Ginormous Genome

Researchers find organisms with huge genomes with high mutation rates, overturning a common expectation in evolutionary biology.

By | May 1, 2012

image: Ginormous Genome MEGA MITOCHONDRIA: Researchers find that two flowering plants in the Silene genus (above) have comparatively enormous genomes in their mitochondria, an organelle with a high mutation rate.Yale University

MEGA MITOCHONDRIA: Researchers find that two flowering plants in the Silene genus (above) have comparatively enormous genomes in their mitochondria, an organelle with a high mutation rate. YALE UNIVERSITY

EDITOR'S CHOICE IN PLANT BIOLOGY

The paper

D.B. Sloan et al., “Rapid evolution of enormous, multichromosomal genomes in flowering plant mitochondria with exceptionally high mutation rates,” PLoS Biology, 10 (1) e:1001241, 2012.

The finding

Based on high mutation rates seen in small mitochondrial genomes, researchers hypothesized that elevated mutation rates would result in smaller streamlined genomes with less noncoding DNA. But Daniel Sloan at the University of Virginia found that mutation rates aren’t always linked to size. Sloan identified two enormous, rapidly mutating plant mitochondrial genomes, suggesting that other mechanisms may regulate genome size.

The paradigm

Mutations within coding regions are risky, but adding more noncoding DNA compounds the risk. Mutations in noncoding sequences can create false start-sequences and other nonsense code that can impede the normal function of the cell as much as mutations in proteins can.

The flowers

Sloan sequenced the mitochondrial genomes of two carnation species with unexpectedly high mutation rates, and discovered two behemoths at 6.7 and 11.3 Mb , more than ten times the size of the largest known plant mitochondrial genomes.

The complication

Sloan’s work doesn’t completely subvert the old paradigm, however, says Benoit Nabholz of Université Montpellier II in France. Though sequences between the genes expanded, the average intron lengths decreased, hinting at a more complex relationship between mutation rate and genome size.

 

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Comments

Avatar of: Edward R. Mikol

Edward R. Mikol

Posts: 1457

May 2, 2012

Wouldn't a higher mutation rate be an evolutionary advantage?

Avatar of: Robin Craig

Robin Craig

Posts: 1457

May 2, 2012

 Depends on how stable the niche is. Higher mutation rates have been found to be beneficial in cases of low fitness relative to the current environment but the better adapted an organism is to its environment, the more trouble mutations cause. In other words it's a trade off between the probability of damaging the good stuff you have and evolutionary potential in adapting to new things.

Avatar of:

Posts: 0

May 2, 2012

Wouldn't a higher mutation rate be an evolutionary advantage?

Avatar of:

Posts: 0

May 2, 2012

 Depends on how stable the niche is. Higher mutation rates have been found to be beneficial in cases of low fitness relative to the current environment but the better adapted an organism is to its environment, the more trouble mutations cause. In other words it's a trade off between the probability of damaging the good stuff you have and evolutionary potential in adapting to new things.

Avatar of:

Posts: 0

May 14, 2012

If one looks at mitochondrial genomes across the eukaryotic diversity, these findings fit very well with the current paradigm of Mt genomes, which is "anything goes"

Avatar of:

Posts: 0

May 14, 2012

Given the symbiotic relationship between mitochondria and their host cells, and given that in different lineages the relationship between the nuclear genome and the MT genome may differ, an attempt to infer general evolutionary principles from studies of MT genomes alone seems, well, problematic.

Avatar of: Claudio Slamovits

Claudio Slamovits

Posts: 1457

May 14, 2012

If one looks at mitochondrial genomes across the eukaryotic diversity, these findings fit very well with the current paradigm of Mt genomes, which is "anything goes"

Avatar of: RJR8222

RJR8222

Posts: 4

May 14, 2012

Given the symbiotic relationship between mitochondria and their host cells, and given that in different lineages the relationship between the nuclear genome and the MT genome may differ, an attempt to infer general evolutionary principles from studies of MT genomes alone seems, well, problematic.

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