Identification of rfk-1, a meiotic driver undergoing RNA editing in neurospora

Authors: HARVEY, A - Illinois State University; RHOADES, N - Illinois State University; SAMARAJEEWA, D - Illinois State University; SVEDBERG, J - Uppsala University; MANITCHOTPISIT, P - Illinois State University; SHARP, K - Illinois State University; REHARD, D - University Of Missouri; Brown, Daren; JOHANNESSON, H - Uppsala University; SHIU, P. K - University Of Missouri; HAMMOND, T - Illinois State University

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2019
Publication Date: 3/27/2019
Citation: Rhoades, N.A., Harvey, A.M., Samarajeewa, D.A., Svedberg, J., Yusifov, A.,Abusharekh, A., Manitchotpisit, P., Brown, D.W., Sharp, K.J., Rehard, D.G., et al. 2019. Identification of rfk-1, a meiotic driver undergoing RNA editing in neurospora. Genetics. 212(1):93-110. https://doi.org/10.1534/genetics.119.302122.
DOI: https://doi.org/10.1534/genetics.119.302122

Interpretive Summary: The process by which genetic elements in some fungi are passed on to successive generations in a very biased manner is known as meiotic drive. In Neurospora crassa and Fusarium verticillioides, when a parent with a meiotic drive called Spore Killer is crossed with a sensitive parent of the same fungus, half of the progeny die. Almost all of the surviving progeny have the Spore Killer element. How this meiotic drive process occurs is unknown. In this study, we identified a genetic element that is required for spore killing in N. crassa. Deletion of this element results in strains that are unable to cause spore killing while addition of the element into a previously sensitive strain led to the death of half of the progeny from a cross with a sensitive strain. We also found that the element in a N. crassa mutant strain unable to kill spores had six nucleotide differences of which one or more could cause it to be non-functional and not kill half of the sexual spores or progeny from a mating. This research provides knowledge of a mechanism that could be harnessed to target populations of fungi to limit an undesirable trait. For example, F. verticillioides produce the carcinogen fumonisin that may accumulate in crops and threaten animal and human health. Understanding how meiotic drive works in fungi will be of use to plant pathologists, plant breeders, and other scientists involved in the development of new ways to limit diseases and toxin contamination in corn.

Technical Abstract: Meiotic drive is a phenomenon where genetic elements demonstrate a capacity to be transmitted through meiosis to the next generation in a biased manner. A classic example of meiotic drive is found in Spore killer-2 (Sk-2), a meiotic drive element in Neurospora fungi. When Sk-2 is crossed with a Spore killer sensitive mating partner (SkS) nearly all of the surviving progeny of the cross are of the Sk-2 genotype. Analysis of the ascospore sacs, which hold the progeny after sexual reproduction, finds that half of the progeny are dead. The dead progeny are presumed to be of the SkS genotype. The mechanistic details of Sk-2-based meiotic drive are unknown. A recent model called the Killer Neutralization Model has proposed the existence of a resistance protein and a killer molecule. While a resistance protein has been identified, the identity of the killer remains unknown. Previous work has identified a locus called rfk-1, which is required for spore killing and has been mapped to a 45 kilobase (kb) region of chromosome III (within Sk-2). Here, we identify a genetic element that is both required and sufficient for spore killing. This element is contained within a 1481 base pair interval (called AH36Sk-2) of DNA from the 45 kb rfk-1 region. Deletion of this interval from Sk-2 results in loss of spore killing while placement of the interval in SkS creates a meiotic abortion phenotype consistent with the presence of a killer. Additionally, the same interval in an rfk-1 mutant (called AH363211) does not cause meiotic abortion upon transfer to SkS. Sequencing analysis has identified six mutations, one or more of which could be responsible for loss of the abortion phenotype. Although details on the identity of the killer still remain somewhat obscure, we present evidence the AH36 interval contains a region with homology to a predicted protein from Neurospora tetrasperma. Future work will seek to determine the nature of the killer within AH36, as well as its relationship to the previously defined rfk-1 locus.