Thigmo Responses: The Fungal Sense of Touch

Abstract

The growth and development of most fungi take place on a two-dimensional surface or within a three-dimensional matrix. The fungal sense of touch is therefore critical for fungi in the interpretation of their environment and often signals the switch to a new developmental state. Contact sensing, or thigmo-based responses, include thigmo differentiation, such as the induction of invasion structures by plant pathogens in response to topography; thigmonasty, where contact with a motile prey rapidly triggers its capture; and thigmotropism, where the direction of hyphal growth is guided by physical features in the environment. Like plants and some bacteria, fungi grow as walled cells. Despite the well-demonstrated importance of thigmo responses in numerous stages of fungal growth and development, it is not known how fungal cells sense contact through the relatively rigid structure of the cell wall. However, while sensing mechanisms at the molecular level are not entirely understood, the downstream signaling pathways that are activated by contact sensing are being elucidated. In the majority of cases, the response to contact is complemented by chemical cues and both are required, either sequentially or simultaneously, to elicit normal developmental responses. The importance of a sense of touch in the lifestyles and development of diverse fungi is highlighted in this review, and the candidate molecular mechanisms that may be involved in fungal contact sensing are discussed.

Experimental Models of Dermatophytosis

“…These results suggest that dermatophytes are able to degrade intercellular junctions (e.g., corneodesmosomes or tight junctions) and/or the extracellular lipid matrix. In addition, these observations also suggest that hyphal elongation is orientated according to the physical and topographical features of the substrate in order to facilitate its invasion, a phenomenon known as "thigmotropism" [76]. This ability of dermatophytes to orientate their growth was also described by Perera et al [77] who observed the growth of Epidermophyton floccosum, M. canis, and T. mentagrophytes on artificial membranes.…”

Analysis of the competitiveness between a non-aflatoxigenic and an aflatoxigenic Aspergillus flavus strain on maize kernels by droplet digital PCR

“…This suggests that the inhibition of the AF biosynthesis does not depend directly on the actual inoculated ratio of the two strains. It still has to be clarified in further experiments whether this inhibition acts on levels beyond the thigmotropic or competitive exclusion principles (Cotty and Bayman 1993 ; Almeida and Brand 2017 ).…”

“…Possible mechanisms are competition for nutrients and competitive exclusion, which is a thigmo-based response (Cotty and Bayman 1993 ; Huang et al 2011 ). Thigmo-based responses are mediated by direct contact between the fungal cells and the environment (Almeida and Brand 2017 ).…”

Biomechanics of Hyphal Growth

“…Adapting growth to penetrate substrates is related to two sensorresponse systems: chemotropism (Turrà et al, 2016) and thigmotropism (Almeida and Brand, 2017). The biochemical mechanisms underlying chemo-and mechano-sensing are very diverse, and generally result in activation of MAP kinase and cAMP signaling cascades (Turrà et al, 2016;Braunsdorf et al, 2016).…”