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Acta Prataculturae Sinica ›› 2024, Vol. 33 ›› Issue (4): 171-185.DOI: 10.11686/cyxb2023192

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Chloroplast genome assembly and phylogenetic analysis of Pholidota chinensis and Pholidota cantonensis

Bao-cai LIU1,2,3(), Xue-bo HU2, Wu-jun ZHANG1,3, Yun-qing ZHAO1,3, Ying-zhen HUANG1,3, Jing-ying CHEN1,3()   

  1. 1.Institute of Crop Sciences,Fujian Academy of Agricultural Sciences,Fuzhou 350003,China
    2.College of Plant Science and Technology,Huazhong Agricultural University,Wuhan 430070,China
    3.Research Center for Medicinal Plant,Fujian Academy of Agricultural Sciences,Fuzhou 350003,China
  • Received:2023-06-09 Revised:2023-08-04 Online:2024-04-20 Published:2024-01-15
  • Contact: Jing-ying CHEN

Abstract:

Pholidota chinensis and Pholidota cantonensis are rare and endangered epiphytic orchids. Little is known about their chloroplast genome sequences and phylogeny, so the aim of this study was to reveal their chloroplast genome characteristics and phylogenetic relationships. Young leaves of domesticated P. chinensis and P. cantonensis were collected in May 2022, and DNA was extracted and then sequenced using the Illumina sequencing platform. Bioinformatic analyses revealed that the chloroplast genomes included repetitive sequences and quartet boundaries, and showed codon biases. Chloroplast DNA sequences from related species were downloaded from the NCBI for genome comparison and phylogeny analyses. The chloroplast genomes of P. chinensis and P. cantonensis were 159122 bp (37.41% GC content) and 158798 bp (37.47% GC content) in length, respectively. They both included a large single-copy region (LSC), a small single-copy region (SSC), and an inverted repeat sequence (IRa/IRb). The relative synonymous codon usage of UUA encoding leucine reached 1.90 in P. chinensis and 1.91 in P. cantonensis. The chloroplast genome of P. chinensis had 44 simple sequence repeats, 47 scattered repeats, and 26 tandem repeats. The chloroplast genome of P. cantonensis had 32 simple sequence repeats, 25 scattered repeats, and 30 tandem repeats. The quartet boundaries and covariance of the six species in the Pholidota showed no large block variations, but some nucleotide polymorphisms were detected. Genes including trnK-UUU, trnQ-UUG, and rpl16 were identified as candidate genes for molecular markers of these species. A systematic analysis clarified that, although P. chinensis and P. cantonensis are in the genus Pholidota, they are more closely related to Bulleyia yunnanensis and Coelogyne fimbriata, and are located on the same branch of epiphytic orchids in the phylogenetic tree. The inversion of large segments of the chloroplast genome might be one of the reasons for the different growth habits of members of the Orchidaceae, and their ability to adapt to different habitats. The results of this study reveal the characteristics of the chloroplast genomes of P. chinensis and P. cantonensis, and provide new information about the relationship between their phylogeny and growth habits. These findings lay the foundation for further research on the classification of members of the Orchidaceae, as well as for molecular marker development and other related research.

Key words: Pholidota chinensis, Pholidota cantonensis, chloroplasts, genome, phylogeny, epiphytes