The comparison of the genes and their introns revealed a unique example that may shed some light on these evolutionary processes: compared with its sister species, one of the studied genes of M. graminicola acquired an intron only recently and this intron then rapidly increased in frequency to near fixation. Why a new intron could so rapidly become fixed in this gene in M. graminicola is a mystery. "Maybe individuals carrying this intron have a fitness advantage compared to individuals without the intron," Croll muses, "this is our first evidence that natural selection may play a role in intron fixation".
Effects on fitness remain unclear
Researcher can still only speculate whether introns offer any general advantages to eukaryotes. Many more experiments will be needed to confirm or discard current ideas regarding the role of introns in genome evolution. "For example, do introns affect the fitness of a species, does the loss or gain of an intron increase fitness, decrease fitness or have neutral consequences for an individual or a species? We simply do not know", says the ETH professor.
As a result of their comparison across several fungal genomes and individual genes, the ETH Zurich researchers also found the first concrete examples illustrating that introns can multiply and insert themselves elsewhere in the genome. The researchers were able to identify whole families of closely related introns, and then determine the frequency with which a particular intron family was present in the genome.
Analysing human introns next?
The researchers are convinced that their work will lead to a better understanding of intron evolution for all eukaryotes. Following their example, one can perform similar gene or genome analysis in other organisms, especially due to the rapid development of ever faster and cheaper sequencing technologies. Fungi have relatively small genome
|Contact: Bruce McDonald|
ETH Zurich/Swiss Federal Institute of Technology