1,721,021 research outputs found
Transient Activation of Apomixis in Sexual Neotriploids May Retain Genomically Altered States and Enhance Polyploid Establishment
No full textPolyploid genomes evolve and follow a series of dynamic transfigurations along with adaptation and speciation. The initial formation of a new polyploid individual within a diploid population usually involves a triploid bridge, a two-step mechanism of cell fusions between ubiquitous (reduced) and rare (unreduced) gametes. The primary fusion event creates an intermediate triploid individual with unbalanced genome sets, a situation of genomic-shock characterized by gene expression dysregulation, high dosage sensitivity, disturbed cell divisions, and physiological and reproductive attributes drastically altered. This near-sterile neotriploid must produce (even) eupolyploids through secondary fusion events to restore genome steadiness, meiotic balance, and fertility required for the demographic establishment of a nascent lineage. Natural conditions locate several difficulties to polyploid establishment, including the production of highly unbalanced and rarely unreduced (euploid) gametes, frequency-dependent disadvantages (minority cytotype exclusion), severe fitness loss, and ecological competition with diploid parents. Persistence and adaptation of neopolyploids depend upon genetic and phenotypic novelty coupled to joint selective forces that preserve shock-induced genomic changes (subgenome homeolog partitioning) and drive meiotic (reproductive) stabilization and ecological diversification. Thus, polyploid establishment through the triploid bridge is a feasible but not ubiquitous process that requires a number of low-probability events and singular circumstances. Yet, frequencies of polyploids suggest that polyploid establishment is a pervasive process. To explain this disparity, and supported in experimental evidence, I propose that situations like hybridization and ploidy-state transitions associated to genomic shock and substantial developmental alterations can transiently activate apomixis as a mechanism to halt genomic instability and cancel factors restraining neopolyploid’s sexual fertility, particularly in triploids. Apomixis –as a temporal alternative to sex– skip meiosis and syngamy, and thus can freeze genomic attributes, avoid unbalanced chromosomal segregation and increase the formation of unreduced euploid gametes, elude frequency-dependent reproductive disadvantages by parthenogenetic development of the embryo and permissive development of endosperm during seed formation, and increase the effective population size of the neopolyploid lineage favoring the formation rate of eupolyploids compared to aneuploids. The subsequent action of genome resilience mechanisms that alleviate transcriptomic shock and selection upon gene interactions might restore a stable meiosis and sexual fertility within few generations, as observed in synthetic polyploids. Alternatively, provided that resilience mechanisms fail, the neopolyploid might retain apomixis and hold genomically and transcriptionally altered states for many generations
Competition between meiotic and apomictic pathways during ovule and seed development results in clonality
Full text linkMeiotic and apomictic reproductive pathways develop simultaneously in facultative aposporous apomictic species, and compete to form a seed as final goal. This developmental competition was evaluated in tetraploid genotypes of Paspalum malacophyllum in order to understand the scanty rate of sexuality in facultative apomictic populations. Cyto-embryology on ovules, flow cytometry on seeds and progeny tests by DNA fingerprinting were used to measure the relative incidence of each meiotic or apomictic pathway along four different stages of the plant's life cycle, namely the beginning and end of gametogenesis, seed formation, and adult offspring. A high variation in the frequencies of sexual and apomictic pathways occurred at the first two stages. A trend of radical decline in realised sexuality was then observed. Sexual and apomictic seeds were produced, but the efficiency of the sexual pathway drastically dropped, and exclusively clonal offspring remained. Both reproductive pathways are unstable at the beginning of development, and only the apomictic one remains functional. Key factors reducing sexuality are the faster growth and parthenogenetic development of the aposporous pathway, and an (epi)genetically negative background related to the extensive gene de-regulation pattern responsible for apomixis. The effects of inbreeding depression during post-fertilisation development may further decrease frequencies of effective sexuality.Fil: Hojsgaard, Diego Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; University of Goettingen. Department of Systematic Botany. Albrecht-von-Haller Institute of Plant Sciences; Alemania;Fil: Martínez, Eric Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina;Fil: Quarin, Camilo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentina
