Liverwort oil bodies: diversity, biochemistry, and molecular cell biology of the earliest secretory structure of land plants

Abstract

Liverworts are known for their large chemical diversity. Much of this diversity is synthesized and enclosed within the oil bodies (OB), a synapomorphy of the lineage. OB contain the biosynthetic enzymes to produce and store large quantities of sesquiterpenoids and other compounds while limiting their cytotoxicity. Recently, there were important biochemical and molecular discoveries related to OB formation, diversity and biochemistry that allows the comparison with other secretory structures of land plants in an evo-devo perspective. In this review, we address and discuss the most recent advances in OB origin, development and function to understand the importance of these organelles in liverwort physiology and adaptation to the changing environment. Our mapping of OB-types and chemical compounds to the current liverwort phylogeny suggests that OB were already present in the most recent common ancestor of liverworts, supporting OB evolved as the first secretory structure in land plants. Still, we require a better sampling to define the macroevolutionary pattern governing the ancestral type of OB. We conclude that current efforts in finding molecular mechanisms responsible for this morphological and chemical diversity of secretory structures will help understand the evolution of each major group of land plants, and open new avenues in biochemical research of bioactive compounds for both bryophytes and vascular plants.