Switches in heterogamety are known to occur in both animals and plants. Although plant sex determination systems probably often evolved more recently than those in several well-studied animals, including mammals, and have had less time for switches to occur, we previously detected a switch in heterogamety in the plant genus Silene: section Otites has both female and male heterogamety, whereas S. latifolia and its close relatives, in a different section of the genus, Melandrium (subgenus Behenantha), all have male heterogamety. Here we analyse the evolution of sex chromosomes in section Otites, which is estimated to have evolved only about 0.55 MYA. Our study confirms female heterogamety in S. otites and newly reveals female heterogamety in S. borysthenica. Sequence analyses and genetic mapping show that the sex-linked regions of these two species are the same, but the region in S. colpophylla, a close relative with male heterogamety, is different. The sex chromosome pairs of S. colpophylla and S. otites each correspond to an autosome of the other species, and both differ from the XY pair in S. latifolia. Silene section Otites species are suitable for detailed studies of the events involved in such changes, and our phylogenetic analysis suggests a possible change from female to male heterogamety within this section. Our analyses suggest a possibility that has so far not been considered, change in heterogamety through hybridization, in which a male-determining chromosome from one species is introgressed into another one, and over-rides its previous sex-determining system.
Few cases of spontaneously horizontally transferred bacterial genes into plant genomes have been described to date. The occurrence of horizontally transferred genes from the T-DNA of Agrobacterium rhizogenes into the plant genome has been reported in the genus Nicotiana and in the species Linaria vulgaris. Here we compare patterns of evolution in one of these genes (a gene encoding mikimopine synthase, mis) following three different events of horizontal gene transfer (HGT). As this gene plays an important role in Agrobacterium, and there are known cases showing that genes from pathogens can acquire plant protection function, we hypothesised that in at least some of the studied species we will find signs of selective pressures influencing mis sequence. The mikimopine synthase (mis) gene evolved in a different manner in the branch leading to Nicotiana tabacum and N. tomentosiformis, in the branch leading to N. glauca and in the genus Linaria. Our analyses of the genus Linaria suggest that the mis gene began to degenerate soon after the HGT. In contrast, in the case of N. glauca, the mis gene evolved under significant selective pressures. This suggests a possible role of mikimopine synthase in current N. glauca and its ancestor(s). In N. tabacum and N. tomentosiformis, the mis gene has a common frameshift mutation that disrupted its open reading frame. Interestingly, our results suggest that in spite of the frameshift, the mis gene could evolve under selective pressures. This sequence may still have some regulatory role at the RNA level as suggested by coverage of this sequence by small RNAs in N. tabacum.
- MeSH
- Agrobacterium enzymologie genetika MeSH
- bakteriální proteiny klasifikace genetika metabolismus MeSH
- druhová specificita MeSH
- fylogeneze MeSH
- imidazoly metabolismus MeSH
- interakce hostitele a patogenu genetika MeSH
- Linaria genetika mikrobiologie MeSH
- molekulární evoluce MeSH
- molekulární sekvence - údaje MeSH
- oxidoreduktasy působící na CH-NH vazby klasifikace genetika metabolismus MeSH
- posunová mutace MeSH
- přenos genů horizontální * MeSH
- pyridiny metabolismus MeSH
- regulace genové exprese enzymů MeSH
- sekvence nukleotidů MeSH
- selekce (genetika) MeSH
- tabák klasifikace genetika mikrobiologie MeSH
- transformace genetická MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Some transposable elements (TEs) show extraordinary variance in abundance along sex chromosomes but the mechanisms responsible for this variance are unknown. Here, we studied Ogre long terminal repeat (LTR) retrotransposons in Silene latifolia, a dioecious plant with evolutionarily young heteromorphic sex chromosomes. Ogre elements are ubiquitous in the S. latifolia genome but surprisingly absent on the Y chromosome. Bacterial artificial chromosome (BAC) library analysis and fluorescence in situ hybridization (FISH) were used to determine Ogre structure and chromosomal localization. Next generation sequencing (NGS) data were analysed to assess the transcription level and abundance of small RNAs. Methylation of Ogres was determined by bisulphite sequencing. Phylogenetic analysis was used to determine mobilization time and selection forces acting on Ogre elements. We characterized three Ogre families ubiquitous in the S. latifolia genome. One family is nearly absent on the Y chromosome despite all the families having similar structures and spreading mechanisms. We showed that Ogre retrotransposons evolved before sex chromosomes appeared but were mobilized after formation of the Y chromosome. Our data suggest that the absence of one Ogre family on the Y chromosome may be caused by 24-nucleotide (24-nt) small RNA-mediated silencing leading to female-specific spreading. Our findings highlight epigenetic silencing mechanisms as potentially crucial factors in sex-specific spreading of some TEs, but other possible mechanisms are also discussed.
