Christiane M. Ritz

AFLP markers as a tool to reconstruct complex relationships: A case study in Rosa (Rosaceae)

The genus Rosa has a complex evolutionary history caused by several factors, often in conjunction: extensive hybridization, recent radiation, incomplete lineage sorting, and multiple events of polyploidy. We examined the applicability of AFLP markers for reconstructing (species) relationships in Rosa, using UPGMA clustering, Wagner parsimony, and Bayesian inference. All trees were well resolved, but many of the deeper branches were weakly supported. The cluster analysis showed that the rose cultivars can be separated into a European and an Oriental cluster, each being related to different wild species. The phylogenetic analyses showed that (1) two of the four subgenera (Hulthemia and Platyrhodon) do not deserve subgeneric status; (2) section Carolinae should be merged with sect. Cinnamomeae; (3) subsection Rubigineae is a monophyletic group within sect. Caninae, making sect. Caninae paraphyletic; and (4) there is little support for the distinction of the five other subsections within sect. Caninae. Comparison of the trees with morphological classifications and with previous molecular studies showed that all methods yielded reliable trees. Bayesian inference proved to be a useful alternative to parsimony analysis of AFLP data. Because of their genome-wide sampling, AFLPs are the markers of choice to reconstruct (species) relationships in evolutionary complex groups.

Microsatellite Analyses of Artificial and Spontaneous Dogrose Hybrids Reveal the Hybridogenic Origin of Rosa micrantha by the Contribution of Unreduced Gametes

Dogroses are characterized by a unique meiosis system, the so-called canina meiosis, which facilitates sexual reproduction at odd-number ploidy. The mostly pentaploid somatic level of dogroses is restored by a merger of haploid sperm cells and tetraploid egg cells. We analyzed experimental hybrids between different dogrose species using microsatellites to determine pollen-transmitted alleles. This information was used to reconstruct the putative hybridogenic origin of Rosa micrantha and R. dumalis and to estimate the frequency of spontaneous hybridization in a natural population. We found no evidence for the hybrid origin of R. dumalis, but our data suggest that R. micrantha presumably arose by hybridization between R. rubiginosa and R. canina or R. corymbifera. We observed only hexaploid individuals of R. micrantha, thus the establishment of this hybridogenic species was favored when unreduced gametes contributed to their origin. We demonstrate that spontaneous hybrids originated infrequently from the parental species in a natural population, but hybridization was often associated with the formation of unreduced gametes. We postulate that unreduced gametes play a major role in the evolutionary success of dogrose hybrids because they provide highly homologous chromosomes crucial for bivalent formation during canina meiosis and thus ensuring this unique form of sexual reproduction.

Inheritance of growth form and mechanical characters in reciprocal polyploid hybrids of Rosa section Caninae- : implications for the ecological niche differentiation and radiation process of hybrid offspring

Within Rosa section Caninae (dogroses) two different growth types exist, arching (L-type) and erect (D-type). Due to the specific mode of chromosome allocation during meiosis, character inheritance in dogroses is maternally skewed. In this paper we try to assess the mode of inheritance of the ‘growth form’ in reciprocal hybrids of R. canina L. and R. rubiginosa L. to predict possible ecological niches and radiation processes of hybridogenic offspring. A quantitative analysis of mechanical properties indicates that neither an expected parentally skewed nor an intermediate habit was expressed by the hybrids, but a dominant L-type as in R. canina, regardless of the parental relationship (pollen-parent or seed-parent). Our results implicate two possible scenarios to be further tested: (a) R. canina acts as a species with a dominant allele for the growth form character. If so, this would be the first evidence of a Mendelian character inheritance in the dogroses. (b) ‘Growth form’ in the dogroses is not a Mendelian character, but a syndrom which realises as an emergent functional property with underlying phenotypic structural differences in stem and wood anatomy.

Different evolutionary histories of two Phragmidium species infecting the same dog rose hosts.

