Whispering Through the Leaves: Elucidating the Mechanical Perception and Downstream Defence Response Against Herbivory.

Insect herbivory generates not only tissue loss but also a suite of biophysical and chemical cues that plants must detect and interpret. To cope with these challenges, plants have evolved specialised structures and molecular mechanisms that perceive mechanical inputs and translate them into coordinated defence responses. This review summarises the concept of mechanostimulation during insect feeding, with a focus on how plants recognise mechanical cues and integrate them into broader defence signalling networks. We outline the types of stimuli generated during herbivory, the morphological and molecular sensors involved in mechanoperception, and the electrical signalling processes that mediate intra- and inter-cellular communication of long-distance signal transmission, for which the vascular system, particularly the phloem and xylem, emerges as a critical conduit. We further discuss how mechanostimulation interfaces with hormonal pathways and transcriptional regulation, ultimately activating defence genes. This framework is further extended to non-vascular plants such as bryophytes, where mechanosensing and defence occur in the absence of vascular tissues, shedding light on how these strategies originated and evolved in early land plants. Collectively, these insights provide a comprehensive framework for understanding how mechanostimulation shapes plant defence and offers avenues for future research in enhancing crop resilience.