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

Abstract

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.

Plastic Transcriptomes Stabilize Immunity to Pathogen Diversity: The Jasmonic Acid and Salicylic Acid Networks within the Arabidopsis/Botrytis Pathosystem

“…This suggests that this collection of B. cinerea genotypes does not contain large-effect qualitative virulence loci; instead, this generalist uses a highly polygenic virulence architecture (Denby et al, 2004;Finkers et al, 2007b;Rowe and Kliebenstein, 2008;Corwin et al, 2016b;Zhang et al, 2016). This agrees with previous B. cinerea mechanistic studies that identify a large collection of standing genetic variation that controls a wide range of specific virulence mechanisms (Choquer et al, 2007;Rowe and Kliebenstein, 2007;Noda et al, 2010;Rowe et al, 2010;Dalmais et al, 2011;Michielse et al, 2011;Shlezinger et al, 2011;Windram et al, 2012;Pearson and Bailey, 2013;Kumari et al, 2014;An et al, 2015;Atwell et al, 2015;Hevia et al, 2015;Plaza et al, 2015;Schumacher et al, 2015;Zhang et al, 2015a;Corwin et al, 2016aCorwin et al, , 2016bLopezCruz et al, 2017;Zhang et al, 2016). Taken together, this supports the perspective that the Arabidopsis-B.…”

Redox and the circadian clock in plant immunity: A balancing act

“…Altogether, the strongest accumulation of MYC2 happens during the daytime [38], which might help combat the higher herbivore activity during the day [35]. The day time JA peak does not seem to coincide with resistance against the necrotrophic fungus Botrytis cinerea , which is the strongest when the pathogen is inoculated at dawn [39,40]. This discrepancy was explained by the approximate 12-h delay required for the germination of B. cinerea conidiospores and the formation of infectious hyphae [40].…”

Natural Variation of the Circadian Clock in Neurospora

“…However, as we study the ecotypes (or accessions) of the model organisms that are adapted to a diverse habitat, we find significant deviations in these clocks from that of the reference strain. Circadian clocks have been observed in fungi other than N. crassa , however, these clocks are not satisfying the community-agreed criteria to be called an authentic circadian clock (Austin, 1968; Bluhm, Burnham, & Dunkle, 2010; Greene, Keller, Haas, & Bell-Pedersen, 2003; Hevia, Canessa, & Larrondo, 2016; Hevia, Canessa, Muller-Esparza, & Larrondo, 2015; Oliveira et al, 2015; Traeger & Nowrousian, 2015). We believe it is more interesting to find different kinds of clocks with different properties, which reflect the life history of the organism (or species) and speak volumes about the real biology of the clock in nature.…”