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NEWS
The Evolution of Beer
From Austrian monks to American craft brewers, beer geeks
are everywhere. But making a good beer not only depends on
the best ingredients, but also the best yeast.
The beer world is divided into ales and lagers. Lager yeasts
are hybrid strains, made of two different yeast species,
Saccharomyces cerevisiae and S. eubayanus (discovered in
2011).
In a new study in the journal Molecular Biology and
Evolution, graduate student Emily Clare Baker, corresponding
author Baker et al. (2015) studied the complete genomes of
both parental yeast species contributing to lager beer.
They proved that two independent origin events occurred
for S. cerevisiae and S. eubanyus hybrids found in lager beers.
Lager beer making has placed yeast on similar evolutionary
trajectories multiple times.
“Lager yeasts did not just originate once. This unlikely marriage between two species, genetically as different from one
another as humans and birds, happened at least twice.
Although these hybrids were different from the start, they
also changed in some predictable ways during their domestication,” said Hittinger.
The blueprint of the powerhouses of the yeast cell, called
mitochondrial genome sequences, proved that S. eubayanus
served as the main donor of mtDNA for lager yeasts of
Frohberg lineage. They also found that both the Saaz and
Frohberg yeasts contained S. cerevisiae (99.57% identical to
strain S288c) and S. eubayanus (99.55% identical to FM1318)
genomes. They also compared the mitochondrial genomes
and found S. eubayanus to be 6.6 kb smaller than Frohberg
yeast and 21.8 kb smaller than S. cerevisiae.
In addition, since being adapted for beer making, the S.
eubayanus genomes have experienced increased rates of evolution, including in some genes involved in metabolism.
Some metabolism genes, especially those involved in fermentation and sugar metabolism, may have been shaped by
domestication in brewing. In particular, the authors suggest
that many evolutionary changes may have reduced the function of the Adr1 protein, which activates an alcohol dehydrogenase that consumes alcohol, rather than producing it.
The findings have now clarified the origins of the major
lineages of the hybrid yeasts used to brew lagers, and will
provide a roadmap for future research in the domestication
of lager yeasts.
Reference
Baker EC, Wang B, Bellora N, Peris D, Hulfachor AB, Koshalek AJ, Adams
M, Libkind D, Hittinger CT. 2015. The genome sequence of
Saccharomyces eubayanus and the domestication of lager-brewing
yeasts. Mol Biol Evol. 32(11)):2818–2831.
Joseph Caspermeyer*,1
1
MBE Press Office
*Corresponding author: E-mail: [email protected].
doi:10.1093/molbev/msv229
Advance Access publication November 26, 2015
From slight sparrows to preening peacocks to soaring falcons,
birds have long been known to possess distinct abilities in
their sense of smell, but little has been known about the
evolution of olfaction.
Now, a large comparative genomic study of the olfactory
genes tied to a bird’s sense of smell has revealed important
differences that correlate with their ecological niches and
specific behaviors.
Khan et al. (2015) analyzed olfactory receptor genes (OR
gene families) from 48 ecologically diverse bird and two reptilian genomes. In vertebrates, ORs are considered to be one
the largest multigene families, ranging from a single gene in
elephant sharks to more than 1,000 genes in mammals.
The study provides evidence that specific OR genes are
used not only to detect a range of chemicals governing a
bird’s ability to smell, but that the dominant bird behavior
such as those found in birds of prey or aquatic birds—was
often mirrored by the genetic diversity of their OR gene
families.
In the study, drastic expansion of specific OR’s gene families, such as OR51 and OR52, were seen in sea turtles and
aquatic birds to detect water-loving (hydrophilic) compounds. In contrast, the expansion of OR14 was found in
the birds that could smell volatile compounds (terrestrial
birds).
Overall, OR families 2, 13, 51, and 52 were more common
in aquatic birds and 6 and 10 were associated with vocal
learners. Birds of prey had a comparatively high percentage
of OR families 5, 8, and 9. These were also the largest OR
families observed in alligators, which like birds of prey, depend
on hunting or scavenging for food, which also suggests that
these genes are needed for adaptation in carnivores.
