抖阴旅行射 Boulder researchers have discovered the first known molecular evidence of obligate symbiosis in lichens, a distinctive co-evolutionary relationship that could shed new light on how and why some multicellular organisms consolidate their genomes in order to co-exist.
The new study, which was today in the journal Molecular Ecology, finds that fungal organisms reduce their core genomic makeup while coalescing with algae to form a lichen partnership, one presumed to be "obligate" (i.e., requiring both partners) but had previously lacked direct genetic verification.
鈥淪ymbioses allows two different organisms to survive in areas where they otherwise might not be able to grow,鈥� said Erin Tripp, Curator of Botany at 抖阴旅行射鈥檚 Museum of Natural History and a co-author of the new study. 鈥淭hese findings are exciting because they illustrate a key genetic underpinning of this obligate pairing.鈥�
Lichens are omnipresent worldwide and may cover up to six percent of the Earth鈥檚 land mass. There are over 20,000 known lichen species, some of which are well-suited to extreme environments like deserts and arctic tundra. Lichens play an important role in ecological processes such as soil formation听and serve as bioindicators of environmental toxicity.
The genetic mechanisms and consequences of these fungal-algal unions, however, have remained poorly understood. Using samples collected from the southern Appalachian Mountains, the 抖阴旅行射 Boulder researchers sequenced DNA from 22 separate lichen species in order to better understand how the two unrelated organisms co-evolve on a molecular level.
The findings revealed that in some cases, the fungal partner of this symbiosis streamlined its mitochondrial genome, much like a couple moving in together might get rid of duplicate household furnishings.
鈥淭he fungus lost a crucial energy-producing gene while the algae retained a full-length copy of this gene,鈥� said Cloe Pogoda, lead author of the study and a graduate researcher in 抖阴旅行射 Boulder鈥檚 . 鈥淲e observed a parallel loss of this gene in three different lichen lineages.听The fungus gives up this particular gene while its photosynthetic partner keeps it."
This obligate arrangement鈥攊n which one partner relinquishes its own mitochondrial power supply to likely become reliant on its partner for cellular energy鈥攕uggests a genetic division of labor that makes the resulting lichen more efficient, Tripp said, thereby perhaps conferring an ecological advantage.
The researchers plan to expand the study to include more lichen species in the future. The findings could also inspire new inquiries into the human gut microbiome, the complex bacterial colony that lives symbiotically inside each person and has been shown to influence various aspects of health.
鈥淭he implications are far-reaching, given how many symbiotic relationships we observe in nature,鈥� said Tripp, who is also an assistant professor in 抖阴旅行射 Boulder鈥檚 Department of Ecology and Evolutionary Biology (EBIO). 鈥淣ow we can expand our scope of study to look for genomic signatures of co-evolution in other organisms.鈥�
抖阴旅行射 Boulder undergraduates helped assemble the genomic information using sequencing resources at 抖阴旅行射鈥檚 BioFrontiers Institute. Co-authors of the new research include Kyle Keepers and Nolan Kane of EBIO and James Lendemer of the New York Botanical Garden.
The National Science Foundation鈥檚 research program provided funding for the study.
