Local calcium signal transmission in mycelial network exhibits decentralized stress responses

Abstract

Many fungi live as mycelia, which are networks of hyphae. Mycelial networks are suited for the widespread distribution of nutrients and water. The logistical capabilities are critical for the extension of fungal survival areas, nutrient cycling in ecosystems, mycorrhizal symbioses, and virulence. In addition, signal transduction in mycelial networks is predicted to be vital for mycelial function and robustness. A lot of cell biological studies have elucidated protein and membrane trafficking and signal transduction in fungal hyphae; however, there are no reports visualizing signal transduction in mycelia. This paper, by using the fluorescent Ca2+ biosensor, visualized for the first time how calcium signaling is conducted inside the mycelial network in response to localized stimuli in the model fungus Aspergillus nidulans. The wavy propagation of the calcium signal inside the mycelium or the signal blinking in the hyphae varies depending on the type of stress and proximity to the stress. The signals, however, only extended around 1,500 μm, suggesting that the mycelium has a localized response. The mycelium showed growth delay only in the stressed areas. Local stress caused arrest and resumption of mycelial growth through reorganization of the actin cytoskeleton and membrane trafficking. To elucidate the downstream of calcium signaling, calmodulin, and calmodulin-dependent protein kinases, the principal intracellular Ca2+ receptors were immunoprecipitated and their downstream targets were identified by mass spectrometry analyses. Our data provide evidence that the mycelial network, which lacks a brain or nervous system, exhibits decentralized response through locally activated calcium signaling in response to local stress.

Foraging strategies of fungal mycelial networks: responses to quantity and distance of new resources

“…Furthermore, the migration decision of P. velutina mycelium was affected by the waiting time for the bait, i.e., the quality change of the original inoculum wood (Fukasawa and Kaga, 2021). If mycelium, as a modular organism, responds locally to these environmental stimuli (Itani et al, 2023), the NEAR experiment in the present study may have resulted in two separate parts of the mycelium responding to the bait, more or less, independently: the small part of the mycelium close to the original inoculum, and the larger spreading fans, including the growing front. Given that most of the nutrients are likely directed toward the growing front, the small part of the mycelium must respond to the new bait without a sufficient allocation of nutrients, which likely induces migration.…”

Harnessing Fungi Signaling in Living Composites

“…[85] R-GECO, based on a red fluorescent protein (RFP) characterized by a red-shifted emission, enables deep-tissue imaging and has been employed to investigate wavy propagation and blinking calcium signals in externally stimulated Aspergillus nidulans. [86] GCaMP probes, typically sourced from the fusion of calmodulin, M13 peptide, and green fluorescent protein (GFP), emit green fluorescence upon binding to calcium ions. [87] Live-cell imaging of fungal cells shows Ca 2+ -specific responses in Candida albicans exposed to membrane, osmotic, and oxidative stressors [88] and Saccharomyces cerevisiae in response to pheromones.…”

Electrical integrity and week-long oscillation in fungal mycelia

“…Similarly, Fukasawa et al 25 reported that the fruit bodies of an ectomycorrhizal fungus Laccaria bicolor exhibited electrical potential following a rainfall event, with causal relationships observed in their patterns across the neighboring fruit bodies. Nonetheless, this transfer of electrical signals across the entirety of the mycelia remains a subject of debate and ongoing research 26 .…”