Early germline sequestration in a basidiomycete fungus.

In sexual organisms, inheritance of new mutations is highly dependent on the timing of germline definition. Here, we used the fairy ring–forming fungus Marasmius oreades to challenge the general assumption of a late germline separation in the Fungi. We collected mushrooms from different parts of rings over a 7-year period and identified new mutations in different tissues by whole-genome sequencing. We found evidence that fertile and sterile tissues had accumulated different mutations, suggesting that the germ line, destined for spore production, is already defined in the mycelium in this species. Moreover, the germ line carried fewer mutations than sterile tissues, indicating a lower mutation rate. Our findings suggest that early germline sequestration is more widespread than previously considered across multicellular life. Editor's summary: Plants and fungi have long been thought to generate their germlines late in development, creating opportunities for somatic mutations to accrue and affect reproductive cells. Hiltunen Thorén et al. sequenced sterile and reproductive tissues from the fairy ring mushroom (Marasmius oreades) over 7 years and found that spores and lamellae, which are reproductive tissues, demonstrated consistently different mutations than sterile parts of the fruiting body. This suggests that these reproductive tissues may be sequestered early on in development. This observation in fungi expands the set of taxa that have independently evolved germline sequestration. —Corinne Simonti [ABSTRACT FROM AUTHOR]