The auxin family is by far the best studied family of plant hormones. Major breakthroughs have recently been reported concerning the molecular mechanisms of auxin signaling. Interestingly, auxin synthesis is not restricted to plants. Diverse bacterial and fungal species are known to produce auxin, with indole-3-acetic acid (IAA) as the best documented auxin molecule. Bacterial IAA synthesis is mostly studied in plant-associated bacteria, as IAA synthesis is linked to pathogenesis or plant growth promotion. IAA produced by bacteria has so far been regarded as an effector molecule. More recently it was found that IAA can act as a signal molecule in some bacteria and lower eukaryotes.
The structure of the natural auxin indole-3-acetic acid (IAA), produced by both plants and micro-organisms.