Drivers of diversification in Linum (Linaceae) by means of chromosome evolution: correlations with biogeography, breeding system and habit

BACKGROUND AND AIMS

Chromosome evolution leads to hybrid dysfunction and recombination patterns and has thus been proposed as a major driver of diversification in all branches of the tree of life, including flowering plants. In this study we used the genus Linum (flax species) to evaluate the effects of chromosomal evolution on diversification rates and on traits that are important for sexual reproduction. Linum is a useful study group because it has considerable reproductive polymorphism (heterostyly) and chromosomal variation (n = 6-36) and a complex pattern of biogeographical distribution.

METHODS

We tested several traditional hypotheses of chromosomal evolution. We analysed changes in chromosome number across the phylogenetic tree (ChromEvol model) in combination with diversification rates (ChromoSSE model), biogeographical distribution, heterostyly and habit (ChromePlus model).

KEY RESULTS

Chromosome number evolved across the Linum phylogeny from an estimated ancestral chromosome number of n = 9. While there were few apparent incidences of cladogenesis through chromosome evolution, we inferred up to five chromosomal speciation events. Chromosome evolution was not related to heterostyly but did show significant relationships with habit and geographical range. Polyploidy was negatively correlated with perennial habit, as expected from the relative commonness of perennial woodiness and absence of perennial clonality in the genus. The colonization of new areas was linked to genome rearrangements (polyploidy and dysploidy), which could be associated with speciation events during the colonization process.

CONCLUSIONS

Chromosome evolution is a key trait in some clades of the Linum phylogeny. Chromosome evolution directly impacts speciation and indirectly influences biogeographical processes and important plant traits.

Incomplete partitioning of pollinators by Linum suffruticosum and its co-flowering congeners

PREMISE OF THE STUDY

Linum suffruticosum shows variation in pollinator fit, pollen pick up, and local pollinators that predict pollen deposition rates. The species often co-flowers with other Linum species using the same pollinators. We investigated whether L. suffruticosum trait variation could be explained by local patterns of pollinator sharing and associated evolution to reduce interspecific pollen transfer.

METHODS

Pollinator observations were made in different localities (single species, co-flowering with other congeners). Floral traits were measured to detect differences across populations and from co-flowering species. Reproductive costs were quantified using interspecific hand-pollinations and measures of pollen-tube formation, combined with observations of pollen arrival on stigmas and pollen tube-formation under natural pollination in allopatric and sympatric localities.

KEY RESULTS

The size and identity of the most important pollinator of L. suffruticosum, and whether there was pollinator sharing with co-flowering species, appeared to explain floral trait variation related to pollinator fit. The morphological overlap of the flowers of L. suffruticosum with those of co-flowering species varied, depending on co-flowering species identity. A post-pollination incompatibility system maintains reproductive isolation, but conspecific pollen-tube formation was lower after heterospecific pollination. Under natural pollination at sites of co-flowering with congeners, conspecific pollen-tube formation was lower than at single-species localities.

CONCLUSIONS

Trait variation in L. suffruticosum appears to respond to the most important local pollinator. Locally, incomplete pollinator partitioning might cause interspecific pollination, imposing reproductive costs. This may generate selection on floral traits for reduced morphological overlap with co-flowering congeners, leading to the evolution of pollination ecotypes. This article is protected by copyright. All rights reserved.

Microsatellite marker development in the crop wild relative Linum bienne using genome skimming

PREMISE

Nuclear microsatellite markers were developed for Linum bienne, the sister species of the crop L. usitatissimum, to provide molecular genetic tools for the investigation of L. bienne genetic diversity and structure.

METHODS AND RESULTS

Fifty microsatellite loci were identified in L. bienne by means of genome skimming, and 44 loci successfully amplified. Of these, 16 loci evenly spread across the L. usitatissimum reference nuclear genome were used for genotyping six L. bienne populations. Excluding one monomorphic locus, the number of alleles per locus ranged from two to 12. Four out of six populations harbored private alleles. The levels of expected and observed heterozygosity were 0.076 to 0.667 and 0.000 to 1.000, respectively. All 16 loci successfully cross-amplified in L. usitatissimum.

CONCLUSIONS

The 16 microsatellite loci developed here can be used for population genetic studies in L. bienne, and 28 additional loci that successfully amplified are available for further testing.

Three new compounds with nitric oxide inhibitory activity from Tirpitzia sinensis, an ethnomedicinal plant from Southwest China

The medicinal plant Tirpitzia sinensis has been used by the Zhuang ethnic people in mountainous areas of Southwest China to stop bleeding, invigorate blood circulation, and treat inflammation and wounds. In order to further explore its traditional medicinal uses, the phytochemical constituents of this species were examined. Three new compounds, the lignan tirpitzin (1), the flavonoid tirpitzoside (2), and the furan-glycoside tirpitziol (3), along with five known compounds were isolated from the aerial part of T. sinensis for the first time. The structures of these compounds were elucidated by 1D and 2D NMR, LC/MS, IR spectrometric methods and compared with published data. The results of an in silico pharmacophore-based analysis showed potential targets of the new compounds, including ERBB2, IRAK4, LCK, JAK2, MAPK14, and MMP-12. These targets suggested that 1-3 may be involved with wound-healing and/or inflammation, leading to an in vitro assay of nitric oxide (NO) inhibition assays with lipopolysaccharide-induced BV-2 cells. All three new compounds displayed moderate NO inhibitory activity with the IC₅₀ values of 14.97 ± 0.87, 26.63 ± 1.32, and 17.09 ± 2.3 μM, respectively.

