AUXIN-REGULATED TRANSCRIPTION

We have cloned and sequenced a number of auxin-responsive cDNAs and their corresponding genes from soybean and Arabidopsis. Each of these genes, with the exception of GH2/4, is transcriptionally regulated specifically by auxins within minutes after hormone application. The auxin-responsive mRNAs are induced some 3-60-fold depending on the type of mRNA analysed, the tissue examined, the dose and duration of auxin application, and the manipulation of the organ tested. Some of the mRNAs show rapid turnover kinetics. The mRNAs show distinct patterns of organ-specific, tissue-specific, and developmental-specific expression. The promoters of the auxin-responsive genes have been fused to the E. coli uidA gene which encodes beta-glucuronidase (GUS) and transferred into tobacco and/or Arabidopsis via Agrobacterium T-DNA. These promoters and parts of these promoters have been used to follow the expression patterns and auxin-inducibility of the reporter genes in transgenic plants. We are attempting to identify minimal auxin-responsive elements and gravity-responsive elements within these promoters. We have also fused the auxin-inducible promoters to bacterial genes that encode cytokinin and auxin biosynthetic or conjugating enzymes to study the effects of organ, tissue, and developmental-specific expression of cytokinins and auxins on plant growth, development, and physiology.