03.2020 | THE SCIENTIST 47KIM AAEN, NATUREEYES; ANDREAS BATTENBERG/TUM
PATHOGEN PROTECTION: Weaver ants (Oecophylla smaragdina) and other
ant species may protect their plant hosts from infectious bacteria and fungi.ECOLOGY & ENVIRONMENTAnts on Plants
THE PAPER
J. Offenberg, C. Damgaard, “Ants suppressing plant pathogens: a
review,” Oikos, doi:10.1111/oik.06744, 2019.Some ants produce natural antibiotic chemicals to defend themselves
against fungi and bacteria. Ecologist Joachim Offenberg of Aarhus
University in Denmark wondered what effect these compounds
had on the health of the plants the ants called home. “We had this
thought that if ants produce antibiotics, maybe these antibiotics
could have an effect... on the diseases of the plants they walk on,”
he tells The Scientist.
In a review of studies investigating the effect of ants on plant
pathogens, he and fellow Aarhus ecologist Christian Damgaard found
that, out of 30 plant species that were commonly inhabited by some
kind of ant, 18 showed a decrease in the effects of pathogens. These
included reduced bacterial load and increased germination rates
enjoyed by plants inhabited by ants compared with plants of the same
species that did not host ants.
Data have long confirmed that ants provide protection to
their botanical hosts by eating pests, says Andreas Schramm, a
microbiologist at Aarhus University who was not involved with the
study. “The chemical defense of plants is really another direction
that the authors quite convincingly put out here,” he says. Overall,
Offenberg and Damgaard estimated that the effects of ants’ antibiotics
were comparable to the benefits plants receive from the insects’
consumption of herbivorous pests.
Six of the plant species had increased pathogen incidence with
ants, however, and six either had no significant difference between
groups or insufficient data. Offenberg notes that a plant that hosts
ants may already have a major infection that can’t be controlled with
ant-produced antimicrobial compounds. Moreover, the insects can
inadvertently disperse pathogens: fungal spores, for example, can cling
to their legs.
The paper is “more than a review,” says Schramm. “It’s actually a
really good analysis that points especially to the holes in our knowledge.”
—Emily MakowskiPHENOTYPES: Researchers examined the roots of mutant Arabidopsis
thaliana seedlings grown in agar for clues about genes’ functions.CELL & MOLECULAR BIOLOGYSmoke Signals
THE PAPER
J.A. Villaécija-Aguilar et al., “SMAX1/SMXL2 regulate root and
root hair development downstream of KAI2-mediated signalling in
Arabidopsis,” PLOS Genet, 15:e1008327, 2019.Beginning with her PhD work more than a decade ago, Caroline
Gutjahr has investigated the effects of karrikins, compounds that
are generated when plants burn and that influence germination
of fire-following plants. Last year, her group at the Technical
University of Munich grew seedlings of an Arabidopsis thaliana
mutant with a karrikin receptor knocked out. “The first thing we
saw is that the roots are not growing straight down, but they’re
slanting, so it looked very weird,” she says. The hairs on the roots,
which are crucial to nutrient and water absorption in young plants,
were also shorter and sparser than those on wildtype Arabidopsis.
With collaborators at the University of Leeds, Gutjahr’s group
grew mutant seedlings missing other components of karrikin
signaling, as well as plants lacking elements of a related pathway
triggered by plant hormones known as strigolactones. In previous
studies, other research groups had linked strigolactones to root
development aberrations. In the new study, the root phenotypes
of the mutants revealed that most of the defects were actually
due to disruptions in the karrikin pathway. One reason for the
mistaken conclusion is that both karrikin and strigolactone
signaling work through a protein called MAX2, the gene for
which was mutated in some previous studies, the paper’s
authors write.
Because it offers insight into the molecular mechanisms of
a puzzling root phenotype, the study is “really useful... for the
root field and also for the strigolactone field,” says Yanxia Zhang,
a plant biologist at Wageningen University in the Netherlands
who was not involved in the work. The results also show that the
strigolactone and karrikin receptors lack specificity. That finding
suggests they may also be activated by other compounds, she
adds, and warrants further investigation.
—Shawna Williams