Authors
V Yurchenko1; AY Kostygov1; D Grybchuk2; A Zakharova1; A Saura1; ES Gerasimov3; 1 University of Ostrava, Czech Republic; 2 Central European Institute of Technology, Masaryk University,, Czech Republic; 3 Moscow State University, Moscow, Russian Federation Discussion
Leishmania spp. are important pathogens causing a vector-borne disease with a broad range of clinical manifestations from self-healing ulcers to the life-threatening visceral forms. Presence of Leishmania RNA virus (LRV) confers survival advantage to these parasites by suppressing antileishmanial immunity in the vertebrate host. The two viral species, LRV1 and LRV2 infect species of the subgenera Viannia and Leishmania, respectively. Here, we investigated co-phylogenetic patterns of leishmaniae and their viruses on a small scale (LRV2 in L. major) and demonstrated their predominant coevolution, occasionally broken by intraspecific host switches. This contrasts with a co-phylogenetic pattern of LRV1 and Leishmania (Viannia). To better understand how LRVs are intermingled with host metabolism, we established LRV1- and LRV2-negative strains of L. guyanensis M4147 and L. major TG44, respectively by 2'-C-methyladenosine treatment. The direct comparison of virus-positive and -negative strains by RNA-seq has revealed that LRV1 and LRV2 affect their respective hosts differently. While only 2 transcripts were found to be differentially expressed between L. guyanensis LRV1+ and LRV1-, this number in the case of L. major was substantially higher (67 up- and 20 down-regulated genes in LRV2- cells). The GO enrichment analysis has shown that they may be involved in numerous cell processes associated with nucleosome and DNA-protein complexes, while scrutiny of the KEGG pathways indicated that LRV2- L. major cells undergo autophagy. We concluded that in comparison to LRV1, LRV2 is more integrated into the Leishmania metabolism and its ablation is more detrimental for the host cells.
In addition, our analysis of the two viral genes, encoding the capsid and RNA-dependent RNA polymerase (RDRP), revealed them to be under the pressure of purifying selection, which was considerably stronger for the former gene across the whole tree. The selective pressure also differed between the LRV clades and correlated with the frequency of interspecific host switches. 
