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Evolution of the apomixis transmitting chromosome in Pennisetum.

Akiyama Y, Goel S, Conner JA, Hanna WW, Yamada-Akiyama H, Ozias-Akins P - BMC Evol. Biol. (2011)

Bottom Line: Apomixis is an intriguing trait in plants that results in maternal clones through seed reproduction.Our results indicate that the Apospory-Specific Genomic Region is shared by all apomictic species while it is absent from all sexual species or cytotypes.Contrary to our previous observations in Pennisetum squamulatum and Cenchrus ciliaris, retrotransposon sequences of the Opie-2-like family were not closely associated with the Apospory-Specific Genomic Region in all apomictic species, suggesting that they may have been accumulated after the Apospory-Specific Genomic Region originated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Horticulture, The University of Georgia, 2360 Rainwater Rd,, Tifton, GA 31793-5766, USA.

ABSTRACT

Background: Apomixis is an intriguing trait in plants that results in maternal clones through seed reproduction. Apomixis is an elusive, but potentially revolutionary, trait for plant breeding and hybrid seed production. Recent studies arguing that apomicts are not evolutionary dead ends have generated further interest in the evolution of asexual flowering plants.

Results: In the present study, we investigate karyotypic variation in a single chromosome responsible for transmitting apomixis, the Apospory-Specific Genomic Region carrier chromosome, in relation to species phylogeny in the genera Pennisetum and Cenchrus. A 1 kb region from the 3' end of the ndhF gene and a 900 bp region from trnL-F were sequenced from 12 apomictic and eight sexual species in the genus Pennisetum and allied genus Cenchrus. An 800 bp region from the Apospory-Specific Genomic Region also was sequenced from the 12 apomicts. Molecular cytological analysis was conducted in sixteen Pennisetum and two Cenchrus species. Our results indicate that the Apospory-Specific Genomic Region is shared by all apomictic species while it is absent from all sexual species or cytotypes. Contrary to our previous observations in Pennisetum squamulatum and Cenchrus ciliaris, retrotransposon sequences of the Opie-2-like family were not closely associated with the Apospory-Specific Genomic Region in all apomictic species, suggesting that they may have been accumulated after the Apospory-Specific Genomic Region originated.

Conclusions: Given that phylogenetic analysis merged Cenchrus and newly investigated Pennisetum species into a single clade containing a terminal cluster of Cenchrus apomicts, the presumed monophyletic origin of Cenchrus is supported. The Apospory-Specific Genomic Region likely preceded speciation in Cenchrus and its lateral transfer through hybridization and subsequent chromosome repatterning may have contributed to further speciation in the two genera.

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Ordered chromosomes based on Giemsa- and DAPI-stained chromosomes of P. massaicum (PS680). These chromosomes are from the spreads of Figure 1j and k and were sorted according to their lengths. The bottom two rows of chromosomes are the eight that did not hybridize with BAC P602. Black and white arrow heads indicate ASGR and rDNA, respectively.
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Figure 7: Ordered chromosomes based on Giemsa- and DAPI-stained chromosomes of P. massaicum (PS680). These chromosomes are from the spreads of Figure 1j and k and were sorted according to their lengths. The bottom two rows of chromosomes are the eight that did not hybridize with BAC P602. Black and white arrow heads indicate ASGR and rDNA, respectively.

Mentions: The ASGR-carrier chromosome in P. massaicum (PS680) showed unique morphology among the species with a highly condensed region in the middle of the long arm (Figure 5). PS953, another P. massaicum accession, showed the same ASGR-carrier chromosome characteristics as PS680. The morphology of the ASGR-carrier chromosome was also sufficiently unique within this species such that it sometimes could be distinguished under phase contrast without Giemsa staining or FISH (Figure 4j, Figure 7). Comparison of the Giemsa-stained chromosomes having rDNA indicated that morphology was different among them (Figure 7).


