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Apostasia shenzhenica belongs to the subfamily Apostasioideae and is a primitive group located at the base of the Orchidaceae phylogenetic tree. However, the A. shenzhenica mitochondrial genome (mitogenome) is still unexplored, and the phylogenetic relationships between monocots mitogenomes remain unexplored. In this study, we discussed the genetic diversity of A. shenzhenica and the phylogenetic relationships within its monocotyledon mitogenome. We sequenced and assembled the complete mitogenome of A. shenzhenica, resulting in a circular mitochondrial draft of 672,872 bp, with an average read coverage of 122× and a GC content of 44.4%. A. shenzhenica mitogenome contained 36 protein-coding genes, 16 tRNAs, two rRNAs, and two copies of nad4L. Repeat sequence analysis revealed a large number of medium and small repeats, accounting for 1.28% of the mitogenome sequence. Selection pressure analysis indicated high mitogenome conservation in related species. RNA editing identified 416 sites in the protein-coding region. Furthermore, we found 44 chloroplast genomic DNA fragments that were transferred from the chloroplast to the mitogenome of A. shenzhenica, with five plastid-derived genes remaining intact in the mitogenome. Finally, the phylogenetic analysis of the mitogenomes from A. shenzhenica and 28 other monocots showed that the evolution and classification of most monocots were well determined. These findings enrich the genetic resources of orchids and provide valuable information on the taxonomic classification and molecular evolution of monocots.

Seed plants comprise angiosperms and gymnosperms. The latter includes gnetophytes, cycads, Ginkgo, and conifers. Conifers are distributed worldwide, with 630 species distributed across eight families and 70 genera. Their distinctiveness has triggered much debate on their origin, evolution, and phylogenetic placement among seed plants. To better understand the evolution of gymnosperms and their relation to other seed plants, we report here a high-quality genome sequence for a tree species, Chinese fir (Cunninghamia lanceolata), which has excellent timber quality and high aluminum adaptability and is a member of Cupressaceae with high levels of heterozygosity. We assembled an 11.24 Gb genome with a contig N50 value of 2.15 Mb and anchored the 10.89 Gb sequence to 11 chromosomes. Phylogenomic analyses showed that cycads sister to Ginkgo, which place to sister in all gymnosperm lineages, and Gnetales within conifers sister to Pinaceae. Whole-genome duplication (WGD) analysis showed that the ancestor of seed plants has differentiated into angiosperms and gymnosperms after having experienced a WGD event. The ancestor of extant gymnosperm has experienced a gymnosperm-specific WGD event and the extant angiosperms do not share a common WGD before their most recent common ancestor diverged into existing angiosperms lineages. Analysis of the MADS-box gene family ofC. lanceolatarevealed the developmental mechanism of the reproductive organs inC. lanceolata, which supported the (A)B(C) model of the development of gymnosperms reproductive organs. In addition, astringent seeds and shedding of whole branches (with withered leaves) might be a strategy ofC. lanceolatathat evolved during long-term adaptation to an aluminum-rich environment. The findings also reveal the molecular regulation mechanism of shade tolerance inC. lanceolataseedlings. Our results improve the resolution of ancestral genomic features within seed plants and the knowledge of genome evolution and diversification of gymnosperms.

Ludisia discolor is one of the most important ornamental and medicinal orchids. To improve our understanding of the evolution of chloroplast, we resequenced complete chloroplast (cp) genome of L. discolor from Hainan, China. The cp genome sequence of L. discolor of Hainan was 153,324 bp in length, with a large single-copy (LSC) region of 82,922 bp, a small single-copy (SSC) region of 17,258 bp, and a pair of inverted repeats (IR) regions of 26,572 bp. Complete chloroplast genome contain 132 genes, there were 86 protein-coding genes, 38 tRNA genes and eight rRNA genes. The phylogenetic tree showed that L. discolor of Hainan is sister to L. discolor (unknown distributed region). Their cp genomes have same gene number but different in length of genome, indicating high conserved among them.

The mangrove Kandelia obovata (Rhizophoraceae) is an important coastal shelterbelt and landscape tree distributed in tropical and subtropical areas across East Asia and Southeast Asia. Herein, a chromosome-level reference genome of K. obovata based on PacBio, Illumina, and Hi-C data is reported. The high-quality assembled genome size is 177.99 Mb, with a contig N50 value of 5.74 Mb. A large number of contracted gene families and a small number of expanded gene families, as well as a small number of repeated sequences, may account for the small K. obovata genome. We found that K. obovata experienced two whole-genome polyploidization events: one whole-genome duplication shared with other Rhizophoreae and one shared with most eudicots (γ event). We confidently annotated 19,138 protein-coding genes in K. obovata and identified the MADS-box gene class and the RPW8 gene class, which might be related to flowering and resistance to powdery mildew in K. obovata and Rhizophora apiculata, respectively. The reference K. obovata genome described here will be very useful for further molecular elucidation of various traits, the breeding of this coastal shelterbelt species, and evolutionary studies with related taxa.

Orchids are of special interest to plant conservationists because of their high species diversity as well as their obligate dependencies on one or more biotic interactions, which often pose additional challenges in their conservation. In this study, we analyze threats to all known Chinese orchid species and evaluate whether current in situ and ex situ conservation efforts match these threats. Of the 1582 orchids included in this study, 653 (43.5%) were categorized as threatened (i.e., critically endangered, endangered, or vulnerable), 191 (12.0%) were traded using wild-collected plants, 531 (33.6%) were Chinese endemics, 826 (52.2%) were found in one or more protected areas, 802 (50.7%) were in ex-situ collections, 136 (8.4%) had seeds in storage; and only 43 (2.7%) were subject to conservation translocation actions within China. Proportionally, more threatened species were protected in situ and ex situ than non-threatened species. However, the current version of the Chinese Redlist assessment assigned over harvesting as a threat factor to 15 Chinese orchids only (2.3%), a gross underestimation of this threat considering both the Chinese and international orchid markets. We propose establishing small nature reserves to protect wild orchid species that do not currently occur in any protected area, creating ex situ collection networks to strengthen conservation capacity (including institutions that are concerned with utilization only), and establishing a dynamic list of wild orchids in trade, along with trade volumes, to better-gauge conservation threats posed by wild harvest.