From evasion to elicitation: A fungal effector turned into defense trigger

To succeed in parasitism, plant pathogens deploy an arsenal of secreted proteins known as effectors, which can reshape plant physiology to their advantage, modulating immune responses or even reprogramming plant cell fate (Hogenhout et al., 2009).They are often grouped by conserved motifs, such as the LysM domain, found in different fungi (Marshall et al., 2011; Kombrink et al. 2013).Plants also encode LysM-domain proteins like OsCEBip in rice, which perceives chitin fragments from fungal cell walls and triggers defense signaling through dimerization with its co-receptor OsCERK1 (Tanaka et al., 2013; Albert et al., 2020).To avoid this surveillance, fungi use LysM effectors to sequester these chitin fragments, hiding from the plant receptors (de Jonge et al. 2010).In this issue of Plant Physiology, Peng et al. ( 2025) uncover an example of molecular arms race involving Lasiodiplodia theobromae, a grapevine pathogen notorious for its wide host range and extensive secretome of over 900 proteins (Yan et al., 2018).Among these, the authors identified six LysM proteins, including LtLysM2, which contains a secretion signal and two LysM domains.Using yeast secretion trap and affinity precipitation assays, they confirmed LtLysM2's secretion and chitin-binding ability, suggesting that L. theobromae uses this effector to evade a yet undescribed grapevine chitin receptor (Figure 1).When grapevine (Vitis vinifera) shoots were inoculated with L. theobromae overexpressing LtLysM2, the resulting lesions were longer than with the control fungus, whereas silencing the gene reduced symptoms, establishing its role in virulence.A yeast two hybrid (Y2H) screen revealed that LtLysM2 interacts with VvSrc2, a grapevine protein with a C2 domain, transmembrane (TM) domain and nuclear localization signal (NLS).C2 domains, which often bind Ca 2+ , are known players in plant defense signaling, and have been shown to be involved in different processes, including regulation of programmed cell death (Yang et al., 2007) and response to abiotic stresses (de Silva et al. 2011).The interaction between LtLysM2 and VvSrc2 was confirmed by Y2H, pull down assay and bimolecular fluorescence complementation (BiFC) assay.Transient expression of VvSrc2 in N. benthamiana confirmed its accumulation in the cell membrane and nucleus.Investigation of truncated fragments using transient expression showed that the C2 domain and the NLS motif were associated with membrane and nuclear localizations, respectively.Co-infiltration of N. benthamiana with LtLysM2 and VvSrc2