Researchers uncover role of fungal circadian clock in pathogenicity

Fusarium oxysporum is a soil-borne fungal pathogen that causes a group of serious plant diseases known as Fusarium wilts. As one of most economically important plant pathogens worldwide, it can infect hundreds of species—including major crops like tomatoes, bananas, cotton, and melons—causing wilting, stunting, and plant death. Understanding how F. oxysporum overcomes host defenses to increase pathogenicity is critical to mitigating its agricultural impact.

Now a team of scientists led by Prof. LIU Xiao from the Institute of Microbiology of the Chinese Academy of Sciences (CAS) has uncovered a crucial link between the fungus' circadian clock and its pathogenicity, offering new insight into how F. oxysporum adapts to its host environment. The study reveals that the circadian clock plays a pivotal role in regulating the fungus' response to zinc starvation—a core plant defense strategy—as well as in controlling secondary metabolism, thereby enhancing its virulence.

The findings, which provide a fresh perspective on host-pathogen interactions, were published on March 28 in Science Advances.

Circadian clocks are biological timekeeping systems that allow organisms to synchronize physiological processes with daily environmental cycles. While these clocks are known to affect immune responses in host organisms, their role in modulating pathogen virulence has remained largely unexplored—until now.

This study confirms the presence of a functional circadian clock in F. oxysporum, characterized by a negative feedback loop involving the transcription factors FoWC1, FoWC2, and the core clock protein FoFRQ. Among multiple Fofrq genes contributing to the circadian oscillator, Fofrq1 was identified as the primary regulator.

Using clock-deficient fungal mutants, the researchers demonstrated that circadian clock genes are essential for the pathogen's virulence. Additional experiments showed that fungal virulence varies diurnally under clock control—meaning the fungus's ability to infect plants fluctuates depending on the time of day.

A time-series transcriptome analysis further revealed rhythmic expression patterns in numerous genes, especially transcription factors and metabolic genes—some of which overlap with known pathogenic factors. These clock-regulated pathways help F. oxysporum mitigate zinc starvation stress and boost the production of fusaric acid, a key phytotoxin that enhances its infectivity.

This study underscores the significant role of the fungal circadian clock in orchestrating pathogenesis and host invasion, paving the way for innovative approaches to crop protection.

The research was conducted in collaboration with researchers from Yunnan University, Henan University, China Agricultural University, and the University of Texas Southwestern Medical Center. It was supported by the Beijing Natural Science Foundation, the Strategic Priority Research Program of CAS, and the National Natural Science Foundation of China.