The plant hormone auxin regulates organ initiation, growth, and development. The Auxin Response transcription Factors (ARFs) mediate transcriptional responses to auxin. Under low auxin concentration, the ARF proteins bind Aux/IAA proteins, which inhibit transcription. As auxin concentration is elevated, Aux/IAA proteins are rapidly degraded, thus allowing ARFs to activate target genes. Two closely related ARF genes, ARF6 and ARF8, regulate flower maturation by promoting stamen elongation and gynoecium development. ARF6 and ARF8 are cleavage targets of plant microRNA, miR167. Phenotypes and transcript expression patterns of miR167-insensitive mARF6 and mARF8 transgenic plants showed that miR167 patterns ARF6 and ARF8 transcript distribution in the ovule and in the anther, and this patterning activity is important for development of these two organs. Silencing ARF6 and ARF8 in the style and in the ovule funiculus by expressing a miR167 precursor gene, MIR167a, further showed that ARF6 and ARF8 promote stigmatic papillae elongation and pollen tube growth in these two different floral tissues. To further reveal functions of other ARF genes in flowers, especially during ovule formation, we repressed activity of ARF proteins by expressing a gain-of-function aux/iaa gene in the ovule outer integument and in the funiculus. We found that auxin response in the ovule is important for the asymmetric growth of the outer integument and for differentiation of the entire ovule. These results showed that auxin and the ARF-mediated auxin responses regulate multiple aspects of flower development.