Abstract 237 11.1 Introduction 238 11.2 How Many Nuclear Genes of Plants Are of Cyanobacterial Origin? 238 11.3 Reconstruction of More Recent Instances of Plastid-to-Nucleus

Gene Transfers 240 11.4 Functions of Cyanobacterium-Derived Proteins in the Plant Cell 240

11.4.1 Chloroplasts: Cyanobacterial Inheritance vs. Eukaryotic Invention 241 11.4.2 Photosystem I and Plastid Ribosomes 241 11.4.3 The Calvin Cycle and Glycolysis 242 11.4.4 Massive Rerouting of Cyanobacterial Proteins 243

11.5 Why Have Plastids Retained a Genome? 243 11.6 Consequences of Plastid-to-Nucleus Gene Transfer for Transport,

Signaling and Development 246 11.6.1 Transport 246 11.6.2 Plastid-to-Nucleus Signaling 246 11.6.3 Development 247

11.7 Conclusions 248 Acknowledgments 250 References 250

The acquisition of a cyanobacterial endosymbiont by an ancestral host cell resulted in the establishment of chloroplasts. The evolution of the new organelle occurred mainly via gene loss, together with a massive transfer of genes to the nucleus. Genome-wide comparative analyses have substantially improved our understanding of the extent and consequences of this large-scale gene transfer. Genes from the plastid ancestor have been a rich source of genetic material for the evolution of new cellular functions, as is documented in this chapter.