Abstract
The genus Sedum, with about 470 recognized species, is classified in the family Crassulaceae of the order Saxifragales. Phylogenetic relationships within the Saxifragales are still unresolved and controversial. In this study, the plastome of S. plumbizincicola was firstly presented, with a focus on the structural analysis of rrn operon and phylogenetic implications within the order Saxifragaceae. The assembled complete plastome of S. plumbizincicola is 149,397 bp in size, with a typical circular, double-stranded, and quadripartite structure of angiosperms. It contains 133 genes, including 85 protein-coding genes (PCGs), 36 tRNA genes, 8 rRNA genes, and four pseudogenes (one ycf1, one rps19, and two ycf15). The predicted secondary structure of S. plumbizincicola 16S rRNA includes three main domains organized in 74 helices. Further, our results confirm that 4.5S rRNA of higher plants is associated with fragmentation of 23S rRNA progenitor. Notably, we also found the sequence of putative rrn5 promoter has some evolutionary implications within the order Saxifragales. Moreover, our phylogenetic analyses suggested that S. plumbizincicola had a closer relationship with S. sarmentosum than S. oryzifolium, and supported the taxonomic revision of Phedimus. Our findings of the present study will be useful for further investigation of the evolution of plastid rRNA operon and phylogenetic relationships within Saxifragales.
Highlights
The genus Sedum comprises more than 420 recognized species, which is the most species-rich member of the family Crassulaceae [1,2]
We found that S. plumbizincicola had a closer relationship with S. sarmentosum
We focused on the analyses of the primary and secondary structures of plastid rRNA genes
Summary
The genus Sedum comprises more than 420 recognized species, which is the most species-rich member of the family Crassulaceae [1,2]. The family Crassulaceae, together with 14 other family members, has been classified in the order Saxifragales. Plants 2019, 8, 386 efforts have been focused on the evolution of Saxifragales, phylogenetic relationships within the order are still unresolved due apparently to a rapid, ancient radiation [7,8,9,10,11,12]. The plastid genome (plastome) is a circular biological macromolecule with a typical quadripartite structure [13,14,15]. In higher plants, compared with hundreds or thousands of tandem repeats in nuclear ribosomal RNA genes [16,17,18], typical plastid rRNA genes are characterized by a pair of inverted rrn operons, which show the gene order of rrn, rrn, rrn4.5, and rrn5 [19]. The plastomes have been widely accepted as a popular tool for phylogenetic studies [7,20,21,22,23,24,25,26]
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