Search

The article discusses the current proposals to redefine lichens and highlights the disadvantages of these proposals. Lichens are currently defined as a symbiotic relationship between a fungus (mycobiont) and an alga or cyanobacterium (photobiont). However, some lichen biologists have suggested expanding this definition to include other microorganisms that colonize the lichen thallus. The article argues that these proposals are not justified because the roles and significance of these additional microorganisms are still poorly understood and their inclusion would blur the distinction between lichens and other ecosystems. The article concludes that the current definition of lichens as a partnership between mycobiont and photobiont remains meaningful and should not be amended. [Extracted from the article]

This article is a Commentary on Spribille et al. (2022), 234: 1566–1582. [ABSTRACT FROM AUTHOR]

This article is a Commentary on Mark et al. (2020), 227: 1362–1375. [ABSTRACT FROM AUTHOR]

Dictyochloropsis s.l. is an ecologically important, common but little-studied genus of green algae. Here, we examined the diversity and host selectivity of algae attributed to this genus at both species-to-species and species-to-community levels., We conducted a molecular investigation of 15 cultured strains and several lichen photobionts, using 18S rRNA, rbcL and ITS sequence data. We further used seven alga-specific microsatellite markers to study algal sharing among fungi of the family Lobariaceae in two populations in Madeira and Taiwan (454 lichens)., We found that the genus Dictyochloropsis s.l. is polyphyletic. Dictyochloropsis clade 1 comprises only free-living algae whereas Dictyochloropsis clade 2 includes lichenized algae as well as free-living algae. Fungal selectivity towards algae belonging to Dictyochloropsis clade 2 is high. Selectivity varies geographically, with photobionts being restricted to a single region. Finally, we showed that Dictyochloropsis clade 2 individuals are shared among different fungal hosts in communities of lichens of the Lobariaceae., As for other green algal lineages, there is a high amount of cryptic diversity in Dictyochloropsis. Furthermore, co-evolution between Dictyochloropsis clade 2 algae and representatives of the Lobariaceae is manifested at the community level, with several unrelated fungal species being horizontally connected by shared photobiont clones. [ABSTRACT FROM AUTHOR]

Summary • The lichen Lobaria pulmonaria survives large seasonal environmental changes through physiological acclimation to ambient conditions. • We quantitated algal cell population, cell division and key macromolecular levels associated with photosynthesis and nitrogen metabolism in L. pulmonaria sampled from four seasons with contrasting environmental conditions in a deciduous forest. • The algal symbiont population did not vary seasonally and cell division was restricted to the newest thallus margins. Nevertheless the symbiont concentrations of chlorophyll, PsbS, PsbA, and RbcL changed significantly through the seasons in the nondividing algal cells from older thallus regions. • L. pulmonaria reversibly allocated resources toward photochemical electron generation and carbohydrate production through the spring, summer and fall, and towards photoprotective dissipation in the cold, high-light winter. Our study shows that large seasonal molecular acclimation in L. pulmonaria occurs within a nearly stable, nondividing algal cell population that maintains photosynthetic capacity through many years of changing environmental cues. [ABSTRACT FROM AUTHOR]

Summary • To examine the mode of dispersal and photobiont selectivity of Fulgensia fulgida we investigated the photobionts associated with the lichens of a community related to the Toninio–Psoretum decipientis association. • Photobionts and mycobionts were analysed using morphological (light microscopy) and molecular (internal transcribed spacer (ITS) and partial large subunit (LSU) nuclear ribosomal DNA sequencing) techniques. • The thalli of the mycobiont of F. fulgida , which were identical in their ITS and partial LSU-sequence, contained two strains of Trebouxia asymmetrica , one of them also present in a thallus of Toninia sedifolia . Other co-occurring lichens, namely Squamarina lentigera , Catapyrenium michelii and Collema cristatum , were shown to have Asterochloris irregularis , Myrmecia and Nostoc as photobionts. • It is suggested that F. fulgida is selective in its photobiont choice, that dispersal of the lichen has occurred by way of ascospores and subsequent independent relichenization events and that F. fulgida and T. sedifolia share the same photobiont pool. The results also suggest possible mechanisms of relichenization and strategies for future research on the selectivity of lichen bionts. [ABSTRACT FROM AUTHOR]

The activity of the enzyme carbonic anhydrase (CA; E.C. 4.2. 1 . 1) was examined in eight specks of lichen in vivo measurements of 18O exchange from doubly labelled CO2 ( 12C18O18O) to water, with the aim of determining whether this enzyme is present in lichens and if so to what extent it participates in physiological processes. The lichens were chosen to represent different mycobiont (Heterodera, Leptogium, Lobaria, Peltigera, Pseudocyphellaria, Xantoparmelia) and photobiont (Coccomyxa, Dictyochloropsis, Mymecia, Nostoc, Trebouxia) genera as well as varying morphology. All lichens were found to possess considerable activity of CA, which varied by a factor of about four between the species when compared on a chlorophyl basis, arid by a factor of about 10 when related to the weight. Incubation of lichen thalli with ethoxyzolamide (EZA) and acetazolamide (AZA). which inhibit intracellular and extracellular CA respectively, showed that intracellular CA was present in all of the species. Incubation with EZA also resulted in inhibition to photosynthetic CO2 uptake in all species suggesting a role of internal CA in the CO2 acquisition process in all the investigated photobiont genera. A pan of the CA activity was inhibited by AZA in all except two of two four cyanobacterial Nostoc lichens, indicating the possible presence of extracellular forms of CA. This CA also appeared to he involved in the acquisition of CO2 as AZA inhibited photosynthesis CO2 uptake in these lichens. The CA inhibitors also affected CO2 efflux in the dark, i.e. fungal respiration, which was inhibited by both AZA and EZA in six of the species, suggesting that a proportion of the CA activity might be located in the mycobiont. [ABSTRACT FROM AUTHOR]