Search

Hibiscus mutabilis is native to China with a long cultivation history, and is an ancient garden tree species and medicinal plant. In this study, we selected three cultivars of H. mutabilis in a hybrid combination(H. mutabilis cv. Danbanbai, H. mutabilis cv. Jinqiusong, H. mutabilis cv. Mudanfen)to investigate evolutionary characteristics between the cultivars of H. mutabilis and its related species, and clarify the phylogenetic relationship between the cultivars of H. mutabilis and its related species, as well as explore the genetic model of chloroplast genome(cpDNA)of H. mutaibilis at the same time. We first sequenced the three cultivars of H. mutaibilis using Illumina NovaSeq. After assembly and annotation, three complete chloroplast genome sequences were obtained. The cpDNAs of the related species H. taiwanensis from our group, and H. syricus and H. rosa-sinensis from the gene bank. Then we carried out comparative analysis on composition and structure of cpDNAs of four species of Hibiscus and three cultivars of H. mutabilis, and completed its phylogenetic tree reconstruction. The results were as follows: (1)Total sizes of cpDNAs of H. mutabilis cv. Danbanbai, H. mutabilis cv. Jinqiusong, H. mutabilis cv. Mudanfen were 160 880, 160 879, 160 920 bp, respectively, and the total gene number was 130, including 85 protein-coding genes, eight ribosomal RNAs, and 37 transfer RNAs. (2) The comparative analyses showed that the cpDNAs of three cultivars of H. mutabilis and the related species H. taiwanensis were highly conserved, and the inverted repeat regions(IR)were all 26 300 bp; H. rosa-sinensis and H. syriacus shrank to at 25 745 and 25 598 bp, respectively.(3)The phylogenetic analysis revealed that the three cultivars were planted into a monophyletic branch, and then together with H. taiwanensis into a high support branch, indicating that H. mutabilis and H. taiwanensis had the closest relationship; Compared with H. syriacus and H. rosa-sinensis, H. mutabilis and H. taiwanensis were more closely related to H. hamabo, H. tiliaceum and H. canabinus.(4)Three cultivars of H. mutabilis could be distinguished by cpDNA sequence, the length of LSC/SSC of H. mutabilis cv. Danbanbai, H. mutabilis cv. Jinqiusong, H. mutabilis cv. Mudanfen were 89 355 bp/18 925 bp, 89 353 bp/18 926 bp, 89 400 bp/18 920 bp, respectively. And candidate molecular markers and DNA barcodes had been developed from repeat sequence and nucleotide diversity analyses, which could be used as a tool for cultivars identification.(5)The cpDNAs of H. mutabilis cv. Danbanbai and H. mutabilis cv. Jinqiusong showed a minimum difference and had the closest phylogenetic relationship. According to the relationship between their female and offspring, the maternal genetic characteristics of the cpDNAs of Hibiscus were proved. This study will help us to understand the evolutionary characteristics and phylogenetic relationship of cpDNAs of three cultivars of H. mutabilis and H. taiwanensis, and provide basic data on cpDNA for accurate identification of the cultivars of H. mutabilis and breeding of excellent cultivars. [ABSTRACT FROM AUTHOR]

Estimating the time scale of species evolution is an important part of life evolution study. It is found that there are significant differences in the evolution rates of different genes and species in recent years, which challenges the molecular clock hypothesis to a great extent. Therefore, new methods are needed to re-estimate the evolutionary event time. The whole genome sequence of angiosperms makes it possible to estimate the evolutionary time from the whole genome perspective. In order to re-estimate the evolution time of angiosperms, an evolution rate correction model based on genomic data is established according to the idea that shared polyploidy events or shared divergence events should have the same Ks peak. The results were as follows:(1)Three common ways to obtain Ks distribution were compared and analyzed, which showed that the best way was to extract the median of Ks values on collinear blocks.(2)The change process of Ks distribution was simulated with time accumulation coefficient(v)of Ks values. When v was assumed to obey the normal distribution, the Ks distribution had a long tail phenomenon.(3)The correction process was described in detail, which was conducive to the understanding and wide spread of this method. From the application of correction method in angiosperms, it was found that the Ks peak before correction was not linear with time, while the Ks peak after correction was directly proportional to time, indicating that it is very necessary to estimate the time of species evolution events after correcting the Ks peak. It was also found that although the evolution rate of angiosperms was significantly different, the evolution rate between different branches was still partially consistent. For example, Magnoliids had the slowest evolutionary rate, followed by Eudicots and Monocots. When the environment changed greatly, most species of different lineages of angiosperms had synchronous radial evolution and adaptive evolution. Finally, a relatively reliable angiosperm evolution time axis was establish, which helps to understand the evolution process and model, especially to understand the phylogenetic relationship and the causes of diversity and provides phylogenetic and evolutionary support for plant research. [ABSTRACT FROM AUTHOR]