Microsporogenesis and meiotic behavior in nine species of the genus Pinus

The meiotic behavior of 10 taxa （nine species and one variety） of the genus Pinus was investigated using pollen mother cells （PMCs） to reveal the differentiation among karyotypes. Chromosome spreads were prepared by conventional squashing. The meiotic index and the average configuration were higher, whereas the frequency of aberrance （chromosomal bridges, fragments, or micronuclei） was lower, in all 10 taxa compared with other gynmosperms. The meiotic index, average configuration, and frequency of irregularity were found to be uniform among the species. It was shown that the genomes of the Pinus species investigated were highly stable, confirming results of previous mitotic analyses in this genus. However, slight differentiation of homologous chromosomes among genomes was revealed by analysis of meiotic configurations in Pinus nigra var. poiretiana. Quadrivalents were observed in 9.31% of PMCs in this species. This is the first time that quadrivalents have been observed in gymnosperms.

Phylogenomic conflict analyses in the apple genus Malus s.l.reveal widespread hybridization and allopolyploidy driving diversification,with insights into the complex biogeographic history in the Northern Hemisphere

Phylogenomic evidence from an increasing number of studies has demonstrated that different data sets and analytical approaches often reconstruct strongly supported but conflicting relationships.In this study,785 single-copy nuclear genes and 75 complete plastomes were used to infer the phylogenetic relationships and estimate the historical biogeography of the apple genus Malus sensu lato,an economically important lineage disjunctly distributed in the Northern Hemisphere and involved in known and suspected hybridization and allopolyploidy events.The nuclear phylogeny recovered the monophyly of Malus s.l.(including Docynia);however,the genus was supported to be biphyletic in the plastid phylogeny.An ancient chloroplast capture event in the Eocene in western North America best explains the cytonuclear discordance.Our conflict analysis demonstrated that ILS,hybridization,and allopolyploidy could explain the widespread nuclear gene tree discordance.One deep hybridization event(Malus doumeri)and one recent event(Malus coronaria)were detected in Malus s.l.Furthermore,our historical biogeographic analysis integrating living and fossil data supported a widespread East Asianwestern North American origin of Malus s.l.in the Eocene,followed by several extinction and dispersal events in the Northern Hemisphere.We also propose a general workflow for assessing phylogenomic discordance and biogeographic analysis using deep genome skimming data sets.

Behavior of Meiotic Chromosomes in Pinus wallichiana,P.strobus and Their Hybrid and nrDNA Localization in Pollen Mother Cells of the Hybrid by Using FISH

The complete process of meiosis was investigated in Pinus wallichiana, P. strobus and their artificial hybrid （F1） using microsporocytes. It is revealed that there were slightly lower chiasma frequency, lower ring bivalent frequency, lower meiotic index and distinctly higher frequency of aberrance （chromosomal bridges, fragments or micronuclei） in pollen mother cells （PMCs） of the hybrid （F1） than those of the parental species, which showed a certain degree of differentiation between homologous chromosomes of the two parents. However, relatively higher frequency of ring bivalents and higher meiotic index in all the three entities indicate the great stability of genomes of parental species, and the differentiation of genomes between the two parents must have been slight. Total nineteen signal loci of 18S rDNA were observed in nine bivalents of the hybrid （F1）, among which one bivalent bears two loci, while the others have only one. It is suggested that distinct differentiation at genetic level existed in homologous chromosomes of the two parental species, whereas only slight differentiation at karyotypic and genomic levels take place between the parent species.

Evolution of the platycodonoid group with particular references to biogeography and character evolution

The Qinghai‐Tibet Plateau（QTP）is an important center of origin and diversification for many northern temperate plants.The hypothesis＂out‐of‐QTP＂suggests that the majority of northern temperate plants have originated and dispersed from the QTP and adjacent regions.An interesting question is whether the biogeographic history of the platycodonoids（Campanulaceae）,a group mainly distributed in the QTP and adjacent regions,coincides with the hypothesis＂out‐of‐QTP＂？Furthermore,how have the diagnostic characters of the platycodonoids evolved？In the present study,all 10genera of the platycodonoids were sampled for molecular phylogeny and dating analyses,and ancestral states of distribution and characters were reconstructed.The results do not support the platycodonoids as an＂out‐of‐QTP＂group,but instead they might have descended from Tethyan ancestors.The dispersal and diversification of the platycodonoids in Asia might have been driven by the uplift of the QTP.The present study highlights the importance of the Tethyan Tertiary flora for the origin of the Sino‐Himalayan flora and the influence of the uplift of QTP on diversification of northern temperate plants.In addition,character state reconstruction reveals that the inferior ovary,capsule,long‐colpate pollen,and chromosome number 2n=14 are probably ancestral states.

A special issue to mark the 90th Anniversary ofCollege of Life Sciences, Zhejiang University

The College of Life Sciences (CLS) remains one of the most prestigious—and the oldest—colleges in Zhejiang University. This special issue, which includes 16 reviews contributed by our alumni and faculties, is dedicated to mark the 90th Anniversary of CLS.