The evolution of intracellular endosymbiosis marks a major transition in the biology of the host and endosymbiont. Yet, how adaptation manifests in the genomes of the participants remains relatively understudied. We investigated this question by sequencing the genomes of Tetrahymena utriculariae, a commensal of the aquatic carnivorous bladderwort Utricularia reflexa, and its intracellular algae, Micractinium tetrahymenae. We discovered an expansion in copy number and negative selection in a TLD domain-bearing gene family in the genome of T. utriculariae, identifying it as a candidate for being an adaptive response to oxidative stress resulting from the physiology of its endosymbionts. We found that the M. tetrahymenae genome is larger than those of other Micractinium and Chlorella and contains a greater number of rapidly expanding orthogroups. These were enriched for Gene Ontology terms relevant to the regulation of intracellular signal transduction and cellular responses to stress and stimulus. Single-exon tandem repeats were overrepresented in paralogs belonging to these rapidly expanding orthogroups, which implicates long terminal repeat retrotransposons (LTRs) as potential agents of adaptation. We additionally performed a comparative transcriptomic analysis of M. tetrahymenae in a free-living state and in endosymbiosis with T. utriculariae and discovered that the genes that are differentially expressed were enriched for pathways that evidence shifts in energy generation and storage and in cellular protection strategies. Together, our results elucidate the axes along which the participants must adapt in this young endosymbiosis and highlight evolutionary responses to stress as a shared trend.

• Klíčová slova
• LTR, ciliate, endosymbiosis, genome, green algae, stress, tandem gene duplications,
• MeSH
• biologická evoluce MeSH
• fyziologická adaptace * genetika   MeSH
• fyziologický stres genetika   MeSH
• molekulární evoluce MeSH
• symbióza * genetika   MeSH
• Tetrahymena * genetika   MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: Utricularia are rootless aquatic carnivorous plants which have recently attracted the attention of researchers due to the peculiarities of their miniaturized genomes. Here, we focus on a novel aspect of Utricularia ecophysiology-the interactions with and within the complex communities of microorganisms colonizing their traps and external surfaces. RESULTS: Bacteria, fungi, algae, and protozoa inhabit the miniature ecosystem of the Utricularia trap lumen and are involved in the regeneration of nutrients from complex organic matter. By combining molecular methods, microscopy, and other approaches to assess the trap-associated microbial community structure, diversity, function, as well as the nutrient turn-over potential of bacterivory, we gained insight into the nutrient acquisition strategies of the Utricularia hosts. CONCLUSIONS: We conclude that Utricularia traps can, in terms of their ecophysiological function, be compared to microbial cultivators or farms, which center around complex microbial consortia acting synergistically to convert complex organic matter, often of algal origin, into a source of utilizable nutrients for the plants.

• Klíčová slova
• Algae, Bacteria, Ciliate bacterivory, Digestive mutualism, Fungi, Herbivory, Nutrient turnover, Plant–microbe interactions, Protists, Utricularia traps,
• MeSH
• Bacteria klasifikace   genetika   izolace a purifikace   MeSH
• DNA bakterií genetika   MeSH
• DNA fungální genetika   MeSH
• DNA řas genetika   MeSH
• fylogeneze MeSH
• hluchavkotvaré mikrobiologie   fyziologie   MeSH
• houby klasifikace   genetika   izolace a purifikace   MeSH
• metagenomika metody   MeSH
• mikrobiální společenstva MeSH
• stanovení celkové genové exprese metody   MeSH
• vodní organismy mikrobiologie   fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA bakterií MeSH
• DNA fungální MeSH
• DNA řas MeSH