A chitosan‐coated lentinan‐loaded calcium alginate hydrogel induces broad‐spectrum resistance to plant viruses by activating Nicotiana benthamiana calmodulin‐like (CML) protein 3

Abstract Control of plant virus diseases largely depends on the induced plant defence achieved by the external application of synthetic chemical inducers with the ability to modify defence‐signalling pathways. However, most of the molecular mechanisms underlying these chemical inducers remain unknown. Here, we developed a chitosan‐coated lentinan‐loaded hydrogel and discovered how it protects plants from different virus infections. The hydrogel was synthesized by coating chitosan on the surface of the calcium alginate‐lentinan (LNT) hydrogel (SL‐gel) to form a CSL‐gel. CSL‐gels exhibit the capacity to prolong the stable release of lentinan and promote Ca 2+ release. Application of CSL‐gels on the root of plants induces broad‐spectrum resistance against plant viruses (TMV, TRV, PVX and TuMV). RNA‐seq analysis identified that Nicotiana benthamiana calmodulin‐like protein gene 3 ( NbCML3 ) is upregulated by the sustained release of Ca 2+ from the CSL‐gel, and silencing and overexpression of NbCML alter the susceptibility and resistance of tobacco to TMV. Our findings provide evidence that this novel and synthetic CSL‐gel strongly inhibits the infection of plant viruses by the sustainable release of LNT and Ca 2+ . This study uncovers a novel mode of action by which CSL‐gels trigger NbCML3 expression through the stable and sustained release of Ca 2+ .