Interface between fungi and green algae in lichen associations

Abstract

It is widely recognized that the lichen is the product of a fungus and a photosynthetic partner (green alga or cyanobacterium), but its acceptance was slow to develop throughout history. The development of powerful microscopic and other lab techniques enabled better understanding of the interface between symbionts, beginning with the contentious concept of the dual nature of the lichen thallus. Even with accelerating progress in understanding the interface between symbionts, much more work is needed to reach a level of knowledge consistent with that of other fungal interactions. This minireview describes the interface between algal and fungal symbionts in lichens, including the appearance of interacting symbionts, our current understanding of communication between symbionts, and emerging new concepts in light of the challenges and debates that have provided lichenology with an enriched history. Communication between symbionts occurs before physical contact, which has been studied through microscopy, movement of molecules between symbionts, and gene expression studies. New discoveries include the interaction with more than one alga in a lichen thallus as well as other unrelated fungi and bacteria typically found on or within the thallus. This minireview briefly describes our current state of knowledge and highlights new directions for further study.