Isolation and Positional Cloning of Methyl-Indole-3-Acetic Acid Resistant Mutants in Arabidopsis

Auxin is one of the most important plant hormones in that it regulates almost all aspects of plant growth and development. In plants, free indole-3-acetic acid (IAA) is the major active auxin and can be converted to methyl-IAA (MeIAA) with the activity of an IAA carboxyl methyltransferase 1 (IAMT1). However, MeIAA is also an inactive form of IAA and can be converted to IAA catalyzed by several esterases. MeIAA is a non-polar IAA form and can diffuse between cells, so MeIAA is suitable for screening new components in MeIAA metabolism or IAA biology. Here, we screened ethyl-methane-sulphonate (EMS)-mutagensis seedlings on MeIAA medium in the dark, with longer hypocotyls used as a criterion. We isolated 8 putative MeIAA-resistant mutants and carried out further experiments on one mutant, mir1. These new mutants will help shed light on MeIAA metabolism and the action mechanism of IAA.