Adaptomics: The Evolution of C4 Photosynthesis in the Brassicales

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C4 photosynthesis has evolved at least 60-times independently from C3 ancestors in both mono- and dicotyledonous seed plant families. It thus represents a remarkable example of convergent evolution of a complex adaptive trait. C4 photosynthesis can be considered as an adaptation to high temperatures and low water availability, or, more generally, to conditions of abiotic stress. Simply spoken, the emerging model of how C4 plants evolve from C3 ancestors posits that genes that are already present in C3 plants undergo changes in their expression strength and their expression domains in the course of C4 evolution, which is frequently accompanied (or predated) by gene and/or genome duplications. Beyond this general model, the genetic and molecular mechanisms underlying this complex adaptive trait are not well understood. The discovery of several C4 photosynthetic species in the family Cleomaceae, a sister family to the Brassicaceae within the Brassicales, and of C3-C4 photosynthetic intermediate species in the genus Moricandia within the Brassicales now makes it possible to capitalize on the resources and tools available for the model plant species Arabidopsis thaliana for dissecting the genetic and molecular mechanisms underlying the C4 trait in the Brassicales. Specifically, this proposal aims at the identification and functional analysis of genes governing the C4 trait through genome-wide comparative analyses of C3, C3-C4 intermediates, and C4 Brassicaceae and Cleomaceae. Hypotheses derived from comparative analysis will be tested by repression and mis-expression of candidate genes in transgenic Arabidopsis and Moricandia spec.