Title

Understanding the convergent evolution of C4 photosynthesis in plants. 

Abstract

Most plants use what is known as C3 photosynthesis because the first product of the pathway is a three carbon compound. In 1966, Hal Hatch and Roger Slack discovered a second photosynthetic pathway in plants that produces four carbon acids and so is called C4 photosynthesis. The changes to leaves required for the evolution of C4 photosynthesis from the ancestral C3 state are complex and include modifications to leaf development, cell biology and biochemistry. Despite this, the C4 pathway has evolved convergently in at least sixty-six distinct plant lineages. Based on experimentation and modelling I will propose that the repeated evolution of the complex C4 pathway is based on the flexible acquisition of traits and relatively minor remodelling to metabolic pathways that already operate in the ancestral C3 state. I will also provide evidence that the patterning of photosynthesis gene expression required in C4 leaves is based on pre-existing regulatory architectures that operate in C3 species. We conclude that the repeated evolution of the highly complex C4 trait has been facilitated by minor modifications to existing characters.