- MeSH
- chromozomy rostlin * MeSH
- DNA rostlinná * MeSH
- epigeneze genetická MeSH
- fylogeneze MeSH
- genom rostlinný * MeSH
- koncové repetice * MeSH
- molekulární evoluce * MeSH
- molekulární sekvence - údaje MeSH
- retroelementy * MeSH
- RNA rostlin MeSH
- sekvence nukleotidů MeSH
- Silene genetika MeSH
- umlčování genů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
The plant genus Silene has become a model for evolutionary studies of sex chromosomes and sex-determining mechanisms. A recent study performed in Silene colpophylla showed that dioecy and the sex chromosomes in this species evolved independently from those in Silene latifolia, the most widely studied dioecious Silene species. The results of this study show that the sex-determining system in Silene otites, a species related to S. colpophylla, is based on female heterogamety, a sex determination system that is unique among the Silene species studied to date. Our phylogenetic data support the placing of S. otites and S. colpophylla in the subsection Otites and the analysis of ancestral states suggests that the most recent common ancestor of S. otites and S. colpophylla was most probably dioecious. These observations imply that a switch from XX/XY sex determination to a ZZ/ZW system (or vice versa) occurred in the subsection Otites. This is the first report of two different types of heterogamety within one plant genus of this mostly nondioecious plant family.
- MeSH
- chromozomy rostlin genetika MeSH
- genetická variace MeSH
- kvantitativní znak dědičný MeSH
- molekulární evoluce * MeSH
- pohlavní chromozomy genetika MeSH
- procesy určující pohlaví genetika MeSH
- pyl genetika MeSH
- sexuální faktory MeSH
- Silene anatomie a histologie genetika fyziologie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
BACKGROUND: Prior to this study, no differences in gene expression between male and female dioecious plants in the vegetative state had been detected. Among dioecious plants displaying sexual dimorphism, Silene latifolia is one of the most studied species. Although many sexually dimorphic traits have been described in S. latifolia, all of them are quantitative, and they usually become apparent only after the initiation of flowering. RESULTS: We present RT-PCR-based evidence that in S. latifolia, sexual dimorphism in gene expression is present long before the initiation of flowering. We describe three ESTs that show sex-specific (two male specific and one female specific) transcription at the rosette stage before the first flowering season. CONCLUSIONS: To our knowledge, this study provides the first molecular evidence of early pre-flowering sexual dimorphism in angiosperms.
- MeSH
- DNA rostlinná genetika MeSH
- exprimované sekvenční adresy MeSH
- fylogeneze MeSH
- pohlavní dimorfismus MeSH
- polymerázová řetězová reakce s reverzní transkripcí MeSH
- regulace genové exprese u rostlin MeSH
- sekvenční analýza DNA MeSH
- Silene genetika růst a vývoj MeSH
- stanovení celkové genové exprese MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- MeSH
- financování organizované MeSH
- Publikační typ
- abstrakty MeSH
Here we compare gene orders on the Silene latifolia sex chromosomes. On the basis of the deletion mapping results (11 markers and 23 independent Y chromosome deletion lines used), we conclude that a part of the Y chromosome (covering a region corresponding to at least 23.9 cM on the X chromosome) has been inverted. The gradient in silent-site divergence suggests that this inversion took place after the recombination arrest in this region. Because recombination arrest events followed by Y chromosome rearrangements also have been found in the human Y chromosome, this process seems to be a general evolutionary pathway.
