Solanaceae Tomato Potato Eggplant Peppers

The members of the Solanaceae family especially tobacco (Nicotiana tabacum), potato (S. tuberosum) and eggplant (S. melongena) have relatively few rearrangements in their genomes. Low-resolution comparative mapping suggests that disease resistance loci (R) are well conserved in the Solanaceae (Grube et al. 2000; Pan et al. 2000) while evolving much faster in the crucifer and grass genomes (Gale and Devos 1998; Leister et al. 1998; Paterson et al. 2000). The genomic region in the long arm of tomato chromosome 11 has been conserved across many members of the Solanaceae, and has been investigated for isolation of new R genes using comparative genomic approaches (El-Kharbotly et al. 1994, 1996; Lefebvre et al. 1995; Ori et al. 1997; Simons et al. 1998; Hanson et al. 2000). The R3a gene (confers race-specific resistance to the late blight pathogen) was isolated from potato which corresponds with the I2 complex locus in tomato. After the divergence of potato and tomato, the R3 locus has gone through a significant expansion in number of genes and functional diversification while keeping intact the flanking co-linearity (Huang et al. 2004, 2005).

In multiple investigations, different degrees of restructuring within and across plant taxa was reported (Lagercrantz and Lydiate 1996; Livingstone et al. 1999; Ku et al. 2000; Thorup et al. 2000; Fulton et al. 2002; Salse et al. 2002; Bennetzen and Ma 2003; Nishiyama et al. 2003). For example, within Solanaceae, the genomes of potato and tomato differ only by five paracentric inversions (Bonierbale et al. 1988; Tanksley et al. 1992; Doganlar et al. 2002a), suggesting a high propensity for intrachromosomal rearrangements. Around 30 chromosomal breaks distinguish the genomes of tomato and pepper (Prince et al. 1993; Livingstone et al. 1999), a relatively high degree of chromosomal rearrangements. Genomic comparison with other plant taxa have shown a syntenic relationship of 90 blocks covering 41% of the potato genetic map with 50% of the Arabidopsis physical map, indicated that ancient intra- and interchromosomal duplications has played a role in potato genome evolution (Gebhardt et al. 2003).

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