Endoreplication
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In many plant species, somatic cell differentiation is accompanied by endoreduplication, a process during which cells undergo one or more rounds of DNA replication cycles in the absence of mitosis, resulting in nuclei with multiples of 2C DNA amounts (4C, 8C, 16C, etc.). In some orchids, a disproportionate increase in nuclear DNA contents has been observed, where successive endoreduplication cycles result in DNA amounts 2C + P, 2C + 3P, 2C + 7P, etc., where P is the DNA content of the replicated part of the 2C nuclear genome. This unique phenomenon was termed "progressively partial endoreplication" (PPE). We investigated processes behind the PPE in Ludisia discolor using flow cytometry (FCM) and Illumina sequencing. In particular, we wanted to determine whether chromatin elimination or incomplete genome duplication was involved, and to identify types of DNA sequences that were affected. Cell cycle analysis of root tip cell nuclei pulse-labeled with EdU revealed two cell cycles, one ending above the population of nuclei with 2C + P content, and the other with a typical "horseshoe" pattern of S-phase nuclei ranging from 2C to 4C DNA contents. The process leading to nuclei with 2C + P amounts therefore involves incomplete genome replication. Subsequent Illumina sequencing of flow-sorted 2C and 2C + P nuclei showed that all types of repetitive DNA sequences were affected during PPE; a complete elimination of any specific type of repetitive DNA was not observed. We hypothesize that PPE is part of a highly controlled transition mechanism from proliferation phase to differentiation phase of plant tissue development.
- MeSH
- buněčné jádro genetika MeSH
- endoreduplikace genetika MeSH
- genom rostlinný MeSH
- listy rostlin genetika MeSH
- mitóza genetika MeSH
- Orchidaceae genetika MeSH
- polyploidie MeSH
- průtoková cytometrie metody MeSH
- replikace DNA genetika MeSH
- vysoce účinné nukleotidové sekvenování metody MeSH
- Publikační typ
- časopisecké články MeSH
Nuclear genome size is an inherited quantitative trait of eukaryotic organisms with both practical and biological consequences. A detailed analysis of major families is a promising approach to fully understand the biological meaning of the extensive variation in genome size in plants. Although Orchidaceae accounts for ∼10% of the angiosperm diversity, the knowledge of patterns and dynamics of their genome size is limited, in part due to difficulties in flow cytometric analyses. Cells in various somatic tissues of orchids undergo extensive endoreplication, either whole-genome or partial, and the G1-phase nuclei with 2C DNA amounts may be lacking, resulting in overestimated genome size values. Interpretation of DNA content histograms is particularly challenging in species with progressively partial endoreplication, in which the ratios between the positions of two neighboring DNA peaks are lower than two. In order to assess distributions of nuclear DNA amounts and identify tissue suitable for reliable estimation of nuclear DNA content, we analyzed six different tissue types in 48 orchid species belonging to all recognized subfamilies. Although traditionally used leaves may provide incorrect C-values, particularly in species with progressively partial endoreplication, young ovaries and pollinaria consistently yield 2C and 1C peaks of their G1-phase nuclei, respectively, and are, therefore, the most suitable parts for genome size studies in orchids. We also provide new DNA C-values for 22 orchid genera and 42 species. Adhering to the proposed methodology would allow for reliable genome size estimates in this largest plant family. Although our research was limited to orchids, the need to find a suitable tissue with dominant 2C peak of G1-phase nuclei applies to all endopolyploid species.
In angiosperms, genome size and nucleobase composition (GC content) exhibit pronounced variation with possible adaptive consequences. The hyperdiverse orchid family possessing the unique phenomenon of partial endoreplication (PE) provides a great opportunity to search for interactions of both genomic traits with the evolutionary history of the family. Using flow cytometry, we report values of both genomic traits and the type of endoreplication for 149 orchid species and compare these with a suite of life-history traits and climatic niche data using phylogeny-based statistics. The evolution of genomic traits was further studied using the Brownian motion (BM) and Ornstein-Uhlenbeck (OU) models to access their adaptive potential. Pronounced variation in genome size (341-54 878 Mb), and especially in GC content (23.9-50.5%), was detected among orchids. Diversity in both genomic traits was closely related to the type of endoreplication, plant growth form and climatic conditions. GC content was also associated with the type of dormancy. In all tested scenarios, OU models always outperformed BM models. Unparalleled GC content variation was discovered in orchids, setting new limits for plants. Our study indicates that diversity in both genome size and GC content has adaptive consequences and is tightly linked with evolutionary transitions to PE.
