Most of genes contained in a genome have been shown to exist in forms of
families; however, little is known about their variation and evolution during the course
of genome evolution. The present study shows that the numbers of the genes of the
NBS-LRR-encoding gene family vary extremely significantly among different lines or
cultivars of a species and among related species from the same genus. This suggests
that plant genetics and evolution depend on not only gene sequence variation, but also
the number of genes in multigene families. This study has further revealed that the
variation of number of genes in the gene family in the Gossypium species is affected
significantly not only by genome size variation, polyploidization and natural selection,
but also by domestication/breeding. There is a positive correlation (P less than or equal to 0.05) between
genome size and number of genes in the family, suggesting that species with larger
genomes tend to have more NBS-LRR-encoding genes. It was observed that natural
polyploids have significantly larger numbers of genes in the family and larger genomes
than the artificial polyploids of their putative diploid ancestors. This indicates that
polyploidization, perhaps post-polyploidization as well, either led to the loss of the
genes in a gene family or slowed the process of gene number increase after polyploidization. It was shown that cultivated cottons have significantly more NBSLRR-
encoding genes than wild species at both diploid and polyploidy levels. This
result indicates that plant breeding likely allows accumulation of NBS-LRR-encoding
genes that potentially provide resistance to pathogens. Therefore, plant breeders have
selected not only for favorable alleles and favorable allele combinations, but also for
the number of genes. Finally, difference (P less than or equal to 0.001) was found in number of genes in
the NBS-LRR-encoding gene family among the species native to different geographical
regions, suggesting that natural selection has played an important role in the variation
in number of genes in the NBS-LRR-encoding gene family. The gene members that are
favorable for fitness at the time are selected and accumulated in the genomes, but those
that are not favorable for fitness at the time are lost in natural selection.
As this is the first study in the field, further studies remain. These include, but not
limited to, the universality of the findings in plants and animals, the universality of the
findings in different gene families, genetics of the gene family size variation,
relationship between the gene family size variation and phenotypic variation, gene
family size variation and breeding, etc. Nevertheless, the findings obtained from this
study are sufficient to shed light on many fundamental questions in biology, diversity
and complexity of plants and animals.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-669 |
| Date | 2009 May 1900 |
| Creators | Wu, Yen Hsuan |
| Contributors | Zhang, Hongbin, Zhang, Hongbin |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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