Single Independent Autopolyploidization Events From Distinct Diploid Gene Pools and Residual Sexuality Support Range Expansion of Locally Adapted Tetraploid Genotypes in a South American Grass
No full textPolyploidy plays a major role in plant evolution. The establishment of new polyploids is often a consequence of a single or few successful polyploidization events occurring within a species' evolutionary trajectory. New polyploid lineages can play different roles in plant diversification and go through several evolutionary stages influenced by biotic and abiotic constraints and characterized by extensive genetic changes. The study of such changes has been crucial for understanding polyploid evolution. Here, we use the multiploid-species Paspalum intermedium to study population-level genetic and morphological variation and ecological differentiation in polyploids. Using flow cytometry, amplified fragment length polymorphism (AFLP) genetic markers, environmental variables, and morphological data, we assessed variations in ploidy, reproductive modes, and the genetic composition in 35 natural populations of P. intermedium along a latitudinal gradient in South America. Our analyses show that apomictic auto-tetraploids are of multiple independent origin. While overall genetic variation was higher in diploids, both diploids and tetraploids showed significant variation within and among populations. The spatial distribution of genetic variation provides evidence for a primary origin of the contact zone between diploids and tetraploids and further supports the hypothesis of geographic displacement between cytotypes. In addition, a strong link between the ecological differentiation of cytotypes and spatial distribution of genetic variation was observed. Overall, the results indicate that polyploidization in P. intermedium is a recurrent phenomenon associated to a shift in reproductive mode and that multiple polyploid lineages from genetically divergent diploids contributed to the successful establishment of local polyploid populations and dispersal into new environments.</p>
Unravelling the ambiguous reproductive biology of Paspalum malacophyllum: a decades old story clarified
Full text linkIn a recent manuscript published by our group we analyzed the reproductive biology of the grass Paspalum malacophyllum by using traditional embryological techniques combined with current cytological and molecular methods. Our findings confirmed apparent contradictions regarding the reproductive behavior of P. malacophyllum from six independently published reports over the past six decades. Herein we summarize the main findings, conclusions, and validations of all previous studies, highlighting the need for multiple approaches to characterize reproductive systems when using apomictic plants in a breeding program.Fil: Hojsgaard, Diego Hernan. Universitat of Gottingen; AlemaniaFil: Burson, B. L.. Texas A&M University; Estados Unidos. United States Department of Agriculture; Estados UnidosFil: Quarin, Camilo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; ArgentinaFil: Martínez, Eric Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Instituto de Botánica del Nordeste (i); Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias; Argentin
Molecular Basis of Apomixis in Plants
No full textSexual reproduction in plants is a complex, stringently regulated process that leads to the creation of diaspores for a new generation: sexual seeds [...
Apomixis Technology: Separating the Wheat from the Chaff
No full textProjections indicate that current plant breeding approaches will be unable to incorporate the global crop yields needed to deliver global food security. Apomixis is a disruptive innovation by which a plant produces clonal seeds capturing heterosis and gene combinations of elite phenotypes. Introducing apomixis into hybrid cultivars is a game-changing development in the current plant breeding paradigm that will accelerate the generation of high-yield cultivars. However, apomixis is a developmentally complex and genetically multifaceted trait. The central problem behind current constraints to apomixis breeding is that the genomic configuration and molecular mechanism that initiate apomixis and guide the formation of a clonal seed are still unknown. Today, not a single explanation about the origin of apomixis offer full empirical coverage, and synthesizing apomixis by manipulating individual genes has failed or produced little success. Overall evidence suggests apomixis arise from a still unknown single event molecular mechanism with multigenic effects. Disentangling the genomic basis and complex genetics behind the emergence of apomixis in plants will require the use of novel experimental approaches benefiting from Next Generation Sequencing technologies and targeting not only reproductive genes, but also the epigenetic and genomic configurations associated with reproductive phenotypes in homoploid sexual and apomictic carriers. A comprehensive picture of most regulatory changes guiding apomixis emergence will be central for successfully installing apomixis into the target species by exploiting genetic modification techniques
