Catalyzes the synthesis of indole-3-acetic acid (IAA)-amino acid conjugates, providing a mechanism for the plant to cope with the presence of excess auxin (By similarity). Involved in red light-specific hypocotyl elongation. May act downstream of a red light signal transduction and determine the degree of hypocotyl elongation (PubMed:14581632). Expressed in cotyledons and hypocotyls. Belongs to the IAA-amido conjugating enzyme family.