Low-dose of oligosaccharins boosts antiviral immunity through induction of multiple defense pathways in rice

Abstract Oligosaccharins, widely recognized as plant immunity inducers, have been applied and studied for enhancing antiviral defenses in rice over the years. However, due to the complex induction mechanism in rice, further studies are needed. In this study, we demonstrated that oligosaccharins enhanced rice resistance to southern rice black-streaked dwarf virus (SRBSDV) at both the symptomatic and molecular levels. RNA-seq analysis revealed that oligosaccharins enhanced rice antiviral defense by activating multiple defense pathways. Among them, the jasmonic acid (JA) signaling pathway, a crucial antiviral pathway in rice, was investigated in detail. Interestingly, RNA-seq data showed that genes related to JA signaling pathway were significantly induced after 1 h but not after 24 h of oligosaccharins treatment, suggesting that JA induction by oligosaccharins was rapid and sensitive. Furthermore, JA levels and sensitivity analysis showed that oligosaccharins induced JA accumulation, making treated rice plants more sensitive to methyl jasmonate (MeJA). Additionally, oligosaccharins treatment also induced a burst of reactive oxygen species (ROS) in rice. Notably, oligosaccharins demonstrated a low-dose effect, within a certain dilution range from 6000-fold to 1000-fold diluted solution of 5% oligosaccharins, with the 4000-fold diluted solution exhibiting a stronger ability to induce elevated production of JA and ROS. Moreover, the application of low-dose oligosaccharins also enhanced rice resistance to SRBSDV. These data suggest that low-dose of oligosaccharins can enhance rice antiviral defense by inducing multiple defense pathways, including the JA signaling pathway and ROS production.