Orchidaceae is the 3rd largest family of angiosperms, an evolved young branch of monocotyledons. This family contains a number of economically-important horticulture and flowering plants. However, the limited availability of genomic information largely hindered the study of molecular evolution and phylogeny of Orchidaceae. In this study, we determined the evolutionary characteristics of whole chloroplast (cp) genomes and the phylogenetic relationships of the family Orchidaceae. We firstly characterized the cp genomes of four orchid species: Cremastra appendiculata, Calanthe davidii, Epipactis mairei, and Platanthera japonica. The size of the chloroplast genome ranged from 153,629 bp (C. davidi) to 160,427 bp (E. mairei). The gene order, GC content, and gene compositions are similar to those of other previously-reported angiosperms. We identified that the genes of ndhC, ndhI, and ndhK were lost in C. appendiculata, in that the ndh I gene was lost in P. japonica and E. mairei. In addition, the four types of repeats (forward, palindromic, reverse, and complement repeats) were examined in orchid species. E. mairei had the highest number of repeats (81), while C. davidii had the lowest number (57). The total number of Simple Sequence Repeats is at least 50 in C. davidii, and, at most, 78 in P. japonica. Interestingly, we identified 16 genes with positive selection sites (the psbH, petD, petL, rpl22, rpl32, rpoC1, rpoC2, rps12, rps15, rps16, accD, ccsA, rbcL, ycf1, ycf2, and ycf4 genes), which might play an important role in the orchid species’ adaptation to diverse environments. Additionally, 11 mutational hotspot regions were determined, including five non-coding regions (ndhB intron, ccsA-ndhD, rpl33-rps18, ndhE-ndhG, and ndhF-rpl32) and six coding regions (rps16, ndhC, rpl32, ndhI, ndhK, and ndhF). The phylogenetic analysis based on whole cp genomes showed that C. appendiculata was closely related to C. striata var. vreelandii, while C. davidii and C. triplicate formed a small monophyletic evolutionary clade with a high bootstrap support. In addition, five subfamilies of Orchidaceae, Apostasioideae, Cypripedioideae, Epidendroideae, Orchidoideae, and Vanilloideae, formed a nested evolutionary relationship in the phylogenetic tree. These results provide important insights into the adaptive evolution and phylogeny of Orchidaceae.

Notopterygium incisum C. C. Ting ex H. T. Chang (Apiaceae) is an endangered perennial herb in China. The lack of transcriptomic and genomic resources for N. incisum greatly hinders studies of its population genetics and conservation. In this study, we employed RNA-seq technology to characterize transcriptomes for the flowers, leaves, and stems of this endangered herb. A total of 56 million clean reads were assembled into 120,716 unigenes with an N50 length of 850 bp. Among these unigenes, 70,245 (58.19%) were successfully annotated and 65,965 (54.64%) were identified as coding sequences based on their similarities with sequences in public databases. We identified 21 unigenes that had significant relationships with cold tolerance in N. incisum according to gene ontology (GO) annotation analysis. In addition, 13,149 simple sequence repeats (SSRs) and 85,681 single nucleotide polymorphisms were detected as potential molecular genetic markers. Ninety-six primer pairs of SSRs were randomly selected to validate their amplification efficiency and polymorphism. Nineteen SSR loci exhibited polymorphism in three natural populations of N. incisum. These results provide valuable resources to facilitate future functional genomics and conservation genetics studies of N. incisum.

Acer tsinglingense is an ecologically and economically important tree species in China. In this study, we characterized its whole plastid genome sequence using the Illumina sequencing platform. The complete plastid genome size of A. tsinglingense is 156,039 bp in length, including a large single-copy [LSC] region of 85,760 bp, a small single-copy [SSC] region of 18,139 bp, and a pair of inverted repeats [IRs] of 26,070 bp. The genome contains 137 genes, including 89 protein-coding genes, 40 tRNA genes, and 8 rRNA genes. The GC contents in chloroplast genome, LSC region, SSC region, and IR region were 38.0%, 36.2%, 32.4%, and 42.9%, respectively. The phylogenetic analysis based on the plastid genomes showed that A. tsinglingense was more closely related with the congeneric A. laevigatum, A. palmatum, A. wilsonii, and A. buergerianum, these species were clustered into a monophyletic clade with high bootstrap support.