Characterization of Two Satellite DNA Families in the Genome of the Oomycete Plant Pathogen Phytophthora parasitica .

Satellite DNA is a class of repetitive sequences that are organized in long arrays of tandemly repeated units in most eukaryotes. Long considered as selfish DNA, satellite sequences are now proposed to contribute to genome integrity. Despite their potential impact on the architecture and evolution of the genome, satellite DNAs have not been investigated in oomycetes due to the paucity of genomic data and the difficulty of assembling highly conserved satellite arrays. Yet gaining knowledge on the structure and evolution of genomes of oomycete pathogens is crucial to understanding the mechanisms underlying adaptation to their environment and to proposing efficient disease control strategies. Ade novoassembly of the genome ofPhytophthora parasitica, an important oomycete plant pathogen, led to the identification of several families of tandemly repeated sequences varying in size, copy number, and sequence conservation. Among them, two abundant families, designated asPpSat1andPpSat2, displayed typical features of satellite DNA and were collectively designated asPpSat. These two satellite families differ by their length, sequence, organization, genomic environment, and evolutionary dynamics.PpSat1, but notPpSat2, presented homologs among oomycetes. This observation, as well as the characterization of transcripts ofPpSatfamilies, suggested that these satellite DNA families likely play a conserved role within this important group of pathogens.