RESUMO
Knowledge on the structure and distribution of genetic diversity is a key aspect to plan and execute an efficient conservation and utilization of the genetic resources of any crop as well as for determining historical demographic inferences. In this work, a large data set of 1,765 accessions of cherimoya (Annona cherimola Mill, Annonaceae), an underutilized fruit tree crop native to the Neotropics and used as a food source by pre-Columbian cultures, was collected from six different countries across the American continent and amplified with nine highly informative microsatellite markers. The structure analyses, fine representation of the genetic diversity and an ABC approach suggest a Mesoamerican origin of the crop, contrary to previous reports, with clear implications for the dispersion of plant germplasm between Central and South America in pre-Columbian times. These results together with the potential distribution of the species in a climatic change context using two different climate models provide new insights for the history and conservation of extant genetic resources of cherimoya that can be applied to other currently underutilized woody perennial crops.
Assuntos
Annona/genética , Conservação dos Recursos Naturais , Variação Genética , Genética Populacional , América Central , Evolução Molecular , Frutas , Repetições de Microssatélites , América do Sul , ÁrvoresRESUMO
The intron content of plant organellar genes is a useful marker in molecular systematics and evolution. We have tested representatives of a wide range of monocotyledonous plant families for the presence of an intron (cox2 intron 1) in one of the most conservative mitochondrial genes, the cox2 locus. Almost all species analyzed were found to harbor a group II intron at a phylogenetically conserved position. The only exceptions were members of a single monocot family, the Ruscaceae: representatives of all genera in this family were found to lack cox2 intron 1, but instead harbor an intron in the 3' portion of the cox2 coding region (cox2 intron 2). The presence of cox2 intron 1 in families of monocotyledonous plants that are closely related to the Ruscaceae suggests that loss of the intron is specific to this family and may have accompanied the evolutionary appearance of the Ruscaceae. Interestingly, sequences that are highly homologous to cox2 intron 2 are found in a nuclear intron in a lineage of monocotyledonous plants, suggesting that the originally mitochondrial group II intron sequence was transferred to the nuclear genome and reused there to build a spliceosomal intron.
Assuntos
Complexo IV da Cadeia de Transporte de Elétrons/genética , Genes de Plantas , Íntrons , Proteínas de Plantas/genética , Plantas/genética , Sequência de Aminoácidos , Sequência de Bases , Núcleo Celular/genética , DNA Mitocondrial/genética , DNA de Plantas/genética , Evolução Molecular , Magnoliopsida/enzimologia , Magnoliopsida/genética , Mitocôndrias/genética , Dados de Sequência Molecular , Plantas/enzimologia , Edição de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Plantas/genética , RNA de Plantas/metabolismo , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
Editing of plastid RNAs proceeds by C-to-U, in hornwort species also by extensive U-to-C, transitions, which predominantly lead to the restoration of codons for structurally and/or functionally important, conserved amino acid residues. So far, only one instance of editing outside coding regions has been reported - in the psbL/ psbF intergenic region of Ginkgo biloba. This site was proposed to have no functional importance. Here we present an evaluation of an editing site in the ndhI/ ndhG intergenic region in a related group of monocot plants. Efficient editing of this site, as well as the phylogenetic conservation of the resulting uridine residue, point at an important role for the sequence restored by editing. Two potential functions can be envisaged. (1) RNA secondary structure predictions suggest that the C-to-U conversion at this site can lead to a modified stem/loop structure of the ndhG 5' UTR, which could influence ndhG expression. (2) Alternatively, editing of the ndhI/ ndhG intergenic region may tag a so far unidentified small (12-codon) ORF, and lead to the restoration of a conserved phenylalanine codon. A screen with specific antibodies elicited against the putative peptide failed to detect such a peptide in chloroplast fractions. However, this failure may be attributable to its low and/or development-specific expression.
Assuntos
Magnoliopsida/genética , Magnoliopsida/metabolismo , Edição de RNA , RNA de Plantas/genética , RNA de Plantas/metabolismo , Sequência de Aminoácidos , Sequência de Bases , DNA de Plantas/genética , Genes , Genes de Plantas , Dados de Sequência Molecular , NADH Desidrogenase/genética , Conformação de Ácido Nucleico , Plastídeos/genética , RNA de Plantas/química , Fases de Leitura , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido NucleicoRESUMO
Acorus calamus, or sweet flag, is a semiaquatic plant of uncertain taxonomic position. Molecular phylogenetic analysis using plastid rbcL sequences have suggested that Acorus calamus might be the most ancient surviving representative of the ancestral monocotyledonous plants. In order to provide molecular and phylogenetic data for the mitochondrial genetic system of Acorus, we have determined the structure of a mitochondrial locus, the cytochrome oxidase subunit II gene cox2. The Acorus cox2 gene harbors an unusually small group II intron, the smallest plant mitochondrial intron known to date. The transcript undergoes C-to-U RNA editing at eight sites. One of these sites is likely to play a dual functional role in both intron splicing and protein function. The 3' end of the mature transcript folds into a characteristic stem-loop structure that is presumably required for mitochondrial mRNA stability. Phylogenetic analysis of the cox2 sequence data, as well as the unusual intron structure, all support an evolutionarily isolated position for Acorus calamus.