Lichen photomorphs are discrete thalli developed by conspecific mycobionts with either a prokaryotic or eukaryotic photosynthetic partner. In other words, photomorphism is the ability for a single fungal species to associate with either a green alga or a cyanobacterium, hence forming thalli referred to as chloromorphs and cyanomorphs, respectively.
In the family Lobariaceae (henceforth subsumed under Peltigeraceae), in addition to exhibiting distinct physiological traits, photomorph pairs occasionally display dramatically different phenotypes (i.e., foliose chloromorphs vs. fruticose cyanomorphs). Because of their distinct morphology, these peculiar cyanomorphs were assigned to their own genus, Dendriscocaulon. However, DNA sequencing revealed that this taxon was conspecific with the fungal component within a photomorph pair. This “two lichens – one fungus” scenario constitutes an optimal model for addressing fundamental questions in the biology of symbiosis.
In the present study, we used morphologically dissimilar photomorphs in the genus Dendriscosticta (Lobarioideae, Peltigeraceae) as models in the study of evolutionary dynamics within symbiotic systems. Our main objective was to determine what factors allow for different symbiotic outcomes. In order to achieve this goal, metatranscriptome sequencing (RNA-seq) was carried out on 16 samples of Dendriscosticta (8 chloromorphs and 8 cyanomorphs). In complement, fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy were used to visualize photomorph-associated changes in the lichen microbiome. Ultimately this project aimed to: 1) identify the genes that are differentially expressed in photomorphs of Dendriscosticta, and characterize the genes that play a predominant role in the lichen symbiosis; 2) characterize the lichen microbiome in both photomorphs to further our understanding of its role in the symbiosis.
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