A lentinan-loaded calcium alginate hydrogel with a core-shell structure induces broad-spectrum resistance to plant viruses by activating CML19

Control of plant virus diseases largely depends on the induced plant defense achieved by the external application of synthetic chemical inducers with the ability to modify defense-signaling pathways. However, most of the molecular mechanisms underlying these chemical inducers remain unknown. Here, we developed a lentinan-loaded hydrogel with a core-shell structure and discovered how it protects plants from different virus infections. The hydrogel was synthesized by adding a chitosan shell on the surface of the polyanion sodium alginate-Ca2+-lentinan (LNT) hydrogel (SL-gel) to form a CSL-gel. CSL-gels exhibit the capacity to prolong the stable release of lentinan and promote Ca2+ release. Application of CSL-gels on the root of plants induces broad-spectrum resistance against TMV, TRV, PVX and TuMV). RNA-seq analysis identified that the calmodulin-like protein 19 gene (CML19) is upregulated by the sustained release of Ca2+ from the CSL-gel, and silencing and overexpression of CML19 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 Ca2+. This study uncovers a novel mode of action by which CSL-gels trigger CML19 expression through the stable and sustained release of Ca2+.