*2.2. Comparison of the Basic Characteristics of the Chloroplast Genome in Five Pyrus Species*

The chloroplast genome of *Pyrus* is a typical ring structure 159,834–160,059 bp in length (Table 2). The chloroplast genome of *P. communis* L. cv. Early Red Comice is the shortest, and the longest is *P. ussuriensis* Maxin. cv. Jingbaili. The LSC length of *Pyrus* is 87,793–88,074 bp, the longest in *P. ussuriensis* Maxin. cv. Jingbaili and the shortest in *P. communis* L. cv. Early Red Comice. The SSC length is 19,201–19,261 bp, with the longest in *P. betulifolia* and the shortest in both genotypes of *P. hopeiensis*.



The IR regions were of similar length in four of the five *Pyrus* species, and only differed by 4 bp, except in *P. communis* L. cv. Early Red Comice. The GC content was similar, 36.57–36.59%. The number of protein-coding genes ranged from 74 to 78. The chloroplast genome of the five *Pyrus* species contained 15 genes, including introns (nine protein-coding genes and six tRNAs, see Table 3), and the *ycf3* gene contained two introns. The intron in *P. betulifolia* contained 13 genes, followed by 12 in *P. ussuriensis* Maxin. cv. Jingbaili, 11 in *P. hopeiensis* HB-1, 10 in *P. hopeiensis* HB-2, and 10 in *P. communis* L. cv. Early Red Comice. In the five *Pyrus* species, nine genes contained introns (*rpoC1*, *ycf3*, *rpl22*, *rpl2*, *ndhA*, *ndhB*, *rpl2*, *rps12*, and *rps12*), all of which were protein-coding genes. The intron in the *ndhA* gene was the longest, at 1125–1169 bp. Other than the short intron length of the *trnI-TAT* gene in *P. ussuriensis* Maxin. cv. Jingbaili, *rpl22* harbored the smallest intron of the other four *Pyrus* species, at 63–83 bp. The results showed that the size, structure, sequence, and GC content of the chloroplast genome of *P. hopeiensis* were similar to those of the other three *Pyrus* species, which was characteristic of the slow evolution of the genus *Pyrus* [7] in comparison to the chloroplast genomes of *P. hopeiensis*, *P. communis* L. cv. Early Red Comice, *P. ussuriensis* Maxin. cv. Jingbaili, and *P. betulifolia*.




**Table 3.** *Cont*.
