The Chloroplast Phylogenomics and Systematics of Zoysia (Poaceae)

Poaceae Chloroplast Genome Sequencing: Great Leap Forward in Recent Ten Years

The first complete chloroplast genome of rice (Oryza sativa) was published in 1989, ushering in a new era of studies of chloroplast genomics in Poaceae. Progresses in Next-Generation Sequencing (NGS) and Third-Generation Sequencing (TGS) technologiesand in the development of genome assembly software, have significantly advanced chloroplast genomics research. Poaceae is one of the most targeted families in chloroplast genome research because of its agricultural, ecological, and economic importance. Over the last 30 years, 2,050 complete chloroplast genome sequences from 40 tribes and 282 genera have been generated, most (97%) of them in the recent ten years. The wealth of data provides the groundwork for studies on species evolution, phylogeny, genetic transformation, and other aspects of Poaceae chloroplast genomes. As a result, we have gained a deeper understanding of the properties of Poaceae chloroplast genomes. Here, we summarize the achievements of the studies of the Poaceae chloroplast genomes and envision the challenges for moving the area ahead.

Disjunction and Vicariance Between East and West Asia: A Case Study on Euonymus sect. Uniloculares Based on Plastid Genome Analysis

Scientists have long been captivated by biogeographic disjunctions, and disjunctions between East Asia and North America have been particularly well-studied at the genus and family levels. By contrast, disjunctions between eastern and western Asia have received less attention. Euonymus L. is taxonomically divided into two sections based on the number of cells in anthers as follows: E. sect. Uniloculares has one-celled anthers and occurs mainly in Asia, whereas E. sect. Biloculares has two-celled anthers and is distributed globally. We used Illumina sequencing to investigate the genomes of four species in sect. Uniloculares. The chloroplast (cp) genomes are highly conserved (157,290-158,094 bp). Pseudogenisation of ndhF and intron loss in rps16 was detected. Based on the cp genomes of the four species of E. sect. Uniloculares, we propose a novel hypothesis of disjunction between eastern and western Asia. Biogeographic reconstruction and molecular dating revealed that sect. Uniloculares separated from its sect. Biloculares forebears 4.0 Mya during the Pliocene era. The radial diversification of sect. Uniloculares from East Asia and the establishment of the western Asian clade during the Pleistocene era (1.9 Mya) were the results of both dispersal and vicariance, making the section the youngest diverged clade conforming to age estimation. The centre of origin of sect. Uniloculares was determined to be in East Asia. Disjunctions and diversification between eastern and western Asia in sect. Uniloculares are thought to have been caused by changes in monsoon patterns, temperature variations, and the emergence of the Gobi Desert.

Phylogeny of Maleae (Rosaceae) Based on Complete Chloroplast Genomes Supports the Distinction of Aria, Chamaemespilus and Torminalis as Separate Genera, Different from Sorbus sp

Several genera formerly contained within the genus Sorbus L. sensu lato have been proposed as separate taxa, including Aria, Chamaemespilus and Torminalis. However, molecular evidence for such distinctions are rather scarce. We assembled the complete chloroplast genome of Sorbus aucuparia, another representative of Sorbus s.s., and performed detailed comparisons with the available genomes of Aria edulis, Chamaemespilus alpina and Torminalis glaberrima. Additionally, using 110 complete chloroplast genomes of the Maleae representatives, we constructed the phylogenetic tree of the tribe using Maximum Likelihood methods. The chloroplast genome of S. aucuparia was found to be similar to other species within Maleae. The phylogenetic tree of the Maleae tribe indicated that A. edulis, C. alpina and T. glaberrima formed a concise group belonging to a different clade (related to Malus) than the one including Sorbus s.s. (related to Pyrus). However, Aria and Chamaemespilus appeared to be more closely related to each other than to Torminalis. Our results provide additional support for considering Aria, Chamaemespilus and Torminalis as separate genera different from Sorbus s.s.