Qigang Wang

Decaploidy in Rosa praelucens Byhouwer (Rosaceae) Endemic to Zhongdian Plateau, Yunnan, China

Abstract 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-specific 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.

The Complete Chloroplast Genome of a Key Ancestor of Modern Roses, Rosa chinensis var. spontanea, and a Comparison with Congeneric Species

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.

Antisense RhMLO1 Gene Transformation Enhances Resistance to the Powdery Mildew Pathogen in Rosa multiflora

AbstractPowdery mildew is one of the most important crop diseases worldwide. Genetic analysis has revealed that mutant alleles of the Mlo gene cause broad-spectrum resistance against pathogens found in cereal. In this study, the possibility of inducing powdery mildew (Podosphaera pannosa) resistance via transgenic technology in the rose was examined. The transgenic lines were confirmed for integration and copy number of the transgenes based on PCR and Southern blots. A clear correlation was found between resistance and the accumulation of silenced RhMLO1, based on real-time fluorescent quantitative PCR and resistance analysis. Compared with the control plants, transgenic roses displayed higher resistance levels. Furthermore, the results indicated that RhMLO1 has a negative role in the rose–powdery mildew pathogen interaction. This demonstrates the potentially viable strategy of rendering the Mlo homologs partially non-functional via a transgenic approach or mutagenesis in order to counter powdery mildew in Rosa. To the best of our knowledge, this study is one of the first attempts at using a Mlo-based resistance strategy to combat powdery mildew in Rosa.

Yalongjiang River Has Had an Important Role in the Dispersal and Divergence of Rosa soulieana in the Hengduan Mountains of China.

The Hengduan Mountains are the core of the Sino-Himalayan Floristic Region. Rosa soulieana Crép. is an important wild rose species that is widely distributed in the Hengduan Mountains. To provide better future utilization of this wild rose, and also to add some possible proof of the effect of geomorphological and ecological characteristics of the Hengduan Mountains on the current spatial distribution and genetic diversity of local species, the genetic diversity and genetic structure of 556 individuals from 37 populations of R. soulieana were studied using fluorescent amplified fragment length polymorphisms (AFLPs). R. soulieana showed a moderately high level of genetic diversity and a high level of genetic differentiation at the species level. The total percentage of polymorphic loci, total heterozygosity (Ht), Shannon index (I), and heterozygosity value within populations (Hs) were 97.8%, 0.253, 0.339, and 0.139, respectively. More than half of the total genetic variation (54.0%) occurred within populations, and the overall gene differentiation coefficient (Gst) was 0.451. The genetic differentiation among populations was positively and significantly correlated with geographic distance. The neighbor-joining cluster and the Bayesian analysis divided all the populations and individuals into 3 groups, and did not support the morphology based intraspecific varieties. The results confirmed that the ancient R. soulieana of the third group survived in northwestern Yunnan and Yalongjiang valley and then moved upnorth along the valley. The spatial distribution of the other two groups was the result of allopatric divergence due to long period of adaptation to the different climatic conditions of its distribution at either side of the Yalongjiang River.

High genetic diversity and differentiation of an extremely narrowly distributed and critically endangered decaploid rose ( Rosa praelucens ): implications for its conservation

Rosa praelucens is a critically endangered decaploid alpine rose with an extremely narrow geographic distribution in Northwestern Yunnan, China. We sampled almost all the extant individuals (527 individuals in 31 natural locations and 56 individuals preserved in three local living collections) to assess the genetic variation and to probe the genetic connectivity among the individuals and populations based on three cpDNA intergenic spacers and six fluorescent amplified fragment length polymorphism (AFLP) markers. The morphological traits from seven populations were also measured. R. praelucens exhibited high levels of morphological variation, genetic diversity, and differentiation. The extant individuals were clustered into eight groups in neighbor-net networks, and subsequent Bayesian analysis assigned them into three larger gene pools, both in accordance with their morphological traits, especially flower color. The living collections embraced two private cpDNA haplotypes and included three out of the species’ total eight AFLP genotypes. Rhizome clonal growth, decaploid, and mixed breeding system may largely contribute to high genetic diversity and differentiation in R. praelucens. We concluded that the endangered status of R. praelucens may mainly be due to habitat fragmentation and loss and inherent reproductive difficulties, rather than low genetic diversity. The populations contributing higher cpDNA genetic diversity, representing more AFLP genotypes, and encompassing private cpDNA haplotypes should be given conservation priority by creating plant-micro reserves. The living collections should also be targeted for further ex situ conservation, population recovery, and reintroduction of R. praelucens plants.

Nuclear DNA content and 1Cx-value variations in genus Rosa L.

In order to investigate the systematic relationship and to complete the karyological data of rose, for the purpose of exploring desirable traits for genetic improvement of modern cultivars, nuclear DNA content of 204 accessions representing almost all sections of genus Rosa were estimated by flow cytometry. The 1Cx-value of each taxon was calculated according to the estimated DNA content. The results were as follows: (1) nuclear DNA content of the studied taxa varied from 0.73 pg in diploid R. zhongdianensis (Section Pimpinellifoliae) to 5.07 pg in decaploid R. praelucens (Section Microphyllae), and nuclear DNA content of rose species generally increased with, but not simply proportional to, ploidy level; (2) 1Cx-value varied from 0.37 pg in R. zhongdianensis to 0.89 pg in R. brunonii (Section Synstylae), and the studied taxa were significantly different from each other in 1Cx-value; (3) there exist significant differences of 1Cx-values among sections, varying from 0.46 pg in Section Pimpinellifoliae to 0.77 pg in Section Synstylae; (4) ploidy level varied within most sections except in Section Banksianae, Section Bracteatae, Section Laevigatae and Section Synstylae, while the variation of 1Cx-value with ploidy level differed greatly among sections. The results suggested that taxonomic section should be taken into consideration when assigning ploidy of rose species from rapid estimates of DNA content by flow cytometry. Also, although it does not reflect the taxonomy and biosystematics sufficiently, nuclear DNA content and 1Cx-value can be used as reference points in the biogeographic, systematic and evolutionary study of genus Rosa.

Cloning and Analysis of NBS-LRR Type Disease Resistance Gene Analogs from Rosa rubus in Yunnan

In the study of NBS resistance genes of Yunnan wild Rosa, the degenerate oligonucleotide primers were designed according to the conserved motifs NBS-LRR of most plant resistance (R) genes. The cDNA fragments were isolated from Rosa rubus by reverse transcription PCR (RT-PCR). Then four resistance gene analogs (RGAs) were sequenced and named as AC9, AC39, AC50 and AC68, which contain NBS-LRR domain. The sequence of each RGAs was compared with NBS region of eleven resistance genes reported before, and the similarities of amino-acid sequences ranged from 5.4% to 79.2%, and these four RGAs were clustered a group with Mi、RPS2、Pib and RPM1 gene. These results showed that the four RGAs will be used as molecular markers for screening candidate disease resistance genes and genetic map construction of Rosa rubus in the future.