IAM triggers ABA biosynthesis and signalling

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We are very happy that our most recent work got eventually published in New Phytologist. Our study investigates the molecular mechanism behind the observation that IAM, a precursor to the growth hormone auxin, inhibits primary root elongation. Through a genome-wide association study (GWAS) on wild Arabidopsis thaliana accessions from the Iberian Peninsula, we identified a number of candidate genes, and specifically focused on ABA3, a key enzyme in ABA biosynthesis. Experimental results using mutant lines and reporter assays confirm that IAM activates ABA signalling in the roots, suggesting that IAM acts as an independent signalling molecule in plant hormone crosstalk to regulate root growth and potentially manage abiotic stress responses.

Moya-Cuevas, J. et al. 2025 New Phytologist

Synopsis:
Plants orchestrate their developmental processes and responses to environmental stimuli through a sophisticated network of small signalling molecules, termed phytohormones. Among these, auxins are recognised 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 signalling, thereby revealing a novel interaction between the auxin precursor IAM and ABA and suggesting an independent role for IAM as a signalling molecule in plant hormone crosstalk.