437 research outputs found
Molecular mechanism of protrusion formation during cell-to-cell spread of Listeria
The bacterial pathogen Listeria monocytogenes spreads within human tissues using a motility
process dependent on the host actin cytoskeleton. Cell-to-cell spread involves the ability of
motile bacteria to remodel the host plasma membrane into protrusions, which are internalized
by neighboring cells. Recent results indicate that formation of Listeria protrusions in
polarized human cells involves bacterial antagonism of a host signaling pathway comprised
of the scaffolding protein Tuba and its effectors N-WASP and Cdc42. These three human
proteins form a complex that generates tension at apical cell junctions. Listeria relieves this
tension and facilitates protrusion formation by secreting a protein called InlC. InlC interacts
with a Src Homology 3 (SH3) domain in Tuba, thereby displacing N-WASP from this
domain. Interaction of InlC with Tuba is needed for efficient Listeria spread in cultured
human cells and infected animals. Recent structural data has elucidated the mechanistic details of InlC/Tuba interaction, revealing that InlC and N-WASP compete for partly
overlapping binding surfaces in the Tuba SH3 domain. InlC binds this domain with higher
affinity than N-WASP, explaining how InlC is able to disrupt Tuba/N-WASP complexes.Grants from the National Institutes of Health (R01AI085072) and the Marsden Fund of the Royal Society of New Zealand (UOO1003), Medical Research Council of South Africa, the National Research Foundation of South Africa and previously by the Helmholtz Centre for Infection Research, Braunschweig, Germany.http://www.frontiersin.org/Cellular_and_Infection_Microbiologyhb201
Re‐examining the evidence for the mother tree hypothesis – resource sharing among trees via ectomycorrhizal networks
Seminal scientific papers positing that mycorrhizal fungal networks can distribute carbon (C) among plants have stimulated a popular narrative that overstory trees, or 'mother trees', support the growth of seedlings in this way. This narrative has far-reaching implications for our understanding of forest ecology and has been controversial in the scientific community. We review the current understanding of ectomycorrhizal C metabolism and observations on forest regeneration that make the mother tree narrative debatable. We then re-examine data and conclusions from publications that underlie the mother tree hypothesis. Isotopic labeling methods are uniquely suited for studying element fluxes through ecosystems, but the complexity of mycorrhizal symbiosis, low detection limits, and small carbon discrimination in biological processes can cause researchers to make important inferences based on miniscule shifts in isotopic abundance, which can be misleading. We conclude that evidence of a significant net C transfer via common mycorrhizal networks that benefits the recipients is still lacking. Furthermore, a role for fungi as a C pipeline between trees is difficult to reconcile with any adaptive advantages for the fungi. Finally, the hypothesis is neither supported by boreal forest regeneration patterns nor consistent with the understanding of physiological mechanisms controlling mycorrhizal symbiosis
Selected reactive oxygen species and antioxidant enzymes in common bean after Pseudomonas syringae pv. phaseolicola and Botrytis cinerea infection
Phaseolus vulgaris cv. Korona plants were
inoculated with the bacteria Pseudomonas syringae pv.
phaseolicola (Psp), necrotrophic fungus Botrytis cinerea
(Bc) or with both pathogens sequentially. The aim of the
experiment was to determine how plants cope with multiple
infection with pathogens having different attack strategy.
Possible suppression of the non-specific infection with
the necrotrophic fungus Bc by earlier Psp inoculation was
examined. Concentration of reactive oxygen species
(ROS), such as superoxide anion (O2
-) and H2O2 and
activities of antioxidant enzymes such as superoxide dismutase
(SOD), catalase (CAT) and peroxidase (POD) were
determined 6, 12, 24 and 48 h after inoculation. The
measurements were done for ROS cytosolic fraction and
enzymatic cytosolic or apoplastic fraction. Infection with
Psp caused significant increase in ROS levels since the
beginning of experiment. Activity of the apoplastic
enzymes also increased remarkably at the beginning of
experiment in contrast to the cytosolic ones. Cytosolic
SOD and guaiacol peroxidase (GPOD) activities achieved
the maximum values 48 h after treatment. Additional forms
of the examined enzymes after specific Psp infection were
identified; however, they were not present after single Bc
inoculation. Subsequent Bc infection resulted only in
changes of H2O2 and SOD that occurred to be especially
important during plant–pathogen interaction. Cultivar Korona
of common bean is considered to be resistant to Psp and mobilises its system upon infection with these bacteria.
We put forward a hypothesis that the extent of defence
reaction was so great that subsequent infection did not
trigger significant additional response
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