By Sean Henahan, Access Excellence

LA JOLLA, CA- Independent research teams have identified two genes that can transform ordinary shoots into flowers. And they have gone one step further, introducing the flower-stimulating genes into different plants, making them flower on demand.

The humble weed 'Arabidopsis thaliana' is the botanical equivalent of the drosophila fruit fly, the geneticist's favorite creature. Like the fruit fly, Arabidopsis has a relatively small genome that has been studied in depth. Arabidopsis would never flower were it not for a gene called LEAFY. When activated, the LEAFY gene transforms tissues that would normally form shoots to become flowers instead.

Researchers at the Salk Institute, in collaboration with another team in Sweden were able to demonstrate that leaving the LEAFY gene in the 'on' position makes the plant develop flowers much sooner than normal, and converts all lateral shoots into solitary flowers. The researchers then were able to introduce this gene into the completely unrelated aspen, creating a new transgenic hybrid. When the Arabidopsis LEAFY gene was forced to express itself, the aspen flowered much earlier than usual.

Another research team, made of scientists from the University of Arizona, Tucson, and University of California, San Diego, describe a similar result with a different gene, APETALA1. The team determined that this gene is also involved in transforming shoots into flowers and that keeping the APETALA1 gene in the 'on' position had much the same effect: converting shoots into flowers, and forcing much earlier flowering.

The researchers believe that the LEAFY gene is probably conserved in many unrelated plant species. This means it might be possible to manipulate the blooming of virtually any human food crop.

The leaves and flowers of Arabidopsis derive from the shoot meristem which is made of undifferentiated cells. In nature, a procession of genes responding to environmental cues regulates the development of leaves, inflorescences and flowers. Now, for the first time, scientists have been able to interrupt this order of events, by stimulating expression a single gene to confer floral identity on the undifferentiated cells. These findings will help researchers understand the diversity of growth and blooming seen in different species of plants.

The research is also likely to lead to applications in biotechnology. It might be possible to engineer crops to flower in different geographic locations with different growing seasons. Indeed, attempts to develop novel transgenic corn is now underway. The discovery could also speed up tree breeding programs now limited by the long life-cycle of trees. The research might also lead to non-agricultural applications, such as ornamental plants with unusual flowering patterns.

The complementary research results appeared in Nature, Vol.. 377, Oct. 12, '95: Weigel et al, pp. 495-499; Mandel et al., pp.482-483. Also see commentary, same issue.