Evolution of the apomixis transmitting chromosome in Pennisetum.

Akiyama Y, Goel S, Conner JA, Hanna WW, Yamada-Akiyama H, Ozias-Akins P - BMC Evol. Biol. (2011)

Ordered chromosomes based on Giemsa- and DAPI-stained chromosomes of P. massaicum (PS680). These chromosomes are from the spreads of Figure 1j and k and were sorted according to their lengths. The bottom two rows of chromosomes are the eight that did not hybridize with BAC P602. Black and white arrow heads indicate ASGR and rDNA, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198970&req=5

Figure 7: Ordered chromosomes based on Giemsa- and DAPI-stained chromosomes of P. massaicum (PS680). These chromosomes are from the spreads of Figure 1j and k and were sorted according to their lengths. The bottom two rows of chromosomes are the eight that did not hybridize with BAC P602. Black and white arrow heads indicate ASGR and rDNA, respectively.
Mentions: The ASGR-carrier chromosome in P. massaicum (PS680) showed unique morphology among the species with a highly condensed region in the middle of the long arm (Figure 5). PS953, another P. massaicum accession, showed the same ASGR-carrier chromosome characteristics as PS680. The morphology of the ASGR-carrier chromosome was also sufficiently unique within this species such that it sometimes could be distinguished under phase contrast without Giemsa staining or FISH (Figure 4j, Figure 7). Comparison of the Giemsa-stained chromosomes having rDNA indicated that morphology was different among them (Figure 7).

Bottom Line: Apomixis is an intriguing trait in plants that results in maternal clones through seed reproduction.Our results indicate that the Apospory-Specific Genomic Region is shared by all apomictic species while it is absent from all sexual species or cytotypes.Contrary to our previous observations in Pennisetum squamulatum and Cenchrus ciliaris, retrotransposon sequences of the Opie-2-like family were not closely associated with the Apospory-Specific Genomic Region in all apomictic species, suggesting that they may have been accumulated after the Apospory-Specific Genomic Region originated.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Horticulture, The University of Georgia, 2360 Rainwater Rd,, Tifton, GA 31793-5766, USA.

ABSTRACT

Background: Apomixis is an intriguing trait in plants that results in maternal clones through seed reproduction. Apomixis is an elusive, but potentially revolutionary, trait for plant breeding and hybrid seed production. Recent studies arguing that apomicts are not evolutionary dead ends have generated further interest in the evolution of asexual flowering plants.

Results: In the present study, we investigate karyotypic variation in a single chromosome responsible for transmitting apomixis, the Apospory-Specific Genomic Region carrier chromosome, in relation to species phylogeny in the genera Pennisetum and Cenchrus. A 1 kb region from the 3' end of the ndhF gene and a 900 bp region from trnL-F were sequenced from 12 apomictic and eight sexual species in the genus Pennisetum and allied genus Cenchrus. An 800 bp region from the Apospory-Specific Genomic Region also was sequenced from the 12 apomicts. Molecular cytological analysis was conducted in sixteen Pennisetum and two Cenchrus species. Our results indicate that the Apospory-Specific Genomic Region is shared by all apomictic species while it is absent from all sexual species or cytotypes. Contrary to our previous observations in Pennisetum squamulatum and Cenchrus ciliaris, retrotransposon sequences of the Opie-2-like family were not closely associated with the Apospory-Specific Genomic Region in all apomictic species, suggesting that they may have been accumulated after the Apospory-Specific Genomic Region originated.

Conclusions: Given that phylogenetic analysis merged Cenchrus and newly investigated Pennisetum species into a single clade containing a terminal cluster of Cenchrus apomicts, the presumed monophyletic origin of Cenchrus is supported. The Apospory-Specific Genomic Region likely preceded speciation in Cenchrus and its lateral transfer through hybridization and subsequent chromosome repatterning may have contributed to further speciation in the two genera.

Show MeSH