Lignans and diterpenes isolated from Tirpitzia ovoidea and their biological activities

A new lignan, tirpitzin A (17) together with 20 known compounds (1-16, and 18-21) were isolated from the ethyl acetate soluble fraction of ethanol extract of the aerial parts of Tirpitzia ovoidea. The structure of new compound was elucidated by means of spectroscopic analysis. Of the known compounds, 7-21 were isolated from Linaceae family for the first time. The pharmacological activity of the crude extracts was tested using a mouse inflammation model induced by dimethyl benzene. The results demonstrated that the ethyl acetate soluble fraction had anti-inflammatory activity. Moreover, the cytotoxic and anti-inflammatory activities of some compounds were studied. The new compound 17 showed moderate cytotoxic effect against BxPC-3 cell line (IC₅₀ = 19.51μmol·L^-1) and Compound 10 showed significant cytotoxicity against HepG2, HL-60, U87 and BxPC-3 cell lines with IC₅₀ values in the range 4.2-8.3μmol·L^-1. Additionally, Compounds 2, 10, 11, and 13 exhibited potent inhibitory effects on LPS-induced nitric oxide production in RAW 264.7 macrophages at the concentration of 50μmol·L^-1.

Pleistocene radiation of the serpentine-adapted genus Hesperolinon and other divergence times in Linaceae (Malpighiales)

PREMISE OF THE STUDY

Hesperolinon (western flax; Linaceae) is endemic to the western United States, where it is notable for its high and geographically concentrated species diversity on serpentine-derived soils and for its use as a model system in disease ecology. We used a phylogenetic framework to test a long-standing hypothesis that Hesperolinon is a neoendemic radiation.

METHODS

Five plastid and two ribosomal nuclear DNA gene regions were sampled from 105 populations of Hesperolinon, including all 13 recently recognized species across their known ranges. We used these data to generate population-level phylogenies of Hesperolinon. We also generated a robustly sampled chronogram of Linaceae using an eight-gene, 100-taxon supermatrix calibrated using fossil Linum pollen and a published chronogram of Malpighiales.

KEY RESULTS

Most diversification in Hesperolinon has taken place in the past 1-2 million yr, much more recently than previous estimates. Only the earliest-diverging species, H. drymarioides, was resolved as a clade. Denser taxon and gene sampling generally support previously proposed relationships within Linaceae, but with more recent diversification of key clades.

CONCLUSIONS

Hesperolinon is an excellent example of edaphic neoendemism, in support of Raven and Axelrod's hypothesis for the genus. Dense population-level sampling reveals a complex of incipient species, with clades poorly aligned with traditional morphological circumscriptions, likely due in part to continued gene flow. The diversification of Linaceae is more recent than previously estimated, and other recent radiations (e.g., Hugonia) warrant further study.

Isolation and structure elucidation of linolipins C and D, complex oxylipins from flax leaves

Two complex oxylipins (linolipins C and D) were isolated from the leaves of flax plants inoculated with phytopathogenic bacteria Pectobacterium atrosepticum. Their structures were elucidated based on UV, MS and NMR spectroscopic data. Both oxylipins were identified as digalactosyldiacylglycerol (DGDG) molecular species. Linolipin C contains one residue of divinyl ether (ω5Z)-etherolenic acid and one α-linolenate residue at sn-1 and sn-2 positions, respectively. Linolipin D possesses two (ω5Z)-etherolenic acid residues at both sn-1 and sn-2 positions. The rapid formation (2-30min) of linolipins C and D alongside with linolipins A and B occurred in the flax leaves upon their damage by freezing-thawing.

POPULATION COMPOSITION, GENDER SPECIALIZATION, AND THE ADAPTIVE SIGNIFICANCE OF DISTYLY IN LINUM PERENNE (LINACEAE)

Spatial distribution, pollen-flow and the factors affecting seed-set were studied for a population of the distylous perennial Linum perenne L. during a single season. The morphs were spatially segregated at the site. Stigmatic pollen loads on long-style plants comprised 27 to 51 % legitimate pollen and on short-style plants 0 to 46% legitimate pollen. Most flowers received more legitimate pollen grains than the number theoretically required to fertilize the corresponding number of ovules. Intraflower pollinations accounted for a large proportion of individual stigma loads. There was a weak negative correlation between the distance of the nearest legitimate neighbour and the number of legitimate pollen grains recorded on the stigma. No relationship was established between either the proximity or proportion of legitimate neighbours and seed-set. Long-style plants produced less pollen and matured more seeds than short-style plants. It is suggested that, in the population studied, paternal (pollen) and maternal (seed) investment are unequally divided between the morphs. This may be a common theme associated with heterostyly in plants.