University of Western Australia, WA 6009.
The 2004 discovery of the primary chemical component of burning vegetation that stimulates seed germination, has opened up a new area of fundamental plant biology. The original compound, karrikinolide, is one of a family of related compounds named karrikins. By employing Arabidopsis thaliana as a model genetic system to study karrikin mode of action, three different genes required for the karrikin response have been discovered. One such gene is also required for the action of strigolactone hormones, while the other two are close relatives of genes required strigolactone action. Studies of these genes suggest that early land plants probably employed an ancestral version of this genetic system as part of their developmental program. With the emergence of seed plants, elements of this genetic system apparently became replicated and specialised to mediate aspects of the control of root and shoot architecture by strigolactone hormones. Today, some parasitic plants exploit this modern strigolactone hormonal system to trigger germination of their seed, while fire-followers probably use elements of the more ancient genetic system to enable karrikins to trigger germination of their seed.