INTRODUCTION: Reproductive isolation and hybrid sterility are mechanisms that maintain the genetic integrity of species and prevent the introgression of heterospecific genes. However, crosses of closely related species can lead to complex evolution, such as the formation of all-female lineages that reproduce clonally. Bighead catfish (Clarias macrocephalus) and North African catfish (C. gariepinus) diverged 40 million years ago. They are cultivated and hybridized in Thailand for human consumption. Male hybrids are sterile due to genome-wide chromosome asynapsis during meiosis. Although female hybrids are sometimes fertile, their chromosome configuration during meiosis has not yet been studied. METHODS: We analyzed meiosis in the hybrid female catfish at pachytene (synaptonemal complexes) and diplotene (lampbrush chromosomes), using immunostaining to detect chromosome pairing and double-stranded break formation, and FISH with species-specific satellite DNAs to distinguish the parental chromosomes. RESULTS: More than 95% of oocytes exhibited chromosome asynapsis in female hybrid catfish; however, they were able to progress to the diplotene stage and form mature eggs. The remaining oocytes underwent premeiotic endoreplication, followed by synapsis and crossing over between sister chromosomes, similar to known clonal lineages in fish and reptiles. DISCUSSION: The occurrence of clonal reproduction in female hybrid catfish suggests a unique model for studying gametogenic alterations caused by hybridization and their potential for asexual reproduction. Our results further support the view that clonal reproduction in certain hybrid animals relies on intrinsic mechanisms of sexually reproducing parental species, given their multiple independent origins with the same mechanism.
- Publikační typ
- časopisecké články MeSH
BACKGROUND AND AIMS: Patterns of ploidy variation among and within populations can provide valuable insights into the evolutionary mechanisms shaping the dynamics of plant systems showing ploidy diversity. Whereas data on majority ploidies are, by definition, often sufficiently extensive, much less is known about the incidence and evolutionary role of minority cytotypes. METHODS: Ploidy and proportions of endoreplicated genome were determined using DAPI (4',6-diamidino-2-phenylindole) flow cytometry in 6150 Gymnadenia plants (fragrant orchids) collected from 141 populations in 17 European countries. All widely recognized European species, and several taxa of less certain taxonomic status were sampled within Gymnadenia conopsea sensu lato. KEY RESULTS: Most Gymnadenia populations were taxonomically and/or ploidy heterogeneous. Two majority (2x and 4x) and three minority (3x, 5x and 6x) cytotypes were identified. Evolution largely proceeded at the diploid level, whereas tetraploids were much more geographically and taxonomically restricted. Although minority ploidies constituted <2 % of the individuals sampled, they were found in 35 % of populations across the entire area investigated. The amount of nuclear DNA, together with the level of progressively partial endoreplication, separated all Gymnadenia species currently widely recognized in Europe. CONCLUSIONS: Despite their low frequency, minority cytotypes substantially increase intraspecific and intrapopulation ploidy diversity estimates for fragrant orchids. The cytogenetic structure of Gymnadenia populations is remarkably dynamic and shaped by multiple evolutionary mechanisms, including both the ongoing production of unreduced gametes and heteroploid hybridization. Overall, it is likely that the level of ploidy heterogeneity experienced by most plant species/populations is currently underestimated; intensive sampling is necessary to obtain a holistic picture.
