Format: ORAL

Poquita-Du, R.C.1,2*, Otte, J.1, Calchera, A. 1,2, Nicolas Herrmann3, Claudia Bchel3 Schmitt, I.1,2,3

1 Senckenberg Biodiversity and Climate Research Center, Frankfurt am Main, Germany 2 LOEWE Center for Translational Biodiversity Genomics, Frankfurt am Main, Germany 3 Goethe University Frankfurt, Frankfurt am Main, Germany

The genus Trebouxia is a keystone lichen-forming green alga and is known to display a wide range of environmental tolerances. However, knowledge about the genome composition of different strains and what influences the varying levels of tolerance to stress within this genus remains scarce. Here, we report results from two connected studies including (1) a genome-wide comparative study concerning six Trebouxia strains, isolated from Umbilicaria phaea (Trebouxia clade A) and U. pustulata (Trebouxia clade S) and, (2) an experimental study to examine the photo-physiological performance of the six strains under high light conditions. We have assembled highly complete genomes of the six Trebouxia strains, with an average of 96% BUSCO completeness based on the Chlorophyta database. We found extensive genomic variation among, and even within Trebouxia clades with genome sizes and numbers of protein-coding genes ranging from 63.08-74.14 Mb and 14,109-18,870, respectively. Interestingly, we found differences in protein-coding genes associated with photosynthesis, suggesting differences in physiological capacities related to photosynthetic performance. To test this hypothesis, we performed an experiment to examine responses of the six Trebouxia strains to high light stress, after 1 hour and 3 days of exposure. We measured photo-physiological parameters (photosynthetic efficiency, non-photochemical quenching, chlorophyll a concentration) in combination with differential gene expression analysis via RNASeq. Preliminary results show among-strain differences in capacity to withstand high light stress, which likely stem from variation in their genomic composition, particularly regions associated to photosynthesis. Overall, our work demonstrates that unifying physiological and molecular mechanisms can provide important insights into the ecology and evolution of this important and most widespread lichen-forming green algal genus, Trebouxia.