In order to understand the evolution of the orchid plastome, we annotated and compared 124 complete plastomes of Orchidaceae representing all the major lineages in their structures, gene contents, gene rearrangements, and IR contractions/expansions. Fortytwo of these plastomes were generated from the corresponding author's laboratory, and 24 plastomes-including nine genera (Amitostigma, Bulbophyllum, Dactylorhiza, Dipodium, Galearis, Gymnadenia, Hetaeria, Oreorchis, and Sedirea)-are new in this study. All orchid plastomes, except Aphyllorchis montana, Epipogium aphyllum, and Gastrodia elata, have a quadripartite structure consisting of a large single copy (LSC), two inverted repeats (IRs), and a small single copy (SSC) region. The IR region was completely lost in the A. montana and G. elata plastomes. The SSC is lost in the E. aphyllum plastome. The smallest plastome size was 19,047 bp, in E. roseum, and the largest plastome size was 178,131 bp, in Cypripedium formosanum. The small plastome sizes are primarily the result of gene losses associated with mycoheterotrophic habitats, while the large plastome sizes are due to the expansion of noncoding regions. The minimal number of common genes among orchid plastomes to maintain minimal plastome activity was 15, including the three subunits of rpl (14, 16, and 36), seven subunits of rps (2, 3, 4, 7, 8, 11, and 14), three subunits of rrn (5, 16, and 23), trnC-GCA, and clpP genes. Three stages of gene loss were observed among the orchid plastomes. The first was ndh gene loss, which is widespread in Apostasioideae, Vanilloideae, Cypripedioideae, and Epidendroideae, but rare in the Orchidoideae. The second stage was the loss of photosynthetic genes (atp, pet, psa, and psb) and rpo gene subunits, which are restricted to Aphyllorchis, Hetaeria, Hexalectris, and some species of Corallorhiza and Neottia. The third stage was gene loss related to prokaryotic gene expression (rpl, rps, trn, and others), which was observed in Epipogium, Gastrodia, Lecanorchis, and Rhizanthella. In addition, an intermediate stage between the second and third stage was observed in Cyrtosia (Vanilloideae). The majority of intron losses are associated with the loss of their corresponding genes. In some orchid taxa, however, introns have been lost in rpl16, rps16, and clpP(2) without their corresponding gene being lost. A total of 104 gene rearrangements were counted when comparing 116 orchid plastomes. Among them, many were concentrated near the IRa/b-SSC junction area. The plastome phylogeny of

Cyrtosia septentrionalis is an achlorophyllous mycoheterotrophic orchid in the subfamily Vanilloideae (Orchidaceae). This article reports C. septentrionalis ’s complete plastome sequence and compare it with other orchid plastomes with a same mycoheterotrophic nutritional mode. The C. septentrionalis plastome has decreased to 96,859 bp in length, but it still maintains a quadripartite structure. The C. septentrionalis plastome contains 38 protein-coding genes, 25 tRNA genes, and four ribosomal RNA genes. Most genes related to photosynthesis have been lost, whereas the majority of housekeeping genes remain; this pattern corresponds to the end of stage 3 gene degradation. The inverted repeat regions of the C. septentrionalis plastome have decreased to 10,414 bp and mainly contain the gene ycf 2. A block consisting of four rrn genes and rps 7 and rps 12 has shifted to a small single-copy region. As a result, the small single-copy region was found to be expanded, despite the loss of all ndh genes in the region. Three inversion mutations are required to explain the C. septentrionalis plastome’s current gene order. The species is endangered, and these results have implications for its conservation.

Lindera Thunb. (Lauraceae) consists of approximately 100 species, mainly distributed in the temperate and tropical regions of East Asia. In this study, we report 20 new, complete plastome sequences including 17 Lindera species and three related species, Actinodaphne lancifolia, Litsea japonica and Sassafras tzumu. The complete plastomes of Lindera range from 152,502 bp (L. neesiana) to 154,314 bp (L. erythrocarpa) in length. Eleven small inversion (SI) sites are documented among the plastomes. Six of the 11 SI sites are newly reported and they locate in rpoB-trnC, psbC-trnS, petA-psbJ, rpoA and ycf2 regions. The distribution patterns of SIs are useful for species identification. An average of 83 simple sequence repeats (SSRs) were detected in each plastome. The mono-SSRs accounted for 72.7% of total SSRs, followed by di- (12.4%), tetra- (9.4%), tri- (4.2%), and penta-SSRs (1.3%). Of these SSRs, 64.6% were distributed in an intergenic spacer (IGS) region. In addition, 79.8% of the SSRs are located in a large single copy (LSC) region. In contrast, almost no SSRs are distributed in inverted repeat (IR) regions. The SSR loci are useful to identifying species but the phylogenetic value is low because the majority of them show autapomorphic status or highly homoplastic characteristics. The nucleotide diversity (Pi) values also indicated the conserved nature of the IR region compared to LSC and small single copy (SSC) regions. Five spacer regions with high Pi values, trnH-psbA, petA-psbJ and ndhF-rpl32, rpl32-trnL and Ψycf1-ndhF, have a potential use for the molecular identification study of Lindera and related species. Lindera species form a paraphyletic group in the plastome tree because of the inclusion of related genera such as Actinodaphne, Laurus, Litsea and Neolitsea. A former member of tribe Laureae, Sassafras, forms a clade with the tribe Cinnamomeae. The SIs do not affect the phylogenetic relationship of Laureae. This result indicated that ancient plastome captures may have contribute to the mixed intergeneric relationship of Laureae. Alternatively, the result may indicate that the morphological characters defined the genera of Lauraceae originated for several times.

