Beschreibung:
<jats:title>Summary</jats:title><jats:p>
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<jats:list-item><jats:p>Lichens are exemplar symbioses based upon carbon exchange between photobionts and their mycobiont hosts. Historically considered a two‐way relationship, some lichen symbioses have been shown to contain multiple photobiont partners; however, the way in which these photobiont communities react to environmental change is poorly understood.</jats:p></jats:list-item>
<jats:list-item><jats:p><jats:italic>Lichina pygmaea</jats:italic> is a marine cyanolichen that inhabits rocky seashores where it is submerged in seawater during every tidal cycle. Recent work has indicated that <jats:italic>L. pygmaea</jats:italic> has a complex photobiont community including the cyanobionts <jats:italic>Rivularia</jats:italic> and <jats:italic>Pleurocapsa</jats:italic>. We performed rRNA‐based metabarcoding and mRNA metatranscriptomics of the <jats:italic>L. pygmaea</jats:italic> holobiont at high and low tide to investigate community response to immersion in seawater.</jats:p></jats:list-item>
<jats:list-item><jats:p>Carbon exchange in <jats:italic>L. pygmaea</jats:italic> is a dynamic process, influenced by both tidal cycle and the biology of the individual symbiotic components. The mycobiont and two cyanobiont partners exhibit distinct transcriptional responses to seawater hydration.</jats:p></jats:list-item>
<jats:list-item><jats:p>Sugar‐based compatible solutes produced by <jats:italic>Rivularia</jats:italic> and <jats:italic>Pleurocapsa</jats:italic> in response to seawater are a potential source of carbon to the mycobiont. We propose that extracellular processing of photobiont‐derived polysaccharides is a fundamental step in carbon acquisition by <jats:italic>L. pygmaea</jats:italic> and is analogous to uptake of plant‐derived carbon in ectomycorrhizal symbioses.</jats:p></jats:list-item>
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