Abstract  - Prior to the discovery of C4 photosynthesis by Hal Hatch and Roger Slack in 1966 there were clues that some plants partitioned photosynthesis between specific leaf cell types. Elucidation of the full C4 pathway rationalised this compartmentation, and since then it has become clear that the careful partitioning of photosynthesis between two cell types is found in almost all of the sixty-six lineages of plants known to have evolved the C4 pathway. However, the molecular mechanisms responsible for this patterning of gene expression have remained elusive. We recently reported a bipartite interaction between MYB and MYC transcription factors that is necessary and sufficient for expression in bundle sheath cells of the C3 model Arabidopsis thaliana. We now think this network also operates in C4 leaves, and I will provide evidence for this. Moreover, using Arabidopsis we have discovered additional regulatory elements that drive expression in bundle sheath cells, and I will discuss how these may be important for the evolution of C4 gene expression. Taken together, our data define transcription factors that can pattern gene expression to the cell types associated with C4 photosynthesis. The findings are consistent with the notion that during evolution of the pathway, C4 genes acquire pre-existing cis-elements such that they become subject to gene regulatory networks controlling cell specificity in the ancestral C3 state.

Biography  - Julian is Professor of Photosynthesis at the University of Cambridge. His work has focused on identifying the ancestral role of C₄ proteins in C₃ plants and alterations to the regulation of genes encoding these proteins. Currently, his laboratory works on both dicot and monocot lineages that contain C₃ and C₄ species, and combines the use of synthetic biology, high throughput sequencing analysis and bioinformatics. Experiments are informed by phylogenetic reconstructions, and the long term aim is to better understand evolution of the complex C₄ phenotype.