Claudia Voelckel

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I am taking a microarray approach towards understanding morphological and ecological differences across evolutionary young species of Pachycladon, an alpine cress, endemic to New Zealand and Tasmania.

I will focus on:

• comparisons of species representing two clades suggested to have diverged by specializing on different geological substrates - P. fastigiata and P. novae-zealandiae - as well as
• comparisons of species within a clade which differ in morphology (e.g. trichomes) and habitat parameters other than substrate (e.g. altitude preferences) - P. fastigiata & P. enysii.

Ideally, in each comparison, I would like to separate within species- from between species-variation to find fixed expression differences between species. Such differences are ultimately due to differences in cis or trans regulation and thus help to discover genetic differences between species. These genetic polymorphisms may then be searched for signatures of selection and further investigated regarding their role in adaptation and reproductive isolation. Microarray studies across species are therefore a first but very informative step in explaining the adaptive genetic changes that drive diversification. Moreover, gene expression differences can be correlated with phenotypic differences observed downstream of gene expression, e.g. differences in proteomes, metabolomes, morphology, behavior, physiology and ecology.

All microarray experiments will be conducted in close collaboration with Peter Heenan (Landcare Research, Lincoln) and Bart Jansen (HortResearch, Auckland), respectively.

The repeated loss of floral anthocyanins during the evolution of the North American Aquilegia clade, which is partly associated with shifts to hawkmoth pollination, represents an interesting case of parallel evolution. We are investigating if this convergence in phenotype is mediated by convergence on the molecular level, in particular, if the phenotypic changes are brought about by similar regulatory or structural mutations.

Ultimately, we are interested in answering the following questions:

• How strongly is the evolution of a trait constrained by pleiotropic effects? Is phenotypic evolution mostly due to regulatory mutations?
• How much adaptive genetic variation is maintained in a species and likely to be exchanged between species through hybridization?
• Do the genes apparently mediating an adaptive trait show signatures of selection?
• Can we show that a trait is adaptive by studying the fitness consequences of natural or artificial (bred or genetically engineered) polymorphisms of a candidate gene?

Anthocyanins are phenotypically and molecularly tractable, exhibit great variation across Aquilegia species and fulfill important ecological functions all of which predestines them for evolutionary studies.
Steps we take towards answering the above questions:

• Study the expression patterns of the six main structural genes underlying anthocyanin production across the North American columbine phylogeny (Whittall et al.)
• Clone the regulators of the anthocyanin biosynthetic pathway (ABP) and study their variation in expression and sequence across species
• Identify the molecular mechanism underlying the loss of floral anthocyanin in A. pubescens: Do any of the ABP loci map to a QTL for spur color?
• Establish causal links between genotype and phenotype by exchanging alleles via genetic engineering (transient transformation of Aquilegia by virus-induced gene silencing developed by Elena Kramer’s group)

Flowers ensure a plant’s reproduction by producing male and female gametes (in stamens and carpels, respectively) and by structures that promote the fusions of these gametes (conspicuous petals and sepals, nectary glands). Genes that determine which floral organ a floral meristem develops into have been extensively characterized in Arabidopsis thaliana as well as other eu-dicot plants and are widely known as ABC genes. By taking a microarray approach and studying gene expression patterns in the five floral whorls of Aquilegia formosa we are addressing several questions:

• How conserved is the ABC model at the base of the eu-dicots?
• What is the role of staminodia, a floral whorl inserted between stamens and carpels and that is specific to Aquilegia?
• Can petal-specific gene expression tell us something about the genes involved in the formation of the spur, a key innovation, believed to have accelerated speciation in the genus Aquilegia?

The arrays are designed based on an extensive EST collection (TIGR AQGI) in a concerted effort by Justin Borevitz (University of Chicago), Willem Rensik (The Institute of Genomic Research) and NimbleGen Systems, Inc.. They are customized high-density oligonucleotide arrays carrying about 17,800 genes with an average of 20 probes per unigene (a total of 356,000 spots).