# Conserved Plastid Genomes of _Pourthiaea_ Trees: Comparative Analyses and Phylogenetic Relationship
## 3 Results  
### Plastome Structure  
We obtained at least 3.0 Gb of raw reads for _Pourthiaea beauverdiana_ (24,239,328 reads), _Pourthiaea parifolia_ (22,662,706 reads), _Pourthiaea villosa_ (24,516,204 reads), and _Photitia glomera_ (23,435,210 reads) through Illumina NovaSeq sequencing (Table 1). We used 24,062,356 clean reads for _P. beauverdiana_, 22,404,606 clean reads for _P. parvifolia_, 24,214,064 clean reads for _P. villosa_, and 23,321,484 clean reads for _Ph. glomera_ to assemble the complete plastid genomes with the mean coverage depth ranging from 61.31\(\times\) (_P. parvifolia_) to 214.50\(\times\) (_Ph. glomera_) (Table 1).  
The plastomes of three _Pourthiaea_ species shared typical quadripartite structures, ranging from 159,903 bp (_P. parvifolia_) to 160,090 bp (_P. beauverdiana_) (Table 2). The three plastomes contained a pair of IRs (26,394-26,399 bp), separated by a SSC region (19,304-19,322 bp) and a LSC region (87,811-87,973 bp) (Table 2). A total of 113 unique genes were predicted for the plastomes of the three _Pourthiaea_ species, including four rRNA genes, 30 tRNA genes, and 79 PCGs (Table 2). The three plastomes had eighteen genes replicated in both IR regions, comprising four rRNA genes (_rrn_5, _rrn_4.5, _rrn_16, and _rrn_23), seven tRNA genes (_trn_I-CAU, _trn_R-ACG, _trn_A-UGC, _trn_I-GAU, _trn_I-CAA, _trn_V-GAC, and _trn_N-GUU), and seven PCGs (_rps12, rpl23, rpl2, rps7, vcf1, vcf2, and _ndh_B) (Figure 1; Tables 2 and S2). The GC content of _P. beauverdiana_ and _P. villosa_ was 36.5%, while the GC content of _P. parvifolia_ was 36.6% (Table 2). The plastome of _Ph. glomera_ was similar to the other three _Pourthiaea_ species, being 160,261 bp in length and containing 113 unique genes. The overall GC content of the _Ph. glomera_ plastome was 36.4% (Figure S1; Tables 2 and S2).  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Species** & **Total Size** & **LSC** & **SSC** & **IR** & **Unique Gene** & **PCGs** & **tRNA** & **rRNA** & **GC\%** \\ \hline  & **(bp)** & **(bp)** & **(bp)** & **(bp)** & **Numbers** & & & & \\ \hline _P. beauverdiana_ & 160,090 & 87,973 & 19,319 & 26,399 & 113 & 79 (7) & 30 (7) & 4 (4) & 36.5 \\ _P. parvifolia_ & 159,903 & 87,811 & 19,304 & 26,394 & 113 & 79 (7) & 30 (7) & 4 (4) & 36.6 \\ _P. villosa_ & 160,030 & 87,920 & 19,322 & 26,394 & 113 & 79 (7) & 30 (7) & 4 (4) & 36.5 \\ _Ph. glomera_ & 160,261 & 88,222 & 19,273 & 26,383 & 113 & 79 (7) & 30 (7) & 4 (4) & 36.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of the complete plastomes of three _Pourthiaea_ species and _Photitia glomera_.  
The IR/SC boundary regions were highly conserved among 13 _Pourthiaae_ plastomes (Figure 2). The LSC/IRb borders were situated in the _rps_19 genes and extended 120 bp into the _rps_19 genes. The _ycf_1 genes and _ndh_F genes were overlapped in the IRb/SSC regions, overlapping by 7 bp and 14 bp, respectively. The _ycf_1 genes crossed the SSC/IRa borders, with 4564 bp in the SSC regions and 1076 bp in the IRa regions. The IRa/LSC borders extended into the _rpl2-trm_H and were 190 bp and 5-145 bp away from the _rpl_2 genes and _trm_H genes, respectively.