The complete plastome sequence of Garcinia mangostana L. (Clusiaceae) is completed in this study (NCBI acc. no. KX822787). This is a first complete plastome sequence from the Clusiaceae. The complete plastome size is 158,179 bp in length and consists of a large single copy of 86,458 bp and a small single copy of 17,703 bp, separated by two inverted repeats of 27,009 bp. The G. mangostana plastome shows four minor structural modifications including inf A gene loss, rpl 32 gene loss, ycf 3 gene intron loss and a 363 bp inversion between trn V-UAC and atp E gene. The plastome contains 111 genes, of which 77 are protein-coding genes, 30 are tRNA genes and four are rRNA genes. The average A-T content of the plastome is 63.9%. A total of 110 simple sequence loci are identified from the genome. Phylogenetic analysis reveals that G. mangostana is a sister group of Erythroxylum novogranatense (Erythroxylaceae) with 78% bootstrap support.

The complete plastome sequence of Durio zibethinus L. (Malvaceae) is determined in this study (NCBI acc. no. MG138151). D. zibethinus is an important fruit crop in Southeastern Asia and known as the 'king of fruit'. Our D. zibethinus plastome is the first reported sequences from the subfamily Helicteroideae of Malvaceae. The plastome sequence of D. zibethinus is 163,974 bp in length and it is composed of a pair of 23,679 bp inverted repeat regions separated by large and small single-copy regions of 95,704 bp and 20,912 bp, respectively. The gene order and structure of the D. zibethinus are similar to those of the typical plastome of land plants. The plastome encodes 113 genes, of which 79 are protein-coding genes, 30 are tRNA genes, and four are rRNA genes. Fifteen genes contain single intron and two genes have two introns. A total of 144 simple sequence repeats (SSR) were identified in the genome. Phylogenetic analysis show that D. zibethinus (Helicteroideae) is sister group of Tilia (Tilioideae) clade with 100% bootstrap support.

No abstract

In this study, we determined the complete plastome sequence of Averrhoa carambola L. (Oxalidaceae) (NCBI acc. no. KX364202). To the best of our knowledge, this is the first reported complete plastome sequence from the order Oxalidales. The gene order and structure of the A. carambola plastome are collinear with the typical plastome of land plants. The complete plastome size is 155,965 bp in length and consists of a large single copy region of 87,217 bp and a small single copy region of 17,496 bp, which are separated by a pair of 25,626-bp-long inverted repeat regions. The overall A-T content of the plastome sequence is 61.2%. The plastome contains 111 genes, of which 77 are protein-coding genes, 30 are tRNA genes, and 4 are rRNA genes. Sixteen genes contain one intron and two genes have two introns. A total of 91 simple sequence loci were identified from the genome. Phylogenetic analysis revealed that A. carambola is a sister group of Euonymus japonicus with 100% bootstrap support.

In this study, we determined the complete plastome sequence of Pouteria campechiana (Kunth) Baehni (Sapotaceae) (NCBI acc. no. KX426215). This is the first time a plastome from the Sapotaceae has been sequenced. The gene order and structure of the P. campechiana plastome are collinear with those of the typical plastome of land plants. The complete plastome size is 157,922 bp in length and consists of a large single-copy region of 87,122 bp and a small single-copy region of 18,559 bp, which are separated by a pair of 26,120 bp-long inverted repeat regions. The overall A–T content of the plastome sequence is 63.2%. The plastome contains 113 genes, of which 79 are protein-coding genes, 30 are tRNA genes, and 4 are rRNA genes. Sixteen genes contain one intron and two genes have two introns. A total of 91 simple sequence repeat loci were identified within the genome. Phylogenetic analysis revealed that P. campechiana is a sister group of the Primulaceae-Ebenaceae clade with 100% bootstrap support.