Mechanisms of metabolic diversification in plants

Groups of non‐homologous functionally‐related genes are commonplace in bacteria, where they are mostly organised as operons. Gene clusters are rare in eukaryotes and usually consist of paralogs that have evolved through gene duplication. However clusters of functionally‐related but non‐homologous genes have been discovered in eukaryotic microbes and animals, and are now emerging as a new theme in plant biology. So far nine such clusters have been found in plants, all encoding genes for the synthesis of secondary metabolites associated with biotic/abiotic stress tolerance. These secondary metabolic gene clusters are amongst the most diverse and rapidly evolving features of plant genomes and provide tantalizing links with adaptive genome plasticity in microbes and animals. The fact that such clusters are often restricted to narrow taxonomic bands marks them as among the most diverse and rapidly evolving features of plant genomes, as such providing excellent read‐outs for investigating genome plasticity and mechanisms of adaptive evolution. The study of these clusters will yield new insights into the rules and mechanisms governing the formation, function, maintenance and dissipation of operon‐like metabolic gene clusters in plants, and into plant genome dynamics and the factors that shape genome architecture.