Apomixis: Developmental Characteristics and Genetics

Ozias‐Akins, Peggy

doi:10.1080/07352680600563926

Cited by 103 publications

(89 citation statements)

References 119 publications

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“…A cultivar Marandu foi liberada pela Embrapa em 1983, para atender a demanda por cultivares resistentes à cigarrinha-das-pastagens, e é hoje o capim mais plantado no Brasil (Araújo et al, 2008). A progênie resultante da reprodução apomítica é constituída por clones idênticos à planta-mãe (Ozias-Akins, 2006;Tucker & Koltunow, 2009), o que implica baixa diversidade genética. As únicas fontes de diversidade dessa população apomítica facultativa são mutações somáticas ou ocorrência de fecundação nos sacos embrionários do tipo Polygonum, característicos de plantas sexuais.…”

Section: Introductionunclassified

Histologia da embriogênese somática induzida em embriões de sementes maduras de Urochloa brizantha apomítica

Lenis-Manzano

Araújo

Valle

et al. 2010

Pesq. agropec. bras.

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Resumo -O objetivo deste trabalho foi descrever o processo de embriogênese somática em Urochloa brizantha cv. Marandu (Syn. Brachiaria brizantha cv. Marandu) e fornecer subsídios para o aprimoramento dos métodos de cultura de tecidos e transformação genética. Calos embriogênicos foram obtidos por indução em embriões isolados de sementes maduras, e cultivados in vitro, em meio de cultura que continha ácido 2,4-diclorofenoxiacético, 6-benzilaminopurina e caseína hidrolisada. Plântulas foram regeneradas a partir dos calos embriogênicos, na presença de ácido naftalenoacético e cinetina. Esse processo foi descrito morfologicamente por observações em microscopia de luz de secções seriadas semifinas de tecidos fixados, ao longo do processo de regeneração, em FAA [formaldeído (40%): ácido acético glacial: etanol (50%), a 5:5:90 v/v/v]. Os embriões das sementes de U. brizantha cv. Marandu não têm epiblasto e são classificados como do tipo panicoide. Nas condições estabelecidas de cultura in vitro, calos embriogênicos e embriões somáticos de U. brizantha cv. Marandu, desenvolvem-se a partir de células meristemáticas do escutelo.Termos para indexação: Brachiaria, cultura de tecidos, melhoramento de forrageiras, regeneração, transformação genética. Histology of somatic embryogenesis induced in embryos of mature seeds of the apomictic Urochloa brizanthaAbstract -The objective of this work was to describe the process of somatic embryogenesis in Urochloa brizantha cv. Marandu (Syn. Brachiaria brizantha cv. Marandu) and to provide support for the improvement of tissue culture and genetic transformation methods. Embryogenic calli were obtained by induction in embryos isolated from mature seeds, and cultivated in vitro in culture medium containing 2,4-dichlorophenoxyacetic acid, 6-benzylaminopurine and hydrolyzed casein. Plantlets were regenerated from the embryogenic calli in the presence of naphthaleneacetic acid and kinetin. This process was described by morphological observations of serial semithin sections of tissues fixed along the regeneration process in FAA (40% formaldehyde: acetic acid: 50% ethanol, at 5:5:90 v/v/v), using light microscopy. Seed embryos of U. brizantha cv. Marandu do not have epiblast and are classified as Panicum-type. Under in vitro culture conditions, embryogenic calli and somatic embryos of U. brizantha cv. Marandu develop from meristematic cells of the scutellum.

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Section: Introductionunclassified

Histologia da embriogênese somática induzida em embriões de sementes maduras de Urochloa brizantha apomítica

Lenis-Manzano

Araújo

Valle

et al. 2010

Pesq. agropec. bras.

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“…Hieracium subgenus pilosella, Poa, and Tripsacum, suggest that gametophytic apomixis (referred to as apomixis herein) relies upon either spatial or temporal misexpression of genes acting during female sexual reproduction (Albertini et al, 2004, Grimanelli et al, 2003, Tucker et al, 2003. However, although candidate genes showing differences in spatial and temporal expression patterns between apomicts and their sexual counterparts have been identified, both their involvement in the control of apomixis and function remain largely speculative (Ozias-Akins, 2006). Inheritance studies have provided a relatively simple view for the genetics of apomixis, which was reported to depend on a few dominant genes in most species investigated (Asker andJerling, 1992, Ozias-Akins andvan Dijk, 2007).…”

Section: Introductionmentioning

confidence: 99%

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Leblanc¹,

Grimanelli²,

Hernandez-Rodriguez³

et al. 2009

Int. J. Dev. Biol.

