The Role of Meristem-Identity Genes in Floral Patterning

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Weigel 9723818 Flowers give rise to fruits and seeds, which include all cereals, and thereby provide the majority of calories consumed by humans. Understanding the mechanisms of flower development is therefore interesting both from a scientific and from an economic point of view. This proposal focuses on the particular problem of how the pattern of organs within flowers is generated. The specific problem to be investigated is how a global regulator, LEAFY, which encodes a master switch for the initiation of individual flowers, controls the activity of a homeotic gene, APETALA3, whose expression is limited to the areas of the flower that will give rise to petals and stamens. While LEAFY is formally an upstream regulator of homeotic genes, it remains unclear how the transition is made from ubiquitous expression of LEAFY RNA and protein to region-specific expression of downstream genes. During the previous funding period, Dr. Weigel has developed several tools to address this problem. First, he has shown that activation of APETALA3is mediated by LEAFY in conjunction with a partially dispensable co-regulator, UFO. Second, he has shown that LEAFY is required for the proper expression pattern of UFO itself within flowers, which is normally activated after LEAFY, but before APETALA3. Third, he has shown that modifying the transcriptional activation potential of LEAFY in transgenic plants changes the expression patterns of downstream homeotic genes, suggesting that LEAFY encodes a transcription factor that acts directly on these target genes. He now proposes to investigate in detail how LEAFY and UFO cooperate to activate APETALA3, with the following specific aims: 1. Can an activated version of LEAFY bypass the requirement for UFO activity? 2. Does LEAFY protein, alone or together with UFO, interact directly with APETALA3 sequences? 3. How in turn is the expression pattern of UFO regulated and is LEAFY an activator of UFO in flowers, or does LEAFY merely refine the UFO expression pattern in flo wers? The conclusions drawn from these experiments will have not only implications for scientists interested in flower development, but should be applicable to the problems of pattern formation in any multicellular organism.