Evolution of Scent Genes

Plants produce a vast array of volatile organic compounds (VOCs), which play major roles in the interactions with their biotic and abiotic environments. In recent years, considerable research effort has aimed at the characterization of genes and enzymes involved in the biosynthesis of VOCs in plants. The elucidation of many VOC biosynthesis pathways in various plant species brought up the central question of the evolutionary origin of this remarkable chemical diversity. This chapter describes some of the molecular mechanisms, by which plants may acquire or loose the capacity to synthetize specific VOCs. On the one hand, many plant species have acquired the capacity to produce highly diversified blends of volatiles through different mechanisms leading to divergent evolution and pathway plasticity, such as the expansion of large gene families following gene duplication, catalytic promiscuity or easy change in substrate specificity within enzyme families. On the other hand, some compounds may be produced by unrelated enzymes, or even totally different pathways, which evolved independently in different plant species. As illustrations, examples have been selected from different categories of VOCs in various plant families, with an emphasis on scent and aroma compounds from plants of particular agronomical or horticultural interests.