circadian oscillator in the fungus Botrytis cinerea regulates virulence when infecting Arabidopsis thaliana

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-07, Vol.112 (28), p.8744-8749
• Main Authors: Hevia, Montserrat A, Paulo Canessa, Hanna Müller-Esparza, Luis F. Larrondo
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - microbiology; Arabidopsis thaliana; Ascomycetes; Biological Sciences; Botrytis - pathogenicity; Botrytis - physiology; Botrytis cinerea; circadian clock; Circadian Rhythm; Culture Media; defense mechanisms; Flowers & plants; Fungi; Host-Pathogen Interactions; mutants; Mutation; Neurospora; Neurospora crassa; Pathogens; plant pathogenic fungi; plant–pathogen interaction; Virology; virulence; Virulence - genetics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1508432112

The circadian clock of the plant model Arabidopsis thaliana modulates defense mechanisms impacting plant–pathogen interactions. Nevertheless, the effect of clock regulation on pathogenic traits has not been explored in detail. Moreover, molecular description of clocks in pathogenic fungi—or fungi in general other than the model ascomycete Neurospora crassa —has been neglected, leaving this type of question largely unaddressed. We sought to characterize, therefore, the circadian system of the plant pathogen Botrytis cinerea to assess if such oscillatory machinery can modulate its virulence potential. Herein, we show the existence of a functional clock in B. cinerea , which shares similar components and circuitry with the Neurospora circadian system, although we found that its core negative clock element FREQUENCY (BcFRQ1) serves additional roles, suggesting extracircadian functions for this protein. We observe that the lesions produced by this necrotrophic fungus on Arabidopsis leaves are smaller when the interaction between these two organisms occurs at dawn. Remarkably, this effect does not depend solely on the plant clock, but instead largely relies on the pathogen circadian system. Genetic disruption of the B. cinerea oscillator by mutation, overexpression of BcFRQ1, or by suppression of its rhythmicity by constant light, abrogates circadian regulation of fungal virulence. By conducting experiments with out-of-phase light:dark cycles, we confirm that indeed, it is the fungal clock that plays the main role in defining the outcome of the Arabidopsis – Botrytis interaction, providing to our knowledge the first evidence of a microbial clock modulating pathogenic traits at specific times of the day. Circadian clocks are molecular machineries that allow organisms to anticipate daily cyclic challenges and to temporally modulate different processes. Thus, plant defense mechanisms against pathogens have been reported to vary daily in Arabidopsis thaliana . Although the plant–pathogen interaction is a two-sided story, nothing is known regarding circadian regulation of pathogenic traits. Herein we characterize a functional circadian clock in the necrotrophic fungal plant pathogen Botrytis cinerea , postulating additional roles for BcFRQ1, the Botrytis ortholog of the core clock component FREQUENCY of Neurospora crassa . By using different plant and Botrytis clock-null mutants, we demonstrate that the interaction between this pathogen and its host varies