Rust fungi in the genus Phragmidium are frequent pathogens of both wild and cultivated roses. We investigated the occurrence and relationships of rusts on dog roses, Rosa sect. Caninae (Rosa canina, R. corymbifera and R. rubiginosa) in Germany. Two Phragmidium species, P. mucronatum and P. tuberculatum, were able to infect each of the three dog rose species examined. However, the overall infection of R. rubiginosa was significantly lower, which could be important for rose breeding. Despite overlapping host ranges, the evolutionary background of P. tuberculatum and P. mucronatum is quite distinct. Phylogenetic analyses of the D1/D2 region of the LSU rDNA suggest that P. mucronatum shares a common ancestor with other rose rusts, whereas P. tuberculatum evolved from a Rubus-Sanguisorba rust clade and must have undergone a host shift to Rosa spp.

Tracking the origin of invasive Rosa rubiginosa populations in Argentina.

The exact geographic origin of invasive species populations is rarely known; however, such knowledge is vital to understanding species’ invasion success, spread, and evolution as well as for assessing any biological control options. We investigated the shrub Rosa rubiginosa L., focusing on the presumed European origin of invasive populations in Argentina. We analyzed eight polymorphic microsatellite loci among 102 native (European) and 29 invasive (mainly central Argentinean and Patagonian) populations. Genetic diversity in the invasive range was clearly lower than in the native range, possibly because of a low number of introductions. Contrary to earlier hypotheses, the interpretation of principal coordinate analysis results and Jaccard dissimilarities contradicts the idea of the Argentinean populations having a Spanish origin. Instead, we found a close similarity between Argentinean samples and those from Germany, the Czech Republic, and Austria. We therefore assume that these neighboring countries are the most probable source regions for the Argentinean populations, which in some cases may also have arrived via Chile. According to historic information, emigrants from these regions may have introduced R. rubiginosa to South America in the nineteenth century on at least two occasions, either for food or as rootstock material for propagating living fences.

Epigenetic Patterns in Genetically Imbalanced Polyploid Dog Rose Hybrids (Rosa L. sect. Caninae (DC.) Ser.) Revealed by cDNA–Amplified Fragment Length Polymorphisms and Methylation-Sensitive Amplified Polymorphisms

Premise of research. Spontaneous hybrids between species of Rosa sect. Caninae represent a unique example to study the genetic and epigenetic consequences of an imbalanced parental contribution to polyploid hybrids. Due to the unique canina meiosis, pentaploid or hexaploid dog rose hybrids contain a single subgenome transmitted by the haploid pollen grain of the paternal species and four to five subgenomes transmitted by the tetraploid or pentaploid egg cell of the maternal species. During this study, we investigated epigenetic changes in spontaneous reciprocal hybrids between the subsections Caninae and Rubigineae compared to their parental species in a natural population in eastern Germany. Methodology. For investigating epigenetic patterns, we applied cDNA–amplified fragment length polymorphisms (AFLPs) and methylation-sensitive amplified polymorphisms (MSAPs). Additionally, we analyzed microsatellite data and measured morphological characters. Pivotal results. In line with expectations deduced from the genetic composition of the pentaploid and hexaploid hybrids, we observed a maternal bias of DNA methylation and expression patterns. We did not detect silencing of the respective paternal subgenomes. However, the percentage of paternally expressed fragments differed between plant organs. We found a higher number of paternally expressed fragments in sepals compared to leaves, suggesting that the parental genetic information underwent a rapid subfunctionalization in recently formed hybrids. Moreover, epigenetic data obtained from cDNA-AFLPs and MSAPs correlated stronger with morphology than with genetic data, based on microsatellites. Conclusions. The genetic contribution of subgenomes is strongly biased toward the maternal parent in dog rose hybrids, leading to a nearly apomictic mode of inheritance. However, we found that the underrepresented paternal genome is not silenced but transcribed and differentially expressed between plant organs. The correlation between epigenetic data and morphological data implies that the probably fast-evolving epigenetic changes have a major impact on dog rose phenotypes and may affect the establishment of hybrids in natural populations.