- MeSH
- biologická evoluce * MeSH
- chromozomy rostlin genetika MeSH
- cytogenetika MeSH
- endoreduplikace MeSH
- genetická variace * MeSH
- genom rostlinný genetika MeSH
- hybridizace genetická MeSH
- Orchidaceae klasifikace cytologie genetika MeSH
- polyploidie * MeSH
- průtoková cytometrie MeSH
- zeměpis MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Evropa MeSH
Dark-induced growth (skotomorphogenesis) is primarily characterized by rapid elongation of the hypocotyl. We have studied the role of abscisic acid (ABA) during the development of young tomato (Solanum lycopersicum L.) seedlings. We observed that ABA deficiency caused a reduction in hypocotyl growth at the level of cell elongation and that the growth in ABA-deficient plants could be improved by treatment with exogenous ABA, through which the plants show a concentration dependent response. In addition, ABA accumulated in dark-grown tomato seedlings that grew rapidly, whereas seedlings grown under blue light exhibited low growth rates and accumulated less ABA. We demonstrated that ABA promotes DNA endoreduplication by enhancing the expression of the genes encoding inhibitors of cyclin-dependent kinases SlKRP1 and SlKRP3 and by reducing cytokinin levels. These data were supported by the expression analysis of the genes which encode enzymes involved in ABA and CK metabolism. Our results show that ABA is essential for the process of hypocotyl elongation and that appropriate control of the endogenous level of ABA is required in order to drive the growth of etiolated seedlings.
- MeSH
- cyklin-dependentní kinasy antagonisté a inhibitory MeSH
- cytokininy biosyntéza metabolismus MeSH
- endoreduplikace účinky záření MeSH
- homeostáza účinky záření MeSH
- hypokotyl cytologie růst a vývoj metabolismus účinky záření MeSH
- inhibitory proteinkinas farmakologie MeSH
- klíčení účinky léků účinky záření MeSH
- kyselina abscisová metabolismus MeSH
- Solanum lycopersicum cytologie růst a vývoj metabolismus účinky záření MeSH
- tma * MeSH
- vývoj rostlin účinky léků účinky záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Light is one of the most important factor influencing plant growth and development all through their life cycle. One of the well-known light-regulated processes is de-etiolation, i.e. the switch from skotomorphogenesis to photomorphogenesis. The hormones cytokinins (CKs) play an important role during the establishment of photomorphogenesis as exogenous CKs induced photomorphogenesis of dark-grown seedlings. Most of the studies are conducted on the plant model Arabidopsis, but no or few information are available for important crop species, such as tomato (Solanum lycopersicum L.). In our study, we analyzed for the first time the endogenous CKs content in tomato hypocotyls during skotomorphogenesis, photomorphogenesis and de-etiolation. For this purpose, two tomato genotypes were used: cv. Rutgers (wild-type; WT) and its corresponding mutant (7B-1) affected in its responses to blue light (BL). Using physiological and molecular approaches, we identified that the skotomorphogenesis is characterized by an endoreduplication-mediated cell expansion, which is inhibited upon BL exposure as seen by the accumulation of trancripts encoding CycD3, key regulators of the cell cycle. Our study showed for the first time that iP (isopentenyladenine) is the CK accumulated in the tomato hypocotyl upon BL exposure, suggesting its specific role in photomorphogenesis. This result was supported by physiological experiments and gene expression data. We propose a common model to explain the role and the relationship between CKs, namely iP, and endoreduplication during de-etiolation and photomorphogenesis.
- MeSH
- buněčný cyklus účinky léků genetika MeSH
- cyklin D3 genetika metabolismus MeSH
- cytokininy metabolismus MeSH
- endoreduplikace fyziologie účinky záření MeSH
- fylogeneze MeSH
- hypokotyl fyziologie účinky záření MeSH
- isopentenyladenosin metabolismus MeSH
- morfogeneze fyziologie účinky záření MeSH
- ploidie MeSH
- rostlinné proteiny genetika metabolismus MeSH
- semenáček fyziologie účinky záření MeSH
- Solanum lycopersicum fyziologie účinky záření MeSH
- světlo MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Hybrid sterility is a hallmark of speciation, but the underlying molecular mechanisms remain poorly understood. Here, we report that speciation may regularly proceed through a stage at which gene flow is completely interrupted, but hybrid sterility occurs only in male hybrids whereas female hybrids reproduce asexually. We analyzed gametogenic pathways in hybrids between the fish species Cobitis elongatoides and C. taenia, and revealed that male hybrids were sterile owing to extensive asynapsis and crossover reduction among heterospecific chromosomal pairs in their gametes, which was subsequently followed by apoptosis. We found that polyploidization allowed pairing between homologous chromosomes and therefore partially rescued the bivalent formation and crossover rates in triploid hybrid males. However, it was not sufficient to overcome sterility. In contrast, both diploid and triploid hybrid females exhibited premeiotic genome endoreplication, thereby ensuring proper bivalent formation between identical chromosomal copies. This endoreplication ultimately restored female fertility but it simultaneously resulted in the obligate production of clonal gametes, preventing any interspecific gene flow. In conclusion, we demonstrate that the emergence of asexuality can remedy hybrid sterility in a sex-specific manner and contributes to the speciation process.
