Comparative Analyses of Five Complete Chloroplast Genomes from the Genus Pterocarpus (Fabacaeae)

Abstract

Pterocarpus is a genus of trees mainly distributed in tropical Asia, Africa, and South America. Some species of Pterocarpus are rosewood tree species, having important economic value for timber, and for some species, medicinal value as well. Up to now, information about this genus with regard to the genomic characteristics of the chloroplasts has been limited. Based on a combination of next-generation sequencing (Illumina Hiseq) and long-read sequencing (PacBio), the whole chloroplast genomes (cp genomes) of five species (rosewoods) in Pterocarpus (Pterocarpus macrocarpus, P. santalinus, P. indicus, P. pedatus, P. marsupium) have been assembled. The cp genomes of five species in Pterocarpus have similar structural characteristics, gene content, and sequence to other flowering plants. The cp genomes have a typical four-part structure, containing 110 unique genes (77 protein coding genes, 4 rRNAs, 29 tRNAs). Through comparative genomic analysis, abundant simple sequence repeat (SSR)loci (333–349) were detected in Pterocarpus, among which A /T single nucleotide repeats accounted for the highest proportion (72.8–76.4%). In the five cp genomes of Pterocarpus, eight hypervariable regions, including trnH-GUG_psbA, trnS-UGA_psbC, accD-psaI, ndhI-exon2_ndhI-exon1, ndhG_ndhi-exon2, rpoC2-exon2, ccsA, and trnfM-CAU, are proposed for use as DNA barcode regions. In the comparison of gene selection pressures (P. santalinus as the reference genome), purifying selection was inferred as the primary mode of selection in maintaining important biological functions. Phylogenetic analysis shows that Pterocarpus is a monophyletic group. The species P. tinctorius is resolved as early diverging in the genus. Pterocarpus was resolved as sister to the genus Tipuana.

Isolation and characterization of microsatellite markers for the threatened African endemic tree species Pterocarpus erinaceus Poir.

“…Contrary to Hong et al. (2020) results in chloroplast genomes of five Pterocarpus species, among the single sequence repeats identified there was no single‐nucleotide repeats motifs accounted. The observed proportion of dinucleotide, trinucleotide, and tetranucleotide were respectively 30.1%, 25.3%, and 24.3%, while the tetranucleotide proportion was 2.27%.…”

“…More recently, in order to facilitate population identification and biodiversity protection, Hong et al. (2020) have sequenced and analyzed the whole chloroplast genomes of five Pterocarpus species: P. macrocarpus, P. santalinus, P. indicus, P. pedatus, and P. marsupium . This study has also led to the description of chloroplastic SSR.…”

Comparative plastid genomics of four Pilea (Urticaceae) species: insight into interspecific plastid genome diversity in Pilea

“…The protein-coding regions are highly conserved in plastid genomes [33]. We analyzed the protein-coding sequences of 79 identified unique orthologous genes in 4 Pilea taxa.…”

Comparative Plastid Genomics of Four Pilea (Urticaceae) Species: Insight into Interspecific Plastid Genome Diversity in Pilea

“…The protein-coding regions are highly conserved in plastid genomes [33]. We analyzed the protein-coding sequences of 79 identi ed unique orthologous genes in 4 Pilea taxa.…”