15th International Conference on Arabidopsis Research - TAIR

T06-025
A floral homeotic polymorphism in Capsella: studying
a hopeful monster
Guenter Theissen(1), Pia Nutt(1), Barbara Neuffer(2)
1-Department of Genetics, Friedrich Schiller University, Philosophenweg 12, D-07743 Jena,
Germany, e-mail: guenter.theissen@uni-jena.de
2-Department of Special Botany, University of Osnabrück, Barbarastr. 11, D-49076 Osnabrück;
e-mail: neuffer@biologie.uni-osnabrueck.de
The molecular basis of evolutionary novelties is a highly contentious issue.
While homeotic mutants and genes have been of tremendous value for
a better understanding of animal as well as plant development and form,
their role in evolution is highly controversial (1,2). It is often maintained that
homeotic mutants have such a drastic effect on the phenotype that fitness is
always heavily reduced, so that evolution generally proceeds in a gradualistic
and never in a saltational way. On the other hand there is both molecular and
morphological evidence that homeotic, or heterotopic, i.e. saltational changes
occurred during plant evolution and resulted in the establishment of new
lineages with novel morphological features (1,2). To better understand the
evolutionary significance of homeotic mutants we are studying a floral homeotic
variety of Capsella bursa-pastoris (shepherd’s purse) in which all petals
are transformed into stamens. In contrast to most other homeotic mutants
this “Staminoid petals” (Spe) variety occurs on several locations in larger populations
in the wild. It thus qualifies as a drastic morphological variant that
might have the potential to establish a new evolutionary lineage (a ‘hopeful
monster’ in Richard Goldschmidt’s provocative terminology). Due to its close
relationship to the model plant Arabidopsis, the Spe variant of Capsella can
be rigorously studied, from the molecular genetic basis of the phenotype to
its consequences on the ecology in the field. Respective investigations are
underway and may help to answer the long-standing question as to whether
non-gradualistic changes at the phenotypic level, such as homeotic transformations,
have the potential to contribute to macroevolution.
1. Theissen G (2000) Bioessays 22, 209-213
2. Ronse De Craene LP (2003) Int J Plant Sci 164 (5 Suppl.), S225-S230
15 th <strong>International</strong> <strong>Conference</strong> on Arabidopsis Research 2004 · Berlin
T06-026
The genomic pattern of polymorphism in Arabidopsis
thaliana
Chris Toomajian(1), Mattias Jakobsson(2), Badri Padhukasahasram(1), Vincent
Plagnol(1), Keyan Zhao(1), Joy Bergelson(3), Martin Kreitman(3), Magnus
Nordborg(1)
1-Molecular and Computational Biology, University of Southern California
2-Cell and Organism Biology, Lund University
3-Department of Ecology and Evolution, University of Chicago
Its wealth of naturally occurring variation, high level of inbreeding,
and resulting extensive linkage disequilibrium make Arabidopsis thaliana an
attractive model plant for carrying out genome-wide association mapping
studies. The genome-wide surveys necessary for association mapping will
also lead to a more comprehensive model of variation for a species and ultimately
a better understanding of the genetic process of adaptation to diverse
environments.
As part of a genome-wide survey of polymorphism in A. thaliana,
we have re-sequenced and processed data from 876 short (500-700 bp)
fragments distributed throughout the genome in a sample of 95 accessions
and identified thousands of SNPs.
Here we present the results of a population genetics analysis
of these data. We discuss how well the genome-wide pattern of variation
fits standard population genetics models, and what we have learned about
Arabidopsis population structure. We focus in particular on the influence that
the duplicated nature of the genome has on levels of polymorphism. We also
investigate the relationship between estimators of recombination rate and
levels of polymorphism across the genome. Finally, we show that despite the
limited value of tests that assume the standard population genetics model,
analyzing loci in light of the genome-wide empirical distribution of several
population genetics statistics can uncover possible traces of selection.
T06 Natural Variation and Comparative Genomics Including Genome