Walking on a tightrope: cell wall‐associated kinases act as sensors and regulators of immunity and symbiosis

Abstract

Walking on a tightrope: cell wallassociated kinases act as sensors and regulators of immunity and symbiosisChoosing between symbiosis-and immunity-related responses is a decision that plants have to make continuously. As they grow in the soil and the atmosphere, their epidermal cells are probed by a multitude of microbes, attracted by the wealth of organic molecules that plants accumulate in their tissues through photosynthesis. Among this crowd of plant-interacting microorganisms, fungi are an important and particularly challenging group. While symbiotic fungi will gently enter the root tissues offering to trade organic molecules for mineral nutrients, several pathogens will attempt a destructive attack, digesting cell walls and heading straight towards the starchstuffed parenchymal tissues. The sooner a plant recognises who is who, the better its chances to survive. Indeed, the study of plant perception of fungal signals (Oldroyd, 2013) and downstream activation of signalling pathways (Giovannetti et al., 2024) and appropriate responses has driven several decades of investigation, depicting a complex scenario that has been more exhaustively clarified in the case of pathogenic interactions (Dodds et al., 2024). Our understanding of plant-fungus signalling in mycorrhizal symbioses is undoubtedly less complete (Genre et al., 2020). However, a number of studies have shed light on a few key elicitors, their receptors and the signal transduction pathways (Crosino & Genre, 2022) that mediate fungal accommodation in arbuscular mycorrhizas (AM) through the regulation of plant gene expression and cell reorganisation (MacLean et al., 2017).