Differential responses to salt concentrations of lichen photobiont strains isolated from lichens occurring in different littoral zones

Abstract

An interesting biota of lichen-forming fungi occurs along rocky seashores of cold and warm-temperate regions in both hemispheres. Most of the species belong to the family Verrucariaceae and form symbioses with an extraordinarily diverse group of photobionts. We isolated the photobionts of three species: Hydropunctaria maura and H. amphibia from the supralittoral zone, and Wahlenbergiella striatula from the upper intertidal zone. We characterized the isolated strains structurally by means of transmission electron microscopy, and molecularly using the nrSSU and nrITS and chloroplast RPL10A regions. Additionally, we studied the response of the strains to different salt concentrations, analyzed the concentration of osmoregulatory solutes, and measured photosynthesis performance by chlorophyll fluorescence and CO2 assimilation techniques. All strains belong to the recently described species Halofilum ramosum, although we found differences in the ITS and RPL10A regions among the strains shared by H. maura and H. amphibia and the strain isolated from W. striatula. Differences were also found in the main osmoregulatory response of the strains growing under high salt concentrations: W. striatula accumulated glycerol, while H. maura and H. amphibia synthetized sucrose. Analyses of photosynthesis performance also indicated differences in physiological behavior between supralittoral-dwelling and intertidal-dwelling species, W. striatula showing lower photosynthetic activity under high irradiance. Our results highlight the role of photobionts in determining lichen zonation on rocky seashores.

Complex photobiont diversity in the marine lichen Lichina pygmaea

“…The exact nature of the relationship of L. pygmaea and Blidingia is yet to be established, but hints toward a unique interaction that has been previously overlooked. The other potential photobiont, Paulbroadya is known to form symbioses with several other freshwater and marine lichens in the family Verrucariaceae (Thüs et al ., 2011; Gasulla et al ., 2019) (Figure 5). The relationship here between the L. pygmaea -associated Paulbroadya and the same genus associated with the crustose marine lichen H. maura indicates the potential for sharing of photobionts between marine lichens.…”

Amphitropical variation of the algal partners of Pseudephebe (Parmeliaceae, lichenized fungi)

“…Two unlinked, nuclear algal markers were amplified: the Internal Transcribed Spacer of the ribosomal DNA (ITS), and the protein-coding RPL10A gene. The latter includes an hypervariable region that is useful for the molecular characterization of Trebouxiophyceae algae involved in lichen symbioses and, more specifically, for unravelling their phylogeographic structure (del Campo et al 2013;Gasulla et al 2019). The ITS was amplified using primers nr-SSU-1780-5′ and ITS4T (Kroken and Taylor 2000;Piercey-Normore and DePriest 2001) and PCR-PuRe-Taq Ready-to-Go Beads (GE Healthcare) following the manufacturers' instructions.…”

Coastal Lichens

“…Confirmation of the important role of the photobiont in adapting to salinization conditions of lichens was also registered in physiological experiments (Gasulla et al 2019). In laboratory conditions, the results of osmoregulatory responses of algae strains isolated from three lichen species were obtained: Hydropunctaria maura and H. amphibia from the supralittoral and Wahlenbergiella striatula from the littoral.…”

“…The differences were in response strategies for high salt concentrations: W. striatula accumulated glycerol, while H. maura and H. amphibia synthesized sucrose. Analysis of the effectiveness of photosynthesis also revealed differences: strains of algae from the thalli of W. striatula, living on the littoral, showed lower photosynthetic activity under high irradiation (Gasulla et al 2019).…”