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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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ASGR-based Maximum Parsimony tree. Maximum parsimony tree based on the sequence alignments generated from the ASGR in the present study. Numbers at the nodes show bootstrap values obtained.
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Figure 3: ASGR-based Maximum Parsimony tree. Maximum parsimony tree based on the sequence alignments generated from the ASGR in the present study. Numbers at the nodes show bootstrap values obtained.

Mentions: Eight primer pairs, previously identified as ASGR-linked in F1 populations where P. squamulatum and C. ciliaris were the apomictic parents, were tested on all species used in this study (Additional File 1). Only the primer pair p779/p780 which amplifies a portion of the ASGR-BBM-like gene resulted in amplification of all the apomictic species but none of the sexual species. Primers p779/p780 are located in the 4th and 7th exons of ASGR-BBM-like2 (EU559277) and amplify a region including 3 introns of 95 bp, 266 bp, and 154 bp. Based on ASGR-linked BAC clone sequencing, P. squamulatum and C. ciliaris have duplicated ASGR-BBM-like genes [38]. The p779/p780 primers amplify both copies, although polymorphism between copies cannot be detected in P. squamulatum while polymorphism is detectable in C. ciliaris. The present analysis could differentiate two copies of the ASGR-BBM-like gene in C. setigerus, P. orientale, P. mezianum and C. ciliaris. In P. orientale, accession PS12 did not show two copies while PS15 did. Among the two types of sequences obtained in C. ciliaris and C. setigerus, one showed similarity with P. squamulatum while the other sequence grouped with the other copy from Cenchrus (Figure 3).


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)

ASGR-based Maximum Parsimony tree. Maximum parsimony tree based on the sequence alignments generated from the ASGR in the present study. Numbers at the nodes show bootstrap values obtained.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: ASGR-based Maximum Parsimony tree. Maximum parsimony tree based on the sequence alignments generated from the ASGR in the present study. Numbers at the nodes show bootstrap values obtained.
Mentions: Eight primer pairs, previously identified as ASGR-linked in F1 populations where P. squamulatum and C. ciliaris were the apomictic parents, were tested on all species used in this study (Additional File 1). Only the primer pair p779/p780 which amplifies a portion of the ASGR-BBM-like gene resulted in amplification of all the apomictic species but none of the sexual species. Primers p779/p780 are located in the 4th and 7th exons of ASGR-BBM-like2 (EU559277) and amplify a region including 3 introns of 95 bp, 266 bp, and 154 bp. Based on ASGR-linked BAC clone sequencing, P. squamulatum and C. ciliaris have duplicated ASGR-BBM-like genes [38]. The p779/p780 primers amplify both copies, although polymorphism between copies cannot be detected in P. squamulatum while polymorphism is detectable in C. ciliaris. The present analysis could differentiate two copies of the ASGR-BBM-like gene in C. setigerus, P. orientale, P. mezianum and C. ciliaris. In P. orientale, accession PS12 did not show two copies while PS15 did. Among the two types of sequences obtained in C. ciliaris and C. setigerus, one showed similarity with P. squamulatum while the other sequence grouped with the other copy from Cenchrus (Figure 3).

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