Speciation by triparental hybridization in genus Sorbus (Rosaceae).

Hybridization associated with polyploidization and apomixis is a frequent mechanism of speciation. Sorbus is a genus with ongoing hybridization resulting in a polyploid complex with different parental lineage. Triparens is the smallest hybridogenous subgenus of Sorbus so far known to comprise only two taxa, S. intermedia and S. × liljeforsii that combine the genomes of three taxa (S. aria agg., S. aucuparia and S. torminalis). To elucidate the origins of S. dacica, S. paxiana and S. tauricola, three new trigenomic candidates formerly believed to be of biparental origin with either S. aria agg. × S. aucuparia or S. aria agg. × S. torminalis lineage we combined data from HPLC and chloroplast DNA analysing additional 33 related taxa as well. We concluded that the 'torminalis-type' flavonoid profile and the 'aucuparia-type' plastid indicate the participation of both S. torminalis and S. aucuparia resulting in the formation of S. dacica, S. paxiana and S. tauricola. Sorbus aria agg. as the third ancestor and as a necessary link to meet genes of S. torminalis and S. aucuparia in one genome is obvious from morphological features (densely tomentose undersides of leaves). The tetraploid cytotypes and obligate pseudogamy of S. dacica and S. paxiana were determined by flow cytometry and are published here for the first time. The most probable evolutionary scenario for Triparens species is: 1. a diploid sexual S. aucuparia as pollen acceptor hybridized with a tetraploid apomictic taxon from the S. aria agg. producing a triploid apomictic taxon with 'aucuparia-type' plastid inherited maternally; 2. during a second crossing event this subgenus Soraria hybrid as maternal progenitor hybridized with the sexual diploid S. torminalis (providing gene(s) of apigenin O-glucuronide synthesis) forming a tetraploid Triparens hybrid with 'aucuparia-type' plastid and 'torminalis-type' flavonoids.

Molecular phylogenetics and historical biogeography of Sorbus sensu stricto (Rosaceae).

Explaining how plants from eastern Asia migrated to other Northern Hemisphere regions is still challenging. The genus Sorbus sensu stricto (including c. 88 species) is considered as a good example to illuminate this scenario, due to the wide distribution in the temperate zone and high diversity in the Himalayas and Hengduan Mountains. Based on four nuclear markers (LEAFY-2, GBSSI-1, SBEI and WD) and one chloroplast marker (rps16-trnK), we reconstructed the phylogenetic relationship of Sorbus using 54 taxa (60% of the genus representing all subgenera, sections, or series and geographical areas in the previous classifications), and estimated divergence time and historical biogeography of the genus. Phylogenetic analyses supported that the subgenera Sorbus and Albo-carmesinae, as defined by traditional morphological characters (such as fruit color), are suitable. However, five clades defined by phylogenetic analysis of the genus are not consistent with traditionally defined sections or series. Molecular dating and biogeographic reconstruction showed that the age of the most recent common ancestor was estimated at 41mya (95% HPD: 49-35mya) in eastern Asia. Four dispersal events are assumed to explain the wide distribution of Sorbus in the temperate zone and diversification in the edges of Qinghai-Tibet Plateau (QTP). Species dispersed from eastern Asia to the Tianshan Mountains, North America and Europe during the Oligocene and Miocene period. We found that polyploidization occurred multiple times in the subgenus Albo-carmesinae, in the Tianshan Mountains, Himalayas, and H-D Mountains. Finally, we suggest that apomixis, polyploidization, and hybridization may have combined with the multistage uplifting of Himalayas and H-D Mountains (and the subsequent increases in geologic, ecological and climatic heterogeneity) to drive the striking species diversity of Sorbus in this region.

Isozyme polymorphism and genetic structure of the population of Sorbus torminalis (L.) Crantz from the Bytyn Forest (Poland).

Dormant buds collected from 35 wild service trees (Sorbus torminalis) in the Bytyn Forest were tested with horizontal gel electrophoresis to assess the genetic structure of the population. Among 16 investigated isozyme loci, seven loci (ADH-A, 6PGD-A, GDH-B, ME-A, SOD-A, PGM-A, PGM-B) proved to be polymorphic, whereas the other nine loci (SDH-A, SDH-B, DIA-C, DIA-D, FLE-A, FLE-B, GOT-B, IDH-A, IDH-B) were monomorphic. The number of alleles per polymorphic locus ranged from two to three, with a mean of 2.29. The average observed and expected heterozygosities were 0.2665 and 0.3462, respectively. The combined FIS value over all polymorphic loci was 0.2179, which reflects a substantial deficit of heterozygotes. Two polymorphic loci (SOD-A, PGM-A) were identified in S. torminalis for the first time.