Identification of a novel link connecting indole-3-acetamide with abscisic acid biosynthesis and signaling

Plants orchestrate their developmental processes and responses to environmental stimuli through a sophisticated network of small signaling molecules, termed phytohormones. Among these, auxins are recognized for their role in promoting plant growth. However, indole-3-acetamide (IAM), an auxin precursor, has been observed to inhibit primary root elongation. The molecular mechanism underlying this inhibitory effect remains largely unexplored. A comprehensive genome-wide association study (GWAS) conducted on a highly diverse collection of 166 wild Arabidopsis accessions from the Iberian Peninsula has identified several genomic regions associated with reduced IAM sensitivity under controlled in vitro conditions. This study highlighted ABA3 and GA2ox2 as possible candidate genes. Molecular and structural analyses suggest that the inhibition of primary root elongation induced by IAM is intricately associated with the enhanced production of abscisic acid (ABA) involving ABA3. Studies employing mutant and reporter lines have confirmed that IAM activates ABA signaling, thereby revealing a novel interaction between the auxin precursor IAM and ABA and suggesting an independent role for IAM as a signaling molecule in plant hormone crosstalk.