Browsing by Subject "signaling"

Now showing 1 - 4 of 4
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    Complex signals and perceiver behavior
    (2015-12) Rubi, Tricia
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    Ecology of interspecies signaling among Streptomyces and its relationship to pathogen suppression
    (2013-05) Vaz Jauri, Patricia
    Interspecies signaling may be defined as the induced change in phenotype of one species by another that is not due to the metabolism of the signal. Although suggested to be a relatively widespread phenomenon, the role of signaling in natural soil communities has not been thoroughly studied. Within Streptomyces communities in soil, understanding the impacts of interspecies signaling on species interactions, and especially on nutrient competition and antagonism, may be key to effective Streptomyces-based suppression of plant pathogens. I evaluated the frequency of signaling interactions and their effect on inhibitory phenotypes of Streptomyces isolated from natural prairies. Signaling among Streptomyces was frequent, and observed in 35% of all interactions. Isolates from the same location in soil were more likely to signal one another than isolates from different locations, suggesting local selection for signaling interactions. Signaling was similarly more frequent between isolates that had similar nutrient use profiles. Finally, closely-related isolates were more likely to increase inhibition towards one another via signaling than distantly-related isolates. In chapter 2, subinhibitory concentrations of antibiotics were studied as signals, specifically in relation to their capacities to shift nutrient use among Streptomyces. We found that some antibiotics altered nutrient use by Streptomyces in ways that could reduce nutrient competition among isolates. Finally, pathogen suppression and signaling were evaluated in soils with different cropping histories. Pathogen suppression by Streptomyces varied significantly among soils, and suppressive activity was positively correlated with bacterial density. Among Streptomyces from these plots, shifts in inhibitory phenotypes in response to signaling by another isolate were very frequent (~ 50% of all interactions). Overall, signaling in Streptomyces is frequent and varies with spatial origin, nutrient overlap, antagonistic phenotype, and genetic relatedness among isolates, as well as soil cropping history. Moreover, some antibiotics have the potential to act as signals that can significantly alter nutrient competition among Streptomyces. Variation in signaling has significant potential to mediate pathogen suppression in soil communities.
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    The economics of animal communication: theory and experiments integrating receiver choice and strategic signal reliability
    (2015-12) Polnaszek, Timothy
    This research centers on two themes fundamental to communication, signal reliability and receiver tolerance of imperfect reliability (abbreviated as receiver tolerance). Focus on signal reliability tends to dominate research on signaler-receiver interactions, but represents only half of the signaling dyad. Understanding why signals are reliable and why receivers follow imperfect reliability are equally important; I argue the combination of reliability and receiver tolerance to ultimately determines the form and stability of signaler-receiver interactions. To explore these themes, I first developed a model of signaling interactions that combines aspects of models of receiver choice and signal reliability. The results highlight the co-importance of receiver tolerance and reliability enforcement mechanisms (such as signal cost). To experimentally test the model predictions, I developed a novel laboratory signaling game that allows control over theoretically important variables (such as the level of conflict between the signaler and receiver). The game placed blue jay subjects (Cyanocitta cristata) in a signal-response game played for food rewards. A series of these signaling-game experiments demonstrate the effects of signal cost on signal reliability (or honesty) and show the extent to which uncertainty in the environment generates receiver tolerance. Signal cost is an important topic in signaling theory, but lacks direct empirical support. I show that high signal cost does increase honesty under conditions of conflict, but also that cost is unnecessary in mutualistic conditions. I also show that receiver tolerance increases when environments are uncertain (to the point that receivers are gullible), and that signalers are sensitive to the level of receiver tolerance – exploiting tolerance when signaler and receiver interests conflict. Taken together, these models and experiments establish the value of considering both signal reliability and receiver tolerance.
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    Positive And Negative Regulation Of Defense Responses Against Pseudomonas Syringae In Arabidopsis
    (2014-03) Sreekanta, Suma
    Immune signaling in plants involves both positive and negative regulators. Maintaining a balance between growth and defense responses is important because there is a fitness cost to the plants if immune responses are left unchecked. Suppression of immune responses in the absence of pathogens as well as after the threat has passed is critical in maintaining such a balance between growth and defense responses. Upon pathogen perception, the positive regulators counter the immune repression to induce defense responses. We investigated the roles of two genes, CBP60a and PCRK1 in the regulation of defense responses against Pseudomonas syringae pathogen in the model system Arabidopsis thaliana . CBP60a is a negative regulator of immune responses. We showed that CBP60a is a CaM binding protein and that CaM binding is important for its function in transducing defense signals. Mutants of CBP60a were more resistant to Pseudomonas syringae infection suggesting that CBP60a was a negative regulator of defense responses. We found that CBP60a functions in repressing immune signaling under conditions where the plants are not challenged by a pathogen. We also investigated the role of a putative kinase, PCRK1, in immune signaling. We showed that pcrk1 mutants are more susceptible to Pseudomonas syringae than wild type plants suggesting that PCRK1 has a positive role in immune responses. We also showed that PCRK1 is important for immunity triggered by some of the conserved Microbe Associated Molecular Patterns (MAMP) as well endogenous signals generated as a result of pathogen activity called Damage Associated Molecular Patterns (DAMP).