Discussion

Genome plasticity and its potential role in diversity in natural Leishmania populations have been a subject of several studies carried out on isolated and cultivated promastigotes. However, it is unknown whether the results obtained with in vitro parasites reflect the Leishmania genome dynamics in in vivo. In this study we addressed (i) whether genome diversity is generated and selected during the life cycle of L. donovani, and (ii) what is the impact of potential genomic changes on the transcriptome. The study was initiated with an aneuploid (8/36) field isolate of reference strain BPK282/0. We observed a minor decrease in aneuploidy (6/36) after the establishment of late stage infection in Phlebotomus argentipes, followed by further decrease in somy of one chromosome in amastigotes purified from golden hamster at the end of first passage (2 months). Interestingly, after consecutive 3 and 4 passages in golden hamsters, the aneuploidy pattern changed drastically with all trisomic chromosomes becoming disomic, and the chr8 emerging as trisomic. Thus, we conclude that aneuploidy pattern is flexible and environment-specific. The observed changes in chromosome copy number in each samples correlated with the amount of transcripts per chrosomome, with the exception of chr31. At the same time, when we compared the transcriptomes of amastigotes, and in vitro promastigotes characterised by identical low aneuploidy pattern, we found 9.6 % of the genes to be overexpressed in promastigotes, and only 3.2% in amastigotes. Therefore, the transcriptome is shaped by a complex interaction between genome dosage and stage-specific regulation of gene expression.