The evolution of apomixis in angiosperms: A reappraisal
No full textApomixis, the asexual reproduction via seed, has long been regarded a blind alley of evolution. This hypothesis was based on the assumption that apomixis is an irreversible, phylogenetically derived trait that would rapidly lead to extinction of the respective lineages. However, recent updates of the taxonomic distribution of apomixis in angiosperms suggest an alternative evolutionary scenario. Apomixis is taxonomically scattered and occurs in both early and late branching lineages, with several reversals from apomixis to obligate sex along phylogeny. Genetic control of apomixis is based on altered expression patterns of the same genes that control sexual development; epigenetic changes following polyploidization and/or hybridization may trigger shifts from sexuality to apomixis. Mendelian inheritance confirms the facultative nature and possible reversibility of apomixis to sexual reproduction. Apomixis, therefore, could represent a transition period in the evolution of polyploid complexes, with polyspory in paleopolyploids being a remnant of lost apomixis. In neopolyploids, apomixis helps to overcome sterility and allows for geographical range expansions of agamic polyploid complexes. The facultative nature of apomixis allows for reversal to sexuality and further speciation of paleopolyploid lineages. Thus, apomixis may facilitate diversification of polyploid complexes and evolution in angiosperms.Austrian Austrian Science Fund [I310-B16
A novel indicator of karyotype evolution in the tribe Leucocoryneae (Allioideae, Amaryllidaceae)
Full text linkThe tribe Leucocoryneae is taxonomically andcytogenetically complex, mainly due to its extraordinarymorphological and karyological variation. Robertsoniantranslocations had long been recognized as a central factorcontributing to karyotype diversity within the Leucocoryneae,but so far no major tendency prevailing on theobserved complexity of karyotype formula among specieshas been identified. The assessment of nuclear DNAcontents by flow cytometry using propidium iodide in 23species, representing all genera within the tribe, showed amonoploid genome size variation of 1Cx = 9.07?30.46 pgdenoting a threefolds fluctuation. A highly significant linearassociation between the average DNA content per chromosomearm (2C/FN) and the monoploid genome size (1Cx)is reported for the first time and identified as a novel indicatorof a trend governing karyotype diversity within Leucocoryneae.This trend shows that a reduction in DNA contentper chromosome arm is influencing and has shaped karyotypeevolution of different monophyletic groups within thetribe despite the complex karyotype diversity and apparentlycontrasting patterns of genome sizes.Fil: Sassone, Agostina Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: López, Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Hojsgaard, Diego Hernan. Goethe Universitat Frankfurt; AlemaniaFil: Giussani, Liliana Mónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; Argentin
The evolution of apomixis in angiosperms: A reappraisal
No full textApomixis, the asexual reproduction via seed, has long been regarded a blind alley of evolution. This hypothesis was based on the assumption that apomixis is an irreversible, phylogenetically derived trait that would rapidly lead to extinction of the respective lineages. However, recent updates of the taxonomic distribution of apomixis in angiosperms suggest an alternative evolutionary scenario. Apomixis is taxonomically scattered and occurs in both early and late branching lineages, with several reversals from apomixis to obligate sex along phylogeny. Genetic control of apomixis is based on altered expression patterns of the same genes that control sexual development; epigenetic changes following polyploidization and/or hybridization may trigger shifts from sexuality to apomixis. Mendelian inheritance confirms the facultative nature and possible reversibility of apomixis to sexual reproduction. Apomixis, therefore, could represent a transition period in the evolution of polyploid complexes, with polyspory in paleopolyploids being a remnant of lost apomixis. In neopolyploids, apomixis helps to overcome sterility and allows for geographical range expansions of agamic polyploid complexes. The facultative nature of apomixis allows for reversal to sexuality and further speciation of paleopolyploid lineages. Thus, apomixis may facilitate diversification of polyploid complexes and evolution in angiosperms.Austrian Austrian Science Fund [I310-B16
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