Evolutionary Consequences

Evolution of plant species is the outcome of numerous processes including gene duplication and loss, whole genome duplication, fluctuation in ploidy level, ret-rotransposon activity, and genome rearrangements (Goff et al. 2002; Yu et al. 2002; Wicker et al. 2003; Kellogg and Bennetzen 2004; Caicedo and Purugganan 2005; Ming et al. 2008). Trends in genome size fluctuate substantially in different plant lineages. Expansion of the sorghum genome relative to rice occurred largely in heterochromatic regions comprised largely of LTR-retrotransposons (Paterson et al. 2009). A total of 58% of the sorghum genome is comprised of pericentromeric heterochromatin versus 15% of rice. The turnover of cereal genomes retrotranspo-sons has been rapid in cereal crops (Swigonova et al. 2005).

Through comparative sequence analysis, wide range in genome size variation in Gossypium genome has largely been attributed to differential proliferation of dispersed repetitive elements (Zhao et al. 1998; Hawkins et al. 2006) which was detected in heterochromatic regions located between highly conserved, euchromatic gene islands (Grover et al. 2004; Hawkins et al. 2006). Genome size fluctuation may also be affected by other mechanisms including variation in intron length, expansion/contraction of tandem repeats, illegitimate recombination, indel bias, and unequal intrastrand homologous recombination (Petrov and Wendel 2006). It was also speculated that smaller genomes carry smaller introns (Deutsch and Long 1999; Vinogradov 1999); however, such a correlation was not observed in the genome Gossypium (Wendel et al. 2002; Grover et al. 2004).

0 0

Post a comment