Evolution of Development and Physiology
Kilinc, Aydin , Smyth, David R .
Evolution of an enhancer region that regulates PETAL LOSS expression in the perianth of the Arabidopsis flower.
An outstanding issue in biology is the evolution of complex forms, and how changes in regulatory networks drive this process. Flower structure in the Brassicaceae is remarkably conserved. The outermost whorl consists of four sepals, and the second whorl contains four petals arising between them, giving a distinctive cross-shaped appearance.
The PETAL LOSS (PTL) gene encodes a transcription factor of the trihelix family with 28 members in Arabidopsis. The ptl mutant phenotype is characterized by aberrant sepal development and a partial loss of petals. PTL is expressed between developing sepal primordia (termed the inter sepal zone, ISZ) where it suppresses growth. This keeps the sepals separate, and also limits the size of nearby sites for petal initiation.
We have identified a highly conserved enhancer region within the single long intron of PTL, and have shown that it activates expression in the ISZ. However, this sequence is apparently absent in the intron of PTL orthologs from outside the order Brassicales. Here we show that, within the Brassicales, a switch from 5-fold to 4-fold symmetry of the perianth coincides with the presence of a long intron containing the enhancer region. Furthermore, this region shows close homology to a sequence within the LTRs of a gypsy-like retrotransposon family, and that simple mutation in the LTR sequence is capable of activating expression in the ISZ. PTL function may have been recruited to the ISZ regions of the flower via the insertion of a retroelement into the intron of an ancestral PTL gene, and that this was associated with a change from pentamery to tetramery.
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1 - Monash University, School of Biological Sciences
2 - Monash University, School of Biological Sciences, Clayton Campus, Melbourne, Vic, 3800, Australia
Presentation Type: ASPB Minisymposium
Location: Continental B/Hilton
Date: Monday, July 9th, 2007
Time: 11:05 AM