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Apomixis in plants covers a variety of cloning systems through seeds of great potential for plant breeding. Among long-standing approaches for crop improvement is the attempt to exploit wild relatives as natural, vast reservoirs for novel genetic variation. With regard to apomixis, maize possesses an apomictic wild relative, Tripsacum, which we used to produce advanced maize-Tripsacum hybrid generations. However, introgression of apomixis in maize has failed so far. In order to understand the how's and why's, we undertook characterization of seed development and inheritance studies in these materials. We show that apomictic seeds suffer from epigenetic loads. Both seed tissues, the endosperm and the embryo, displayed developmental defects resulting from imbalanced parental genomic contributions and aberrant methylation patterns, respectively. Progeny characterization of several maize-Tripsacum hybrid generations allowed significant progress toward the unraveling of the genetics of apomixis. First, chromosome deletion mapping showed that expression of apomixis requires one single Tripsacum chromosome. However, inheritance studies revealed that female gametes inheriting this segment were unequivalent carriers depending on their origin: unreduced gametes transmit a functional segment, whereas progeny derived from reduced ones reproduced sexually. Finally, chromosomal or genomic dosage variation barely affected the apomictic phenotype suggesting no dependency for ploidy in these materials. We conclude that epigenetic information imposes constraints for apomictic seed development and seems pivotal for transgenerational propagation of apomixis. The nature of the triggering mechanisms remains unknown as-yet, but it certainly explains the modest success relative to the development of apomictic maize thus far.

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“…Embryos develop from the unreduced eggs in the absence of fertilization (termed parthenogenesis) and endosperm formation occurs with or without fertilization. The progeny resulting from apomictic reproduction always retain a maternal genotype (Bicknell and Koltunow, 2004;Ozias-Akins, 2006).…”

Section: Introductionmentioning

confidence: 99%

Evolution of apomixis loci in Pilosella and Hieracium (Asteraceae) inferred from the conservation of apomixis-linked markers in natural and experimental populations

et al. 2014

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The Hieracium and Pilosella (Lactuceae, Asteraceae) genera of closely related hawkweeds contain species with two different modes of gametophytic apomixis (asexual seed formation). Both genera contain polyploid species, and in wild populations, sexual and apomictic species co-exist. Apomixis is known to co-exist with sexuality in apomictic Pilosella individuals, however, apomictic Hieracium have been regarded as obligate apomicts. Here, a developmental analysis of apomixis within 16 Hieracium species revealed meiosis and megaspore tetrad formation in 1 to 7% of ovules, for the first time indicating residual sexuality in this genus. Molecular markers linked to the two independent, dominant loci LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP) controlling apomixis in Pilosella piloselloides subsp. praealta were screened across 20 phenotyped Hieracium individuals from natural populations, and 65 phenotyped Pilosella individuals from natural and experimental cross populations, to examine their conservation, inheritance and association with reproductive modes. All of the tested LOA and LOP-linked markers were absent in the 20 Hieracium samples irrespective of their reproductive mode. Within Pilosella, LOA and LOP-linked markers were essentially absent within the sexual plants, although they were not conserved in all apomictic individuals. Both loci appeared to be inherited independently, and evidence for additional genetic factors influencing quantitative expression of LOA and LOP was obtained. Collectively, these data suggest independent evolution of apomixis in Hieracium and Pilosella and are discussed with respect to current knowledge of the evolution of apomixis.

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Apomixis: Developmental Characteristics and Genetics

Cited by 103 publications

References 119 publications

Histologia da embriogênese somática induzida em embriões de sementes maduras de Urochloa brizantha apomítica

Histologia da embriogênese somática induzida em embriões de sementes maduras de Urochloa brizantha apomítica

Seed development and inheritance studies in apomictic maize-Tripsacum hybrids reveal barriers for the transfer of apomixis into sexual crops

Evolution of apomixis loci in Pilosella and Hieracium (Asteraceae) inferred from the conservation of apomixis-linked markers in natural and experimental populations

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