Evaluating the role of light and of a circadian clock in the virulence of the necrotrophic fungus Botrytis cinerea
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Date
2015
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Abstract
Disease establishment and progression depends on many variable factors, being environmental signals key elements that regulate development and behavior. Recently, it has been suggested that the susceptibility of the host and the virulent potential of the hostile organism seem to differ with light-dark cycles occurring within a 24-hour day, which suggests that the outcome of the plant-pathogen interaction might be controlled by light and by an endogenous timekeeping mechanism. Circadian clocks allow organisms to anticipate predictable daily changes and a few reports in plants exemplify anticipatory mechanisms, as for example defense responses by the time when the pathogen attack is most likely to happen. Nevertheless, this concept has never been evaluated in pathogens, like fungi.Surprisingly, the only fungus in which a circadian clock has been molecularly characterized is the non-pathogenic ascomycete Neurospora crassa, while on the other hand, molecular mechanisms linking light sensing and virulence have never been evaluated in necrotrophic fungi. Therefore, we have studied the role of light and circadian regulation in the necrotrophic fungus Botrytis cinerea, which ranks as the second most important phytopathogen according to its economic and scientific importance. In this thesis, I report how light modulates phenotypical responses and how activates changes in gene expression in B. cinerea. By generating a knockout strain for the putative blue light photoreceptor and transcription factor BcWCL1 we have shown that it mediates some, but not all light responses. Also, this mutant is more sensitive to oxidative stress in a light dosis-dependent manner. Using Arabidopsis thaliana as a host plant, we show an altered infection process for the Δbcwcl1 strain when light is present.In addition, we have characterized a functional circadian clock in B. cinerea, demonstrating that the BcFRQ1 protein and a transcriptional complex formed by BcWCL1 and BcWCL2 are part of the circuitry of an oscillator. By generating a Δfrq1 strain, we unveiled that this protein not only serves an important circadian role, but that it also has additional functions, impacting sexual/asexual developmental decisions. Taking advantage of the clock mutants that we generated and of available plant arrhythmic ecotypes, we provide compelling evidence that the outcome of the plant- fungal pathogen interaction varies with the time of day, in a manner that is largely dependent on the fungal clock. To our knowledge, these results provide the first evidence of a functional light and circadian machinery in a pathogenic fungus, confirming that components of the circadian clock (including the putative photoreceptor BcWCL1) modulate the plant-pathogen interaction from a fungal perspective. Finally, this work open up the basis for environmental and natural ways to control this major and worldwide necrotrophic fungal plant pathogen.
Description
Tesis (Doctor en Ciencias Biológicas, mención Genética Molecular y Microbiología)--Pontificia Universidad Católica de Chile, 2015