucidation of the primary mechanisrn of auxin action is of paramount importance in Plant Science.