Reverse transcriptase-related enzymes are associated with horizontal chromosome transfer in an asexual pathogen

20 Supernumerary chromosomes have been shown to transfer horizontally from 21 one isolate to another. However, the mechanism by which horizontal chromosome 22 transfer (HCT) occurs is unknown. In this study, we compared the genomes of 11 23 isolates comprising six Fusarium species that cause soybean sudden death syndrome 24 (SDS) or bean root rot (BRR), and detected numerous instances of HCT in super25 numerary chromosomes. We also identified a statistically significant number (21 26 standard deviations above the mean) of single nucleotide polymorphisms (SNPs) in 27 the supernumerary chromosomes between isolates of the asexual pathogen F. vir28 guliforme. Supernumerary chromosomes carried reverse transcriptase-related genes 29 (RVT); the presence of long RVT open reading frames (ORFs) in the supernu30 merary chromosome was correlated with the presence of two or more chromosome 31 copies with a significant number of SNPs between them. Our results suggest that 32 supernumerary chromosomes transfer horizontally via an RNA intermediate. Un33 derstanding the mechanism by which HCT occurs will have a profound impact on 34 understanding evolution and applying biotechnology as well as accepting HCT as 35 a natural source of genetic variation. 36 2 PeerJ PrePrints | https://dx.doi.org/10.7287/peerj.preprints.1324v1 | CC-BY 4.0 Open Access | rec: 25 Aug 2015, publ: 25 Aug 2015 P re P rin ts