Dehydroascorbate induces plant resistance in rice against root-knot nematode Meloidogyne graminicola.

Abstract

Ascorbic acid (AsA) is an important antioxidant in plants and regulates various physiological processes. In this study, we show that exogenous treatments with the oxidized form of AsA, i.e., dehydroascorbate (DHA) activates induced systemic resistance in rice against the root-knot nematode Meloidogyne graminicola and investigate the molecular and biochemical mechanisms underlying this phenotype. Detailed transcriptome analysis on roots of rice plants showed an early and robust transcriptional response upon foliar DHA-treatment, with induction of several genes related to plant stress responses, immunity, antioxidant activity, and secondary metabolism already at 1 day post-treatment. Quantitative and qualitative evaluation of H2O2 levels confirmed the appearance of a reactive oxygen species (ROS) burst upon DHA-treatment, both at the site of treatment and systemically. Experiments using chemical ROS inhibitors or scavengers confirmed that H2O2 accumulation contributes to DHA-based induced resistance. Furthermore, hormone measurements in DHA-treated plants showed a significant systemic accumulation of the defense hormone salicylic acid (SA). The role of the SA pathway in DHA-based IR was confirmed by nematode infection experiments using an SA-signaling deficient WRKY45-RNAi line and qRT-PCR on SA marker genes. Our results collectively reveal that DHA activates induced systemic resistance in rice against the root-knot nematode M. graminicola, mediated through the production of reactive oxygen species and activation of the salicylic acid pathway.