Diploid apomicts of the
            <i>Boechera holboellii</i>
            complex display large-scale chromosome substitutions and aberrant chromosomes

Kantama, Laksana; Sharbel, Timothy F.; Schranz, M. Eric; Mitchell-Olds, Thomas; Vries, Sven de; Jong, Hans de

doi:10.1073/pnas.0706647104

Cited by 107 publications

(155 citation statements)

References 32 publications

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“…However, the unequal number of homologous centromere classes could also be attributable to random segregational loss of parental chromosomes during a period of tetrasomic chromosome association in a genetic autopolyploid, or the newly formed polyploid Glycine could have been a segmental allopolyploid, with attributes of both auto-and allopolyploidy at different loci. One explanation for the observed centromeric structure in soybean would be some type of allopolyploidy followed by diploidization leading to a present day pseudodiploid, similar to what was recently hypothesized for Boechera holboellii (Kantama et al, 2007). Ultimately, the exact mode of origin and thus the formal distinction is less important than the observation that homologous variation currently exists in the Glycine genome, and that the soybean is a fixed polyploid hybrid for centromeres, as it is for many other loci.…”

Section: Discussionmentioning

confidence: 85%

Molecular and Chromosomal Evidence for Allopolyploidy in Soybean

et al. 2009

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Recent studies have documented that the soybean (Glycine max) genome has undergone two rounds of large-scale genome and/or segmental duplication. To shed light on the timing and nature of these duplication events, we characterized and analyzed two subfamilies of high-copy centromeric satellite repeats, CentGm-1 and CentGm-2, using a combination of computational and molecular cytogenetic approaches. These two subfamilies of satellite repeats mark distinct subsets of soybean centromeres and, in at least one case, a pair of homologs, suggesting their origins from an allopolyploid event. The satellite monomers of each subfamily are arranged in large tandem arrays, and intermingled monomers of the two subfamilies were not detected by fluorescence in situ hybridization on extended DNA fibers nor at the sequence level. This indicates that there has been little recombination and homogenization of satellite DNA between these two sets of centromeres. These satellite repeats are also present in Glycine soja, the proposed wild progenitor of soybean, but could not be detected in any other relatives of soybean examined in this study, suggesting the rapid divergence of the centromeric satellite DNA within the Glycine genus. Together, these observations provide direct evidence, at molecular and chromosomal levels, in support of the hypothesis that the soybean genome has experienced a recent allopolyploidization event.

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Section: Discussionmentioning

confidence: 85%

Molecular and Chromosomal Evidence for Allopolyploidy in Soybean

et al. 2009

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“…These findings indicate that neither chromosome depletion (except for that causing the removal of the segment homologous to maize 6L) nor maize genome addition can promote reversion towards sexuality, when endured by maize-Tripsacum chromosome complements proper for functional apomixis. Collectively, they suggest that apomixis responds little to genome plasticity, a behavior also documented recently in alloploid apomicts of the Boechera holboellii complex (Kantama et al, 2007). However, although the general mechanisms governing apomictic reproduction in maize-Tripsacum apomicts unlikely operate in a dosage dependent manner, the recurring reproductive shift between 6-1349 and its derivatives after genomic accumulation suggests that dosage dependency occurs to some extent and may account, at least partially, for variations in facultativeness commonly observed in apomictic species.…”

Section: Dna-content-based Progeny Tests In Apomictic Clones With Difmentioning

confidence: 88%

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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“…For example, a satellite chromosome is present in diplosporous Taraxacum, and the diplospory locus is thought to be located on this satellite chromosome (van Dijk and Bakx-Schotman, 2004). Karyotype analyses in diplosporous Boechera species have revealed large-scale chromosome substitutions and the presence of a highly heterochromatic chromosome that has been postulated to have a role in the genetic control of apomixis (Kantama et al, 2007). However, the association of genetic loci controlling diplosporous apomixis with these chromosomal features in Boechera and Taraxacum has not been confirmed.…”

Section: Convergent Evolution Of Chromosomes Containing Apospory Locimentioning

confidence: 99%

Chromosomes Carrying Meiotic Avoidance Loci in Three Apomictic Eudicot Hieracium Subgenus Pilosella Species Share Structural Features with Two Monocot Apomicts

et al. 2011

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The LOSS OF APOMEIOSIS (LOA) locus is one of two dominant loci known to control apomixis in the eudicot Hieracium praealtum. LOA stimulates the differentiation of somatic aposporous initial cells after the initiation of meiosis in ovules. Aposporous initial cells undergo nuclear proliferation close to sexual megaspores, forming unreduced aposporous embryo sacs, and the sexual program ceases. LOA-linked genetic markers were used to isolate 1.2 Mb of LOA-associated DNAs from H. praealtum. Physical mapping defined the genomic region essential for LOA function between two markers, flanking 400 kb of identified sequence and central unknown sequences. Cytogenetic and sequence analyses revealed that the LOA locus is located on a single chromosome near the tip of the long arm and surrounded by extensive, abundant complex repeat and transposon sequences. Chromosomal features and LOA-linked markers are conserved in aposporous Hieracium caespitosum and Hieracium piloselloides but absent in sexual Hieracium pilosella. Their absence in apomictic Hieracium aurantiacum suggests that meiotic avoidance may have evolved independently in aposporous subgenus Pilosella species. The structure of the hemizygous chromosomal region containing the LOA locus in the three Hieracium subgenus Pilosella species resembles that of the hemizygous apospory-specific genomic regions in monocot Pennisetum squamulatum and Cenchrus ciliaris. Analyses of partial DNA sequences at these loci show no obvious conservation, indicating that they are unlikely to share a common ancestral origin. This suggests convergent evolution of repeat-rich hemizygous chromosomal regions containing apospory loci in these monocot and eudicot species, which may be required for the function and maintenance of the trait.Asexual seed formation, or apomixis, occurs in both monocot and eudicot plants and has evolved in more than 40 plant genera. Approximately 75% of apomicts exist in three families, the Poaceae, Asteraceae, and Rosaceae. Apomixis bypasses meiosis during female gametophyte formation. This contrasts with sexual female gametophyte development, which requires the meiosis of a megaspore mother cell (MMC) in the ovule (megasporogenesis) followed by nuclear proliferation of typically one of the meiotic

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Diploid apomicts of the Boechera holboellii complex display large-scale chromosome substitutions and aberrant chromosomes

Cited by 107 publications

References 32 publications

Molecular and Chromosomal Evidence for Allopolyploidy in Soybean

Molecular and Chromosomal Evidence for Allopolyploidy in Soybean

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

Chromosomes Carrying Meiotic Avoidance Loci in Three Apomictic Eudicot Hieracium Subgenus Pilosella Species Share Structural Features with Two Monocot Apomicts

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