The complete chloroplast genome sequence of watercress (Nasturtium officinale R. Br.): Genome organization, adaptive evolution and phylogenetic relationships in Cardamineae.

Watercress (Nasturtium officinale R. Br.), an aquatic leafy vegetable of the Brassicaceae family, is known as a nutritional powerhouse. Here, we de novo sequenced and assembled the complete chloroplast (cp) genome of watercress based on combined PacBio and Illumina data. The cp genome is 155,106 bp in length, exhibiting a typical quadripartite structure including a pair of inverted repeats (IRA and IRB) of 26,505 bp separated by a large single copy (LSC) region of 84,265 bp and a small single copy (SSC) region of 17,831 bp. The genome contained 113 unique genes, including 79 protein-coding genes, 30 tRNAs and 4 rRNAs, with 20 duplicate in the IRs. Compared with the prior cp genome of watercress deposited in GenBank, 21 single nucleotide polymorphisms (SNPs) and 27 indels were identified, mainly located in noncoding sequences. A total of 49 repeat structures and 71 simple sequence repeats (SSRs) were detected. Codon usage showed a bias for A/T-ending codons in the cp genome of watercress. Moreover, 45 RNA editing sites were predicted in 16 genes, all for C-to-U transitions. A comparative plastome study with Cardamineae species revealed a conserved gene order and high similarity of protein-coding sequences. Analysis of the Ka/Ks ratios of Cardamineae suggested positive selection exerted on the ycf2 gene in watercress, which might reflect specific adaptations of watercress to its particular living environment. Phylogenetic analyses based on complete cp genomes and common protein-coding genes from 56 species showed that the genus Nasturtium was a sister to Cardamine in the Cardamineae tribe. Our study provides valuable resources for future evolution, population genetics and molecular biology studies of watercress.

Yan C ，Du J ，Gao L ，Li Y ，Hou X ... -  《-》

The complete chloroplast genome sequence of yellow mustard (Sinapis alba L.) and its phylogenetic relationship to other Brassicaceae species.

As a member of the large Brassicaceae family, yellow mustard (Sinapis alba L.) has been used as an important gene pool for the genetic improvement of cash crops in Brassicaceae. Understanding the phylogenetic relationship between Sinapis alba (S. alba) and other Brassicaceae crops can provide guidance on the introgression of its favorable alleles into related species. The chloroplast (cp) genome is an ideal model for assessing genome evolution and the phylogenetic relationships of complex angiosperm families. Herein, we de novo assembled the complete cp genome of S. alba by integrating the PacBio and Illumina sequencing platforms. A 153,760 bp quadripartite cycle without any gap was obtained, including a pair of inverted repeats (IRa and IRb) of 26,221 bp, separated by a large single copy (LSC) region of 83,506 bp and a small single copy (SSC) region of 17,821 bp. A total of 78 protein-coding genes, 30 tRNA genes, and four rRNA genes were identified in this cp genome, as were 89 simple sequence repeat (SSR) loci of 18 types. The codon usage analysis revealed a preferential use of the Leu codon with the A/U ending. The phylogenetic analysis using 82 Brassicaceae species demonstrated that S. alba had a close relationship with important Brassica and Raphanus species; moreover, it likely originated from a separate evolutionary pathway compared with the congeneric Sinapis arvensis. The synonymous (Ks) and non-synonymous (Ks) substitution rate analysis showed that genes encoding "Subunits of cytochrome b/f complex" were under the lowest purifying selection pressure, whereas those associated with "Maturase", "Subunit of acetyl-CoA", and "Subunits of NADH-dehydrogenase" underwent relatively higher purifying selection pressures. Our results provide valuable information for fully utilizing the S. alba cp genome as a potential genetic resource for the genetic improvement of Brassica and Raphanus species.

Du X ，Zeng T ，Feng Q ，Hu L ，Luo X ，Weng Q ，He J ，Zhu B ... -  《-》

Characterization of the complete chloroplast genome of Brassica oleracea var. italica and phylogenetic relationships in Brassicaceae.

Broccoli (Brassica oleracea var. italica) is an important B. oleracea cultivar, with high economic and agronomic value. However, comparative genome analyses are still needed to clarify variation among cultivars and phylogenetic relationships within the family Brassicaceae. Herein, the complete chloroplast (cp) genome of broccoli was generated by Illumina sequencing platform to provide basic information for genetic studies and to establish phylogenetic relationships within Brassicaceae. The whole genome was 153,364 bp, including two inverted repeat (IR) regions of 26,197 bp each, separated by a small single copy (SSC) region of 17,834 bp and a large single copy (LSC) region of 83,136 bp. The total GC content of the entire chloroplast genome accounts for 36%, while the GC content in each region of SSC,LSC, and IR accounts for 29.1%, 34.15% and 42.35%, respectively. The genome harbored 133 genes, including 88 protein-coding genes, 37 tRNAs, and 8 rRNAs, with 17 duplicates in IRs. The most abundant amino acid was leucine and the least abundant was cysteine. Codon usage analyses revealed a bias for A/T-ending codons. A total of 35 repeat sequences and 92 simple sequence repeats were detected, and the SC-IR boundary regions were variable between the seven cp genomes. A phylogenetic analysis suggested that broccoli is closely related to Brassica oleracea var. italica MH388764.1, Brassica oleracea var. italica MH388765.1, and Brassica oleracea NC_0441167.1. Our results are expected to be useful for further species identification, population genetics analyses, and biological research on broccoli.

Zhang Z ，Tao M ，Shan X ，Pan Y ，Sun C ，Song L ，Pei X ，Jing Z ，Dai Z ... -  《PLoS One》

Complete Chloroplast Genome Sequences of Kaempferia Galanga and Kaempferia Elegans: Molecular Structures and Comparative Analysis.

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Li DM ，Zhao CY ，Liu XF 《MOLECULES》

Complete chloroplast genome sequence of Fagopyrum dibotrys: genome features, comparative analysis and phylogenetic relationships.

Wang X ，Zhou T ，Bai G ，Zhao Y ... -  《Scientific Reports》