Rosa chinensis var. spontanea, an endemic and endangered plant of China, is one of the key ancestors of modern roses and a source for famous traditional Chinese medicines against female diseases, such as irregular menses and dysmenorrhea. In this study, the complete chloroplast (cp) genome of R. chinensis var. spontanea was sequenced, analyzed, and compared to congeneric species. The cp genome of R. chinensis var. spontanea is a typical quadripartite circular molecule of 156,590 bp in length, including one large single copy (LSC) region of 85,910 bp and one small single copy (SSC) region of 18,762 bp, separated by two inverted repeat (IR) regions of 25,959 bp. The GC content of the whole genome is 37.2%, while that of LSC, SSC, and IR is 42.8%, 35.2% and 31.2%, respectively. The genome encodes 129 genes, including 84 protein-coding genes (PCGs), 37 transfer RNA (tRNA) genes, and eight ribosomal RNA (rRNA) genes. Seventeen genes in the IR regions were found to be duplicated. Thirty-three forward and five inverted repeats were detected in the cp genome of R. chinensis var. spontanea. The genome is rich in SSRs. In total, 85 SSRs were detected. A genome comparison revealed that IR contraction might be the reason for the relatively smaller cp genome size of R. chinensis var. spontanea compared to other congeneric species. Sequence analysis revealed that the LSC and SSC regions were more divergent than the IR regions within the genus Rosa and that a higher divergence occurred in non-coding regions than in coding regions. A phylogenetic analysis showed that the sampled species of the genus Rosa formed a monophyletic clade and that R. chinensis var. spontanea shared a more recent ancestor with R. lichiangensis of the section Synstylae than with R. odorata var. gigantea of the section Chinenses. This information will be useful for the conservation genetics of R. chinensis var. spontanea and for the phylogenetic study of the genus Rosa, and it might also facilitate the genetics and breeding of modern roses.

Roses are important woody plants featuring a set of important traits that cannot be investigated in traditional model plants. Here, we used the restriction-site associated DNA sequencing (RAD-seq) technology to develop a high-density linkage map of the backcross progeny (BC1F1) between Rosa chinensis ‘Old Blush’ (OB) and R. wichuraiana ‘Basyes’ Thornless’ (BT). We obtained 643.63 million pair-end reads and identified 139,834 polymorphic tags that were distributed uniformly in the rose genome. 2,213 reliable markers were assigned to seven linkage groups (LGs). The length of the genetic map was 1,027.425 cM in total with a mean distance of 0.96 cM per marker locus. This new linkage map allowed anchoring an extra of 1.21/23.14 Mb (12.18/44.52%) of the unassembled OB scaffolds to the seven reference pseudo-chromosomes, thus significantly improved the quality of assembly of OB reference genome. We demonstrate that, while this new linkage map shares high collinearity level with strawberry genome, it also features two chromosomal rearrangements, indicating its usefulness as a resource for understanding the evolutionary scenario among Rosaceae genomes. Together with the newly released genome sequences for OB, this linkage map will facilitate the identification of genetic components underpinning key agricultural and biological traits, hence should greatly advance the studies and breeding efforts of rose.

Genus Rosa (Rosaceae) has a base chromosome number of x = 7. Ploidy levels of wild species range from 2n = 2x = 14 to 2n = 8x = 56. In this paper, one decaploid, the highest naturally occurring ploidy never reported before in the genus was detected in the karyological study of an endemic wild species, R. praelucens Byhouwer to Zhongdian Plateau, Yunnan, China. Its karyotype formula was 2n = 10x = 70 = 2st + 6sm + 62m and the karyotype was 2B. Chromosome No. 6 was subterminal. Chromosome No. 15, No. 22 and No. 23 were submedian. According to its karyomorphology, R. praelucens derived not from auto polyploidization directly but from inter-specifi c hybridization. Polyploidization and inter-species hybridization both might have played important roles in the origin of R. praelucens associated with effect of high altitude environment. Further research on this species is warranted to provide helpful evidences to understand the differentiation and evolution of the Genus Rosa, and even clues to trace the process of speciation in Sino-Himalayan region.

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Powdery mildew is a major disease of economic importance in cut and pot roses. As an alternative to conventional resistance breeding strategies utilizing single-dominant genes or QTLs, mildew resistance locus o (MLO)-based resistance might offer some advantages. In dicots such as Arabidopsis, pea, and tomato, loss-of-function mutations in MLO genes confer high levels of broad-spectrum resistance. Here, we report the isolation and characterization of four MLO homologs from a large rose EST collection isolated from leaves. These genes are phylogenetically closely related to other dicot MLO genes that are involved in plant powdery mildew interactions. Therefore, they are candidates for MLO genes involved in rose powdery mildew interactions. Two of the four isolated genes contain all of the sequence signatures considered to be diagnostic for MLO genes. We mapped all four genes to three linkage groups and conducted the first analysis of alternative alleles. This information is discussed in regards to a reverse genetics approach aimed at the selection of rose plants that are homozygous for loss-of-function in one or more MLO genes.