Abstract
Gypsy group retrotransposons in the Egyptian cotton, Gossypium barbadense, was examined by phylogenetic and molecular evolutionary analyses. DNA sequences ofgypsy group retrotransposons in two G. barbadense cultivars revealed that these sequences are heterogeneous and represent two distinct families. Sequence variation between these families seems to preserve coding information of the reverse transcriptase domain. The high ratio of synonymous to nonsynonymous changes indicates that the reverse transcriptase domain of these families is evolving under purifying selection. Our phylogenetic analysis revealed that the closest relatives of cotton retroelements are found in other plants gypsy group retrotransposons. Cotton retroelements-encoded transcripts were detected in their related respective young seedlings using RNA slot-blot hybridization, suggesting their transcriptional activity. The wide distribution of gypsygroup retrotransposons and the detection of their encoded transcripts illustrate their active role in the Gossypium genome. Key words: Evolution, Gossypium, gypsy, retrotransposons, reverse transcriptase, substitution rates, transcription.
Highlights
Gossypium L. contains 50 species whose phylogenetic relationships have been explored using multiple molecular data sets
The genus Gossypium is a facile system for investigating the genomic organization and evolution of repetitive DNA sequences that become newly united in a common nucleus (Zhao et al, 1995)
As part of a long-term program to understand the organization and evolution of the cotton genome, we describe the phylogenetic and molecular evolutionary analyses of gypsy group retrotransposons in the Egyptian cotton Gossypium barbadense
Summary
Gossypium L. contains 50 species whose phylogenetic relationships have been explored using multiple molecular data sets (reviewed in Wendel and Cronn, 2003). The five natural polyploids in the genus are believed to have generated from a single polypliodization event 1.5 million years ago (MYA) (Senchina et al, 2003) They all represent the AD genome tetraploids combining an A-genome donated by the maternal diploid parent at the time of polyploidy formation and a D-genome from the pollen parent (Wendel and Cronn, 2003). Cloning and characterization of the major repetitive DNA in the tetraploid (AD) cotton revealed that most dispersed repeat families are largely restricted to the A-genome diploid ancestor and are absent from the D-genome (Zhao et al, 1998). The current report complements our recent analysis of the characterization and distribution of gypsy and copia group retrotransposons in the Egyptian cotton (Abdel Ghany and Zaki, 2002, 2003, Zaki and Abdel Ghany, 2003)
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