ABSTRACT Calmodulin‐like (CML) proteins are key regulators of calcium‐mediated signalling in plant immunity. In this study, we characterised SlCML51 in Solanum lycopersicum and investigated its role in resistance to tobacco mosaic virus (TMV). Phylogenetic analysis revealed that SlCML51 and SlCML43 belong to the same subfamily outside of the other CMLs. TMV infection significantly induced SlCML51 expression, particularly in leaves, suggesting its involvement in antiviral defence. Subcellular localisation analysis showed that SlCML51 is present in both the endoplasmic reticulum and nucleus, mirroring the localisation of most of the other CMLs. Functional characterisation via virus‐induced gene silencing demonstrated that SlCML51 positively regulates TMV resistance, as silenced plants exhibited increased TMV accumulation. Conversely, transient overexpression of SlCML51 in Nicotiana benthamiana suppressed viral replication. Mechanistic studies revealed that SlCML51 does not directly interact with TMV proteins but enhances resistance by activating the jasmonic acid (JA) pathway. Notably, SlCML51‐mediated defence was associated with reactive oxygen species (ROS) accumulation, and mutation of its Ca 2+ ‐binding domain attenuated its antiviral function. Furthermore, SlCML51 conferred resistance against Phytophthora capsici but enhanced infection by Pseudomonas syringae pv. tomato , reinforcing its role in basal immunity. Our findings highlight SlCML51 acting as a regulator of plant immunity. This study provides new insights into CML‐mediated immune responses and the interplay between JA and salicylic acid signalling in viral defence.
Luo et al. (Sun,) studied this question.