Comparative SNP Analysis of Chloroplast Genomes and 45S nrDNAs Reveals Genetic Diversity of Perilla Species

Perilla species belong to the Lamiaceae family of flowering plants and are widely grown in East Asia, for use in a traditional herbal medicine or functional food. To identify single nucleotide polymorphisms (SNPs) in Perilla species and conduct a phylogenomic analysis, we determined the complete sequences of the chloroplast (cp) genome and 45S nuclear ribosomal DNA (45S nrDNA) of six cultivated and three wild Perilla species. The complete cp genome ranged in size from 152,588 bp to 152,656 bp and the length variation in cp genomes was 68 bp. The length of the 45S nrDNA ranged from 6,235 bp to 8,303 bp and the main variation of length differences was in the intergenic spacer (IGS) region. Comparative analysis of the cp genome sequences of nine Perilla species showed low genetic diversity at the intra- and inter-species level. Using SNP analysis, we detected 42 synonymous SNPs (sySNPs) from 27 genes and 37 non-synonymous SNPs (nsSNPs) from 15 genes. A comparison of the 45S nrDNA sequences revealed two SNPs in the 18S rRNA, five SNPs in the 26S rRNA, three SNPs and two InDels in the internal transcribed spacer (ITS) 1 region, and six SNPs in the ITS 2 region. Our phylogenomic analysis suggests that the tetraploidization of Perilla cultivars may have arisen from the P. citriodora genome. The genotyping data from this study may be used to develop molecular markers associated with useful traits for use in Perilla breeding.