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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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Physical mapping with ASGR-linked BACs on chromosome spreads from various Pennisetum and Cenchrus species. a-j, Color-merged images of FISH signals and inverted DAPI-stained chromosomes; red and green arrows indicate P001 and P208, respectively; insets show enlarged, pseudo-colored ASGR-carrier chromosome. k-m, Images of dual-labeled FISH on DAPI-stained chromosomes. a, m: P. mezianum (PS9); b: P. orientale (PS12); c: C. setigerus (PS16); d: P. polystachion (PS19); e: P. setaceum (PS25); f: P. flaccidum (PS95); g: P. subangustum (PS163); h: P. villosum (PS249); i: P. pedicillatum (PS304); j: P. massaicum; k: P. massaicum spread in panel j stripped and rehybridized with rDNA and P602 (red); green arrows and signals indicate rDNA; outlined chromosomes did not hybridize with P602. l: C. setigerus hybridized with rDNA and P208; green signals are rDNA and red arrow indicates P208 signal. m: P. mezianum (PS9) hybridized with P208 (red arrow) and P602 (green signal). Bars correspond to 10 μm.
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Figure 4: Physical mapping with ASGR-linked BACs on chromosome spreads from various Pennisetum and Cenchrus species. a-j, Color-merged images of FISH signals and inverted DAPI-stained chromosomes; red and green arrows indicate P001 and P208, respectively; insets show enlarged, pseudo-colored ASGR-carrier chromosome. k-m, Images of dual-labeled FISH on DAPI-stained chromosomes. a, m: P. mezianum (PS9); b: P. orientale (PS12); c: C. setigerus (PS16); d: P. polystachion (PS19); e: P. setaceum (PS25); f: P. flaccidum (PS95); g: P. subangustum (PS163); h: P. villosum (PS249); i: P. pedicillatum (PS304); j: P. massaicum; k: P. massaicum spread in panel j stripped and rehybridized with rDNA and P602 (red); green arrows and signals indicate rDNA; outlined chromosomes did not hybridize with P602. l: C. setigerus hybridized with rDNA and P208; green signals are rDNA and red arrow indicates P208 signal. m: P. mezianum (PS9) hybridized with P208 (red arrow) and P602 (green signal). Bars correspond to 10 μm.

Mentions: The results of FISH with ASGR-linked BACs are summarized in Table 2 and Figs. 4 and 5. No sexual species showed discrete signals from hybridization of the ASGR-linked BACs P001, P109 or P208. BAC P208 showed weak signal on the centromeres of not only aposporous, but also sexual species. In aposporous species, the ASGR-linked BACs were detected as strong signals on a single chromosome (Figure 4a, c-j) with one exception (Figure 4b). In P. orientale (PS12), a 54-chromosome accession, two ASGR-carrier chromosomes were observed (Figure 4b). The BACs sometimes showed strong and spatially distinct signals within the ASGR indicating duplicated loci or repetitive sequences.


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)

Physical mapping with ASGR-linked BACs on chromosome spreads from various Pennisetum and Cenchrus species. a-j, Color-merged images of FISH signals and inverted DAPI-stained chromosomes; red and green arrows indicate P001 and P208, respectively; insets show enlarged, pseudo-colored ASGR-carrier chromosome. k-m, Images of dual-labeled FISH on DAPI-stained chromosomes. a, m: P. mezianum (PS9); b: P. orientale (PS12); c: C. setigerus (PS16); d: P. polystachion (PS19); e: P. setaceum (PS25); f: P. flaccidum (PS95); g: P. subangustum (PS163); h: P. villosum (PS249); i: P. pedicillatum (PS304); j: P. massaicum; k: P. massaicum spread in panel j stripped and rehybridized with rDNA and P602 (red); green arrows and signals indicate rDNA; outlined chromosomes did not hybridize with P602. l: C. setigerus hybridized with rDNA and P208; green signals are rDNA and red arrow indicates P208 signal. m: P. mezianum (PS9) hybridized with P208 (red arrow) and P602 (green signal). Bars correspond to 10 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Physical mapping with ASGR-linked BACs on chromosome spreads from various Pennisetum and Cenchrus species. a-j, Color-merged images of FISH signals and inverted DAPI-stained chromosomes; red and green arrows indicate P001 and P208, respectively; insets show enlarged, pseudo-colored ASGR-carrier chromosome. k-m, Images of dual-labeled FISH on DAPI-stained chromosomes. a, m: P. mezianum (PS9); b: P. orientale (PS12); c: C. setigerus (PS16); d: P. polystachion (PS19); e: P. setaceum (PS25); f: P. flaccidum (PS95); g: P. subangustum (PS163); h: P. villosum (PS249); i: P. pedicillatum (PS304); j: P. massaicum; k: P. massaicum spread in panel j stripped and rehybridized with rDNA and P602 (red); green arrows and signals indicate rDNA; outlined chromosomes did not hybridize with P602. l: C. setigerus hybridized with rDNA and P208; green signals are rDNA and red arrow indicates P208 signal. m: P. mezianum (PS9) hybridized with P208 (red arrow) and P602 (green signal). Bars correspond to 10 μm.
Mentions: The results of FISH with ASGR-linked BACs are summarized in Table 2 and Figs. 4 and 5. No sexual species showed discrete signals from hybridization of the ASGR-linked BACs P001, P109 or P208. BAC P208 showed weak signal on the centromeres of not only aposporous, but also sexual species. In aposporous species, the ASGR-linked BACs were detected as strong signals on a single chromosome (Figure 4a, c-j) with one exception (Figure 4b). In P. orientale (PS12), a 54-chromosome accession, two ASGR-carrier chromosomes were observed (Figure 4b). The BACs sometimes showed strong and spatially distinct signals within the ASGR indicating duplicated loci or repetitive sequences.

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
Related in: MedlinePlus