Comparative Analysis of the Complete Plastomes of Apostasia wallichii and Neuwiedia singapureana (Apostasioideae) Reveals Different Evolutionary Dynamics of IR/SSC Boundary among Photosynthetic Orchids

Abstract

Apostasioideae, consists of only two genera, Apostasia and Neuwiedia, which are mainly distributed in Southeast Asia and northern Australia. The floral structure, taxonomy, biogeography, and genome variation of Apostasioideae have been intensively studied. However, detailed analyses of plastome composition and structure and comparisons with those of other orchid subfamilies have not yet been conducted. Here, the complete plastome sequences of Apostasia wallichii and Neuwiedia singapureana were sequenced and compared with 43 previously published photosynthetic orchid plastomes to characterize the plastome structure and evolution in the orchids. Unlike many orchid plastomes (e.g., Paphiopedilum and Vanilla), the plastomes of Apostasioideae contain a full set of 11 functional NADH dehydrogenase (ndh) genes. The distribution of repeat sequences and simple sequence repeat elements enhanced the view that the mutation rate of non-coding regions was higher than that of coding regions. The 10 loci—ndhA intron, matK-5′trnK, clpP-psbB, rps8-rpl14, trnT-trnL, 3′trnK-matK, clpP intron, psbK-trnK, trnS-psbC, and ndhF-rpl32—that had the highest degrees of sequence variability were identified as mutational hotspots for the Apostasia plastome. Furthermore, our results revealed that plastid genes exhibited a variable evolution rate within and among different orchid genus. Considering the diversified evolution of both coding and non-coding regions, we suggested that the plastome-wide evolution of orchid species was disproportional. Additionally, the sequences flanking the inverted repeat/small single copy (IR/SSC) junctions of photosynthetic orchid plastomes were categorized into three types according to the presence/absence of ndh genes. Different evolutionary dynamics for each of the three IR/SSC types of photosynthetic orchid plastomes were also proposed.

Plastome Evolution and Phylogeny of Orchidaceae, With 24 New Sequences

“…For examples, extensive gene losses have been reported in several independent mycoheterotrophic orchid lineages-i.e., Aphyllorchis (Feng et al, 2016), Cyrtosia (Kim et al, 2019), Epipogium (Schelkunov et al, 2015), Gastrodia (Yuan et al, 2018), Hexalectris (Barrett and Kennedy, 2018) and Rhizanthella (Delannoy et al, 2011). In addition, ndh deletion and pseudogenization are assumed to be phenomena that occur independently in many orchid lineages such as Apostasia (Lin et al, 2017;Niu et al, 2017a), Calypso , Cattleya (da Rocha Perini et al, 2016), Cephalanthera (Feng et al, 2016), Cremastra (Dong et al, 2018), Cymbidium (Yang et al, 2013;Kim et al, 2018;Wang et al, 2018), Dendrobium (Niu et al, 2017b), Epipactis (Dong et al, 2018), Eulophia (Huo et al, 2017), Holcoglossum (Li et al, 2019), Limodorum (Lallemand et al, 2019), Liparis (Krawczyk et al, 2018), Neuwiedia (Niu et al, 2017a), Oncidium (Wu et al, 2010;Kim et al, 2015a), Paphiopedilum (Niu et al, 2017b;Hou et al, 2018), Phalaenopsis (Chang et al, 2006), Phragmipedium (Kim et al, 2015a), Platanthera (Dong et al, 2018), Vanilla (Lin et al, 2015), and Vanda (Li et al, 2019). On the other hand, full ndh genes have been reported in members of Anoectochilus (Yu et al, 2016), Calanthe (Dong et al, 2018), Cypripedium (Kim et al, 2015b;Lin et al, 2015), Habenaria…”

The complete plastid genomes of Ophrys iricolor and O. sphegodes (Orchidaceae) and comparative analyses with other orchids

“…In contrast to these four tribes, large rearrangements in gene order have been found in the supposed basal smaller tribe of Apostasioideae. However, under the assumption that the common plastid types observed in most orchids represent the primitive state, it is likely that the rearrangements found in Apostasia wallichii and Apostasia odorata (but not in the related Neuwiedia [ 59 ]) may be due to recent, terminal autoapomorphic changes rather than being representative of the ancestral gene order of the orchid family.…”

Plastome-wide comparison reveals new SNV resources for the authentication of Dendrobium huoshanense and its corresponding medicinal slice (Huoshan Fengdou)

“…Furthermore, after intensive processing, the medicinal slices of Dendrobium species become more difficult to distinguish 44 . Recently, well-developed molecular marker techniques, i.e ., SSR, ISSR, AFLP and DNA barcodes became available for the identification of medicinal plants 9 , 10 , 11 , 45 , 46 , 47 , 48 , 49 . However, these methods can only be used to distinguish fresh Dendrobium materials, but are useless for their medicinal slices due to two reasons.…”