Abstract
Although two predominant forms of endogenous auxins, Indole-3-acetic acid (IAA), and Indole-3-butyric acid (IBA) are produced by the plant, the majority of the research to date is focused on IAA, assuming that IBA acts via IAA pathways. However, IBA has been shown to act more potently than IAA in some instances. Further, it has been recently reported that the loss of IAA uptake carrier or efflux carrier does not affect the intracellular IBA transport. These results suggest that IBA transport and signaling pathways differ from IAA ones. However, the molecular mechanism of IBA specific transport or signaling pathways remains elusive. In the present study, we tried to elucidate the components of IBA specific pathway by screening novel IBA specific resistant mutants. From the screening, we recovered three mutant lines, which show only a specific resistance to IBA induced root growth inhibition and lateral root formation, but respond to other hormones and growth regulators exactly as does the wild type. All three mutants showed reduced transport activity for IBA but not IAA, indicating that the mutated genes may regulate the IBA specific transport process.
