Advances in Understanding of Desiccation Tolerance of Lichens and Lichen-Forming Algae

Abstract

Lichens are symbiotic associations (holobionts) established between fungi (mycobionts) and certain groups of cyanobacteria or unicellular green algae (photobionts). This symbiotic association has been essential in the colonization of terrestrial dry habitats. Lichens possess key mechanisms involved in desiccation tolerance (DT) that are constitutively present such as high amounts of polyols, LEA proteins, HSPs, a powerful antioxidant system, thylakoidal oligogalactolipids, etc. This strategy allows them to be always ready to survive drastic changes in their water content. However, several studies indicate that at least some protective mechanisms require a minimal time to be induced, such as the induction of the antioxidant system, the activation of non-photochemical quenching including the de-epoxidation of violaxanthin to zeaxanthin, lipid membrane remodeling, changes in the proportions of polyols, ultrastructural changes, marked polysaccharide remodeling of the cell wall, etc. Although DT in lichens is achieved mainly through constitutive mechanisms, the induction of protection mechanisms might allow them to face desiccation stress in a better condition. The proportion and relevance of constitutive and inducible DT mechanisms seem to be related to the ecology at which lichens are adapted to.

Systems biology of resurrection plants

“…Of the non-angiosperm species, proteomics datasets are available for the moss P. patens [ 177 , 178 ], the Selaginella spikemosses S. bryopteris [ 179 ] and S. tamscarina [ 180 ] and the green alga Asterochloris erici [ 181 ]. The existing studies largely confirm the observations and predictions made from transcriptomic data [ 121 , 182 – 184 ]. Unsurprisingly, many proteins show specific patterns of expression in drying tissue or display altered abundance throughout the dehydration-rehydration cycle.…”

Evolutionary biology of lichen symbioses

“…The adaptations that have enabled the lichen lifestyle are still just beginning to be understood, but a unifying theme is the capacity of lichens for anhydrobiosis, the ability of cells to survive periods of very low water content (Gasulla et al ., 2021). Algal symbionts achieve this through vitrification, the conversion to a glassy state (Fernández‐Marín et al ., 2019; Candotto Carniel et al ., 2021).…”

Modeling in yeast how rDNA introns slow growth and increase desiccation tolerance in lichens

“…As the introduction of just two nonself-splicing rDNA introns is quite disruptive to yeast, we imagine that the evolutionary insertion of many introns into mycobiont rDNA was gradual, providing time for selection to turn partial disruptions of RiBi and DNA replication into adaptations. The importance of constitutive stress-defenses in lichens has been also recognized by Gasulla et al (2021) .…”

“…This work focuses exclusively on mycobionts. For a review of lichen desiccation tolerance which includes photobionts see Gasulla et al (2021 ).…”