Dissecting the Satellite DNA Landscape in Three Cactophilic Drosophila Sequenced Genomes

Eukayote genomes are replete with repetitive DNAs. This class includes tandemly repeated satellite DNAs (satDNA) which are among the most abundant, fast evolving (yet poorly studied) genomic components. Here, we used high throughput sequencing data from three cactophilic Drosophila species, D. buzzatii, D. seriema and D. mojavensis, to access and study their whole satDNA landscape. In total, the RepeatExplorer software identified five satDNAs, three previously described (pBuM, DBC-150 and CDSTR198) and two novel ones (CDSTR138 and CDSTR130). Only pBuM is shared among all three species. The satDNA repeat length falls within only two classes, between 130-200bp or between 340-390bp. FISH on metaphase and polytene chromosomes revealed the presence of satDNA arrays in at least one of the following genomic compartments: centromeric, telomeric, subtelomeric or dispersed along euchromatin. The chromosomal distribution ranges from a single chromosome to almost all chromosomes of the complement. Fiber-FISH and sequence analysis of contigs revealed interspersion between pBuM and CDSTR130 in the microchromosomes of D. mojavensis. Phylogenetic analyses showed that the pBuM satDNA underwent concerted evolution at both interspecific and intraspecific levels. Based on RNAseq data, we found transcription activity for pBuM (in D. mojavensis) and CDSTR198 (in D. buzzatii) in all five analyzed developmental stages, most notably in pupae and adult males. Our data revealed that cactophilic Drosophila present the lowest amount of satDNAs (1.9% to 2.9%) within the Drosophila genus reported so far. We discuss how our findings on the satDNA location, abundance, organization and transcription activity may be related to functional aspects.

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