- MeSH
- biologická evoluce MeSH
- chromozomy MeSH
- hybridní buňky cytologie fyziologie MeSH
- infertilita genetika MeSH
- meióza * MeSH
- partenogeneze * MeSH
- ryby genetika fyziologie MeSH
- vznik druhů (genetika) * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Hybridogenesis is a hemiclonal reproductive strategy in diploid and triploid hybrids. Our study model is a frog P. esculentus (diploid RL and triploids RLL and RRL), a natural hybrid between P. lessonae (LL) and P. ridibundus (RR). Hybridogenesis relies on elimination of one genome (L or R) from gonocytes (G) in tadpole gonads during prespermatogenesis, but not from spermatogonial stem cells (SSCs) in adults. Here we provide the first comprehensive study of testis morphology combined with chromosome composition in the full spectrum of spermatogenic cells. Using genomic in situ hybridization (GISH) and FISH we determined genomes in metaphase plates and interphase nuclei in Gs and SSCs. We traced genomic composition of SSCs, spermatocytes and spermatozoa in individual adult males that were crossed with females of the parental species and gave progeny. Degenerating gonocytes (24%-39%) and SSCs (18%-20%) led to partial sterility of juvenile and adult gonads. We conclude that elimination and endoreplication not properly completed during prespermatogenesis may be halted when gonocytes become dormant in juveniles. After resumption of mitotic divisions by SSCs in adults, these 20% of cells with successful genome elimination and endoreplication continue spermatogenesis, while in about 80% spermatogenesis is deficient. Majority of abnormal cells are eliminated by cell death, however some of them give rise to aneuploid spermatocytes and spermatozoa which shows that hybridogenesis is a wasteful process.
- Publikační typ
- časopisecké články MeSH
Entry into mitosis occurs after activation of Cdk1, resulting in chromosome condensation in the nucleus and centrosome separation, as well as increased microtubule nucleation activity in the cytoplasm. The active cyclin-B1-Cdk1 complex first appears at the centrosome, suggesting that the centrosome may facilitate the activation of mitotic regulators required for the commitment of cells to mitosis. However, the signalling pathways involved in controlling the initial activation of Cdk1 at the centrosome remain largely unknown. Here, we show that human Chk1 kinase localizes to interphase, but not mitotic, centrosomes. Chemical inhibition of Chk1 resulted in premature centrosome separation and activation of centrosome-associated Cdk1. Forced immobilization of kinase-inactive Chk1 to centrosomes also resulted in premature Cdk1 activation. Conversely, under such conditions wild-type Chk1 impaired activation of centrosome-associated Cdk1, thereby resulting in DNA endoreplication and centrosome amplification. Activation of centrosomal Cdk1 in late prophase seemed to be mediated by cytoplasmic Cdc25B, whose activity is controlled by centrosome-associated Chk1. These results suggest that centrosome-associated Chk1 shields centrosomal Cdk1 from unscheduled activation by cytoplasmic Cdc25B, thereby contributing to proper timing of the initial steps of cell division, including mitotic spindle formation.
- MeSH
- aktivace enzymů MeSH
- aparát dělícího vřeténka MeSH
- buněčné dělení MeSH
- buněčné linie MeSH
- centrozom * enzymologie MeSH
- cyklin B metabolismus MeSH
- cyklin B1 MeSH
- cykliny * metabolismus MeSH
- fosfatasy cdc25 fyziologie MeSH
- interfáze MeSH
- konfokální mikroskopie MeSH
- lidé MeSH
- proteinkinasa CDC2 fyziologie metabolismus MeSH
- proteinkinasy fyziologie metabolismus MeSH
- proteiny buněčného cyklu fyziologie MeSH
- vazba proteinů MeSH
- Check Tag
- lidé MeSH
