InterPro domain: IPR044757

In higher plants, the growth regulator indole-3-acetic acid (IAA or auxin) is found both free and conjugated via amide bonding to a variety of amino acids and peptides, and via an ester linkage to carbohydrates. IAA-Asp conjugates are involved in homeostatic control, protection, storing and subsequent use of free IAA. IAA-Asp is also found in some plants as a unique intermediate for entering into IAA non-decarboxylative oxidative pathway. IAA amidohydrolases, which belong to the M20 family of peptidases, cleave the amide bond between the auxin and the conjugated amino acid to regulate IAA levels [ 1 ].

IAA-amino acid hydrolase ILR1 (IAA-LEUCINE RESISTANT 1) from Arabidopsis hydrolyses certain amino acid conjugates of IAA, including IAA-Phe, IAA-Leu and IAA-Tyr, although it can also use IAA-Ala, IAA-Gly, IAA-Met and IAA-Glu as substrates with lower efficiency, having no activity with IAA-Ile, IAA-1-O-beta-D-glucose or IAA-myo-inositol [ 2 , 3 , 4 ]. ILL4, also known as IAR3, hydrolyses IAA-Ala, IAA-Asn, IAA-Cys, IAA-Glu, IAA-Met, IAA-Ser and IAA-Gly [ 5 , 5 ] and has a lower efficiency with IAA-Phe, IAA-Leu and IAA-Val and no activity with IAA-Ile [ 5 , 5 ]. ILL4 also hydrolyses amino acid conjugates of jasmonic acid and 12-hydroxy jasmonic acid [ 5 ].

This entry includes ILR1 and ILR1-like proteins (ILL) from Arabidopsis thaliana and Oryza sativa.

1. Characterization of a family of IAA-amino acid conjugate hydrolases from Arabidopsis. J. Biol. Chem. 277, 20446-52
2. ILR1, an amidohydrolase that releases active indole-3-acetic acid from conjugates. Science 268, 1745-8
3. IAR3 encodes an auxin conjugate hydrolase from Arabidopsis. Plant Cell 11, 365-76
4. A family of auxin-conjugate hydrolases that contributes to free indole-3-acetic acid levels during Arabidopsis germination. Plant Physiol 135, 978-88
5. The amidohydrolases IAR3 and ILL6 contribute to jasmonoyl-isoleucine hormone turnover and generate 12-hydroxyjasmonic acid upon wounding in Arabidopsis leaves. J Biol Chem 288, 31701-14