Hydrolyzes indole-3-acetamide (IAM) into indole-3-acetic acid (IAA). Plant hormone metabolism; auxin biosynthesis. Belongs to the amidase family. The plasmid pTiTM4 carries two T-regions, the TA and TB region, both of which have an IaaH gene, with low homology between them. Only the TB-IaaH gene seems to be functional.