3 |
Results
3.1 | Basic characteristics
of chloroplast
genomes
This study obtained the complete chloroplast genome sequences of six
medicinal plants of Polygonatum : P. zanlanscianense ,P. kingianum , P. sibiricum , P. cyrtonema , P.
filipes and P. odoratum . The length of the complete chloroplast
genome sequences ranged from 154, 578 bp (P. odoratum ) to 155,
807 bp (P. kingianum ), with an average length of 155, 429 bp. ThePolygonatum chloroplast genome has a typical quadripartite
structure, including large single-copy (LSC), small single-copy (SSC),
and a pair of IR regions. The length of the LSC ranged from 83, 527 bp
(P. odoratum ) to 84, 626 bp (P. kingianum ). In the SSC
regions, the chloroplast genome of P. sibiricum was the shortest
(18, 415 bp) and P. kingianum was the longest (18, 529 bp). The
IR lengths ranged from 26, 297 bp for P. odoratum to 26, 415 bp
for P. zanlanscianense . GC content was unevenly distributed
across the four parts of the chloroplast genome. The total GC content of
the chloroplast genome was 37.7% and the GC contents in the LSC, SSC,
and IR regions were 35.7–35.8 %, 31.5–31.6 %, and 43 %,
respectively (Figure 1, Table 1).
Differences were observed in the number of chloroplast genome genes
among the six Polygonatum species. P. kingianum andP. filipes encoded 127 and 130 genes, respectively, whereas the
other species encoded 131 genes. These genes comprised 84–85
protein-coding genes, 37–38 transfer RNA genes and 6–8 ribosomal RNA
genes. The IR regions included seven protein-coding genes (rpl2 ,rpl23 , rps12 , rps19 , rps7 , ndhB , andycf2 ), 11 tRNA genes (trnG-UCC , trnE-UUC ,trnM-CAU , trnH-GUG , trnI-CAU , trnL-CAA ,trnV-GAC , trnI-GAU , trnA-UGC , trnR-ACG , andtrnN-GUU ), and all four rRNA-coding genes. A total of 22 genes in
the chloroplast genomes of the six Polygonatum species contained
introns ycf3 and clpP each containing two introns.rps12 , trnK-UUA , rps16 , trnG-UCC ,trnT-CGU , atpF , rpoC1 , trnL-UAA ,trnV-UAC , petB , petD , rpl16 , rpl2 ,ndhB , trnI-GAU , trnE-UUC , trnA-UGC , andndhA contained a single intron. trnT-CGU was annotated only
in P. kingianum, which lacked rrn4.5, rpoC1and trnV-UAC. ThendhB gene of P. kingianum did not contain introns.The ycf2 and ycf1 genes of P. zanlanscianense also
contained two introns, ycf2 gene of P. sibiricum andP. cyrtonema contained one intron, and P. kingianum ,P. filipes and P. odoratum had no introns. Gene and intron
losses occurred during the evolution of the six medicinal plants ofPolygonatum (Table 2).
TABLE 1 Basic chloroplast characteristics of six medicinal plants ofPolygonatum .