Recent degeneration of an old duplicated flowering time gene in Brassica nigra

Birth-and-Death Evolution of the Fatty Acyl-CoA Reductase (FAR) Gene Family and Diversification of Cuticular Hydrocarbon Synthesis in Drosophila

The birth-and-death evolutionary model proposes that some members of a multigene family are phylogenetically stable and persist as a single copy over time, whereas other members are phylogenetically unstable and undergo frequent duplication and loss. Functional studies suggest that stable genes are likely to encode essential functions, whereas rapidly evolving genes reflect phenotypic differences in traits that diverge rapidly among species. One such class of rapidly diverging traits are insect cuticular hydrocarbons (CHCs), which play dual roles in chemical communications as short-range recognition pheromones as well as protecting the insect from desiccation. Insect CHCs diverge rapidly between related species leading to ecological adaptation and/or reproductive isolation. Because the CHC and essential fatty acid biosynthetic pathways share common genes, we hypothesized that genes involved in the synthesis of CHCs would be evolutionary unstable, whereas those involved in fatty acid-associated essential functions would be evolutionary stable. To test this hypothesis, we investigated the evolutionary history of the fatty acyl-CoA reductases (FARs) gene family that encodes enzymes in CHC synthesis. We compiled a unique data set of 200 FAR proteins across 12 Drosophila species. We uncovered a broad diversity in FAR content which is generated by gene duplications, subsequent gene losses, and alternative splicing. We also show that FARs expressed in oenocytes and presumably involved in CHC synthesis are more unstable than FARs from other tissues. Taken together, our study provides empirical evidence that a comparative approach investigating the birth-and-death evolution of gene families can identify candidate genes involved in rapidly diverging traits between species.

The recent evolution of a pseudogene: diversity and divergence of a mitochondria-localized small heat shock protein inArabidopsis thaliana

In this study we examined the evolution of the genes for three organelle-localized small heat shock proteins in Arabidopsis thaliana : the chloroplast-localized (CP) protein HSP21 and two mitochondria-localized (MT) proteins, HSP23.5 and HSP23.6. We found that the CP protein and one of the MT proteins, HSP23.6, are evolving under purifying selection to maintain function. In contrast, the gene for HSP23.5, the other MT protein, is highly variable within A. thaliana, and in some accessions or ecotypes this gene may be a pseudogene. HSP23.5 and HSP23.6 are related via a segmental duplication event, and the presence of orthologs of each gene in other species within the Brassicaceae indicates that the duplication generating HSP23.5 and HSP23.6 may have occurred as much as 20 million years ago. This is considerably longer than the 4 million year half-life of gene duplicates (functional genes as well as pseudogenes) reported by some studies. Our results are consistent with the prediction that after gene duplication one gene duplicate can be maintained for some time under relaxed selection while it accumulates random mutations. By capturing a pseudogene in the making our study provides important information on how pseudogenes are formed.