Plastome of Passiflora tripartiva var. mollisima
The plastid genome sequences of
P. tripartita var.
mollissima (poro-poro) (
Figure 1) was 163,451 bp in length, with a typical quadripartite structure consisting of a large single-copy (LSC) region of 85,525 bp (52.32% in total) and a small single-copy (SSC) region of 13,518 bp (8.27%), separated by a pair of inverted repeat regions (IRa and IRb) of 32,204 bp (19.70%). The poro-poro plastome is 12,045 bp longer than that of one of the most economically important species, passion fruit (
P. edulis) [
19], and is only 7,117 bp longer than that of the longest Passiflora plastome reported, i.e., P. arbelaezii [
24]. The plastome sequence of poro-poro has a
similar quadripartite architecture to other plants [
26,
27,
28]. However, the LSC region is 4,150 bp longer than that of
P. xishuangbannaensis but is 98bp, 195 bp, and 1,927 bp shorter than that of
P. caerulea, P. edulis, and
P. arbelaezii, respectivety. The SSC region is 121 bp, 140 bp, 359 bp, and 754 bp longer than that of
P. caerulea,
P. edulis,
P. xishuangbannaensis, and
P. arbelaezii, respectively. The IRs regions are 6,024 bp, 6,050 bp, and 11,600 longer than that of
P. caerulea,
P. edulis, and
P. xishuangbannaensis, respectively; however, it is 2,972 bp shorter than that of
P. arbelaezii [
19,
20,
21,
24]. The plastome structure of the
P. tripartita var.
mollissima consisted of A = 30.79%, T(U) = 32.34%, C = 18.67% and G = 18.20%. The overall AT content of the plastid genome was 63.13%, whereas the overall GC content was 36.87% as similar to that of other reported chloroplast genomes from the same family, such as 36.90% in
P. arbelaezii [
24], 37% in
P. edulis and
P. serrulata [
19,
22], 37.03% in
P. caerulea [
21], and 37.1% in
P. xishuangbannaensis [
20].
Poro-poro plastid genome annotation identified 128 genes, of which 112 were unique, and 17 were duplicated in the inverted repeat (IR) region. The plastome contained 84 protein-coding genes, 37 transfer RNA (tRNA)-coding genes, 7 ribosomal RNA (rRNA)-coding genes, and 14 genes with introns (12 genes with one intron and 2 genes with two introns), as shown in
Table 1. The poro-poro plastid genome contained 112 unique genes, of which there were 29 tRNA genes, 4 rRNA genes, and 79 protein-coding genes. The latter comprised 20 ribosomal subunit genes (9 large subunits and 11 small subunit), 4 DNA-directed RNA polymerase genes, 46 genes were involved in photosynthesis (11 encoded subunits of the NADH oxidoreductase, 7 for photosystem I, 15 for photosystem II, 6 for the cytochrome b6/f complex, 6 for different subunits of ATP synthase, and 1 for the large chain of ribulose biphosphate carboxylase), 8 genes were involved in different functions, and one gene was of unknown function (
Table 2).
In the plastid genome, 14 genes contained introns distributed as follows: the LSC, SSC, and IRs regions contained 8 genes (petD, rpl16, rpoC1, trnG-UCC, trnK-UUU, trnL-UAA, trnV-UAC, and ycf3), 1 gene (ndhA), and 5 genes (ndhB, rpl2, rps12, trnA-UGC, and trnI-GAU) respectively. Similarly, these genes included six protein-coding genes, each with a single intron (petD, ndhA, ndhB, rpoC1, rpl2, and rpl16); six tRNA genes, each with a single intron (trnA-UGC, trnG-UCC, trnI-GAU, trnK-UUU, trnL-UAA, and trnV-UAC); and two protein-coding genes with two introns (ycf3 and rps12). Except for 17 genes that were duplicated in the IR region (ndhB, rps19, rpl2, rpl23, rps12, ycf15, rrn5, rrn16, rrn23, trnA-UGC, trnI-CAU, trnI-GAU, trnL-CAA, trnM-CAU, trnN-GUU, trnR-ACG, and trnV-GAC) all genes contained a single copy, as shown in
Table 2. The plastome of
P. tripartita var.
mollissima contained eight genes (ycf1, ycf2, ycf15, rps16, rpl20, rpl22, accD, infA) that were lost or non-functional genes in P. edulis; and compared to
P. edulis, it has one absent gene (trnfM-CAU), as previously reported [
19]. In this study, the ycf1 sequence encodes a protein essential for plant viability and a vital component of the translocon on the inner chloroplast membrane (TIC) complex [
29], and ycf2 is a component of the ATPase motor protein associated with the TIC complex [
30].
Phylogenetic Reconstruction
To identify the evolutionary position of
Passiflora tripartita var.
mollissima in the Passifloraceae family, phylogenetic relationships based on the OrthoFinder clustering method were used to avoids erroneous rearrangements in phylogenetic tree reconstruction and provides a more reliable evolutionary analysis [
31,
32]. The phylogenetic tree was constructed based on single-copy orthologous genes [
33] and maximum likelihood analysis with the complete annotated protein sequences of 27 plastid genomes, of which 26 were from
Passiflora species. One species,
Vitis vinifera, was chosen as the outgroup,
Maximum likelihood (ML) bootstrap values ranged from 38%–92% for 7 of the 25 nodes. All nodes except the indicated ones (seven nodes) exhibited bootstrap support (BS) values of 100%. These
Passiflora species were divided into four groups: subgenus Passiflora (
P. nitida,
P. quadrangularis,
P. cincinnata,
P. caerulea,
P. edulis,
P. laurifolia,
P. vitifolia,
P. serratifolia,
P. serrulata,
P. ligularis,
P. serratodigitata,
P. actinia,
P. menispermifolia and
P. oerstedii), subgenus Tetrapathea (
P. tetrandra), subgenus Decaloba (
P. microstipula,
P. xishuangbannaensis,
P. biflora,
P. lutea,
P. jatunsachensis,
P. suberosa and
P. tenuiloba), and subgenus Deidamoides (
P. contracta and
P. arbelaezii). The relationships between the four subgenera of
Passiflora species (Passiflora, Tetrapathea, Decaloba, and Deidamoides) were congruent and strongly supported by the same patterns as previously reported [
34,
35]. These results resolved
Passiflora tripartita var.
mollissima was placed in the subgenus
Passiflora, which was closely related to
P. menispermifolia and
P. oerstedii with 100% BS, and was sister to
P. tetrandra (subgenus Tetrapathea),
P. biflora (subgenus Decaloba), and
P. contracta (subgenus Deidamoides), as shown in the cladogram (
Figure 2).