Finally, the research team related the genetic differences to
bird anatomy, and the size of the olfactory bulb, the main
ß The Author 2015/2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please
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Mol. Biol. Evol. 33(1):295–298
295
NEWS
Evolutionary Study of Birds’ Sense of Smell Reveals Important
Clues for Behavior and Adaptation
neurological structure involved in smell. The relative size of
the olfactory bulb in birds was also found to correlate with
ecological adaptations, including habitat association (e.g.,
water birds), type of nesting strategy, and diet. For example,
birds of prey, including vultures and seabirds, hunt and recognize food by smell, and have relatively large olfactory bulbs,
whereas song birds that rely more on cognitive abilities helpful in tool making, vocal learning, and feeding innovations
have reduced olfactory bulb sizes.
Overall, the role of ecological adaptation in shaping the OR
gene families has been found to be consistent in both birds
and mammals, indicating the importance of a sense of smell
to an animal’s fitness, survival, and niche.
Reference
Khan I, Yang Z, Maldonado E, Li C, Zhang G, Gilbert MTP, Jarvis ED,
O’Brien SJ, Johnson WE, Antunes A. 2015. Olfactory receptor subgenomes linked with broad ecological adaptations in Sauropsida.
Mol Biol Evol. 32(11)):2832–2843.
Joseph Caspermeyer*,1
1
MBE Press Office
*Corresponding author: E-mail: [email protected].
doi:10.1093/molbev/msv230
Advance Access publication November 18, 2015
Of Skin and Teeth: Identifying Key Differences in Asians
Marques et al. (2016) have found key differences in a suite of
genes important for skin and bone development that may
have bestowed specific advantages among Asians.
They focused on the human kallikrein cluster (KLK), a suite
of fifteen genes clustered on the long arm of chromosome 19
that play a key role in human adaptation and reproductive
biology. The genes function as molecular scissors called serine
proteases, which target and clip other proteins involved in
semen function, teeth development, skin, and blood pressure
maintenance, and even cancer.
The team undertook a large study to identify 1,419 DNA
differences in the KLK genomic cluster among Eastern Asian
(Han Chinese and Japanese), African and European populations by using new DNA data from the 1000 Genomes
project.
The most striking differences were narrowed down to two
regions near the KLK4 gene, which were found to severely
hamper the activity of KLK4 only in Asian populations.
This may contribute to dental traits typically found in
Asians and important in controlling skin conditions like eczema, which is much more prevalent in northern Europe than
in Asia.
“We further predict many effects related to male biology
and other physiological functions with possible outcomes in
human complex diseases, said Seixas. “KLK4 is a pervasive
protease, expressed in a wide range of tissues, and frequently
over-expressed in prostate, ovarian, and breast cancers, where
it is thought to play a role in tumor progression and
metastasis.
We are only at the tip of the iceberg, but one very exciting
possibility is that the same differences may confer a selective
advantage to offering a reduced risk to several cancer types
with lower incidences in East-Asia.”
Reference
Marques PI, Fonseca F, Sousa T, Santos P, Camilo V, Ferreira Z, Quesada
V, Seixas S. 2016. Adaptive evolution favoring KLK4 downregulation
in East-Asians. Mol Biol Evol. 33:93–108.
Joseph Caspermeyer*,1
1
MBE Press Office
*Corresponding author: E-mail: [email protected].
doi:10.1093/molbev/msv231
Advance Access publication November 24, 2015
Knee-Deep in Spider Leg Evolution
Turetzek et al. (2016) have identified the driving force behind the evolution of a leg novelty first found in spiders:
knees.
With eight hairy legs and seven joints on each—that’s a lot
of knees to account for and coordinate just for a spider to
take a single step. Prpic’s research team honed in on a gene
called dachshund (dac). The gene was first discovered in fruit
flies, and humorously named for the missing leg segments
and shortened legs that result from dac mutant flies.
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But arachnids are different than flies and other
arthropods, possessing a second dac gene. And the dac2
gene is made only in the kneecap, or patella, during spider
development.
When the research group used RNA interference experiments to specifically deactivate dac2, the kneecap
fuses to the tibia into a single leg segment. The force
behind knees first appearing on the spider evolutionary
scene was a result of ancient gene duplication in the