Comparative genomics reveals the presence of simple sequence repeats in genes related to virulence in plant pathogenic Pythium ultimum and Pythium vexans

In this study, we evaluated the occurrence, relative abundance (RA), and density (RD) of simple sequence repeats (SSRs) in the complete genome and transcriptomic sequences of the plant pathogenic species of Pythium to acquire a better knowledge of their genome structure and evolution. Among the species, P. ultimum had the highest RA and RD of SSRs in the genomic sequences, whereas P. vexans had the highest RA and RD in the transcriptomic sequences. The genomic and transcriptomic sequences of P. aphanidermatum showed the lowest RA and RD of SSRs. Trinucleotide SSRs were the most prevalent class in both genomic and transcriptomic sequences, while dinucleotide SSRs were the least prevalent. The G + C content of the transcriptomic sequences was found to be positively correlated with the number (r = 0.601) and RA (r = 0.710) of SSRs. A motif conservation study revealed the highest number of unique motifs in P. vexans (9.9%). Overall, a low conservation of motifs was observed among the species (25.9%). A gene enrichment study revealed P. vexans and P. ultimum carry SSRs in their genes that are directly connected to virulence, whereas the remaining two species, P. aphanidermatum and P. arrhenomanes, harbour SSRs in genes involved in transcription, translation, and ATP binding. In an effort to enhance the genomic resources, a total of 11,002 primers from the transcribed regions were designed for the pathogenic Pythium species. Furthermore, the unique motifs identified in this work could be employed as molecular probes for species identification.