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

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 Ca2+ 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 Ca2+ 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 Ca2+. This study uncovers a novel mode of action by which CSL-gels trigger NbCML3 expression through the stable and sustained release of Ca2+.

Automated summary

Control of plant virus diseases often relies on synthetic chemical inducers, but the underlying molecular mechanisms are not well understood. In this study, a chitosan-coated lentinan-loaded hydrogel (CSL-gel) was developed and shown to protect plants from various virus infections. The CSL-gel exhibited the ability to sustain release lentinan and promote Ca2+ release. Application of CSL-gels on plant roots induced broad-spectrum resistance against plant viruses. Further analysis revealed that sustained release of Ca2+ from CSL-gel upregulated Nicotiana benthamiana calmodulin-like protein gene 3 (NbCML3), and modulating NbCML3 expression altered tobacco's susceptibility and resistance to TMV.