Do fungi sleep?
Not quite the way humans or animals do. But across the living world, many organisms without brains or nervous systems follow cycles of activity and rest. Fungi are no exception.
Fungi operate on an internal schedule known as a circadian rhythm: a roughly 24-hour biological cycle that helps organisms anticipate and prepare for regular changes in their environment, such as day and night or warm and cold. For fungi, these rhythms are not about sleep in the way we understand it: there’s no dreaming or REM cycles. But fungi do seem to have periods of increased and decreased activity, coordinated by these internal biological clocks.
One of the first discoveries of circadian rhythm in fungi came from a species called Neurospora crassa, a type of orange mold often found on bread. In laboratory settings, researchers noticed that this fungus produces bands of spores in regular intervals, one band approximately every 24 hours, even when grown in complete darkness. That meant it was running on an internal timer.
Scientists eventually identified specific genes involved in maintaining this timer. One of the most important is frq (short for frequency), which behaves similarly to the per (short for period) gene found in animals. The frq gene plays a central role in what’s known as a negative feedback loop, a core mechanism in circadian biology across many species.
How the fungal clock ticks…
Here is a simplified version of how the core mechanisms work.
Every day, a pair of proteins known as the White Collar Complex (WCC) turns on the frq gene. The frq gene produces the FRQ protein, which gradually builds up in the cell. Once enough FRQ accumulates, it binds to another protein (an RNA helicase), and together they shut down the WCC, which inhibits further production of FRQ. Over time, FRQ is broken down by the cell. As its levels fall, the WCC becomes active again, and the cycle starts again. (more information can be found here)
Even though the clock can run on its own, it doesn’t stay perfectly aligned with the 24-hour day over time. The natural period of the rhythm might be, say, 22 to 25 hours, not exactly 24. That small mismatch means the clock would slowly drift out of sync with the real day-night cycle if left to run in total darkness. That’s when the blue light comes in. It acts as a signal that resets the internal clock every day, keeping it aligned with the Earth’s day-night schedule.
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As revealed in this article, while the frq gene is central to the circadian clock in Neurospora crassa, researchers have discovered that even when this gene is knocked out, the fungus can still show rhythmic behavior under certain conditions. This means that there is a secondary clock, known as the frq-less oscillator (FLO). Although this one is not as well-understood, it shows that fungi have multiple ways to keep time, depending on what is happening in their cells.
Even more fascinating is how this secondary clock can be activated. In experiments with mutant fungi lacking frq, researchers added a compound called menadione, which triggers internal chemical signals known as reactive oxygen species (ROS). Surprisingly, the fungi began to show rhythmic activity again.
Interested in exploring even more? Check these out:
https://pubmed.ncbi.nlm.nih.gov/39102446/
fungitopia.org 