Pyrroloquinoline Quinone Treatment Induces Rice Resistance to Sheath Blight through Jasmonic Acid Pathway

Using bioactive inducers to enhance rice resistance is an effective means of green prevention and control of diseases during rice production. In a previous study, we found that foliar sprays of pyrroloquinoline quinone (PQQ) as the bioactive inducer could remarkably reduce the occurrence index of rice sheath blight (ShB) Rhizoctonia solani and increase the grain yield of rice under field conditions. However, little information is available on the mechanism of PQQ-induced rice resistance to ShB. In this study, the phenotype and mechanism of foliar sprayed PQQ-induced rice resistance to ShB were investigated by artificial inoculation method, RNA-seq technology, and quantitative real-time PCR (qRT-PCR) assay in the laboratory. The results showed that at 144 h after inoculation (hai) with the ShB C30 strain, many disease spots occurred obviously in a susceptible variety, Lemont (L), treated by 1.0 μmol/L PQQ (P+) with the disease score (DS) of 4.36, and almost all plants were withered and died under the ddH2O (P−) treatment alone, with the DS of 8.39. By comparison, the DS of a resistant variety, Gaopin 6 (G), was only 0.88 in the P+ treatment and 3.82 in the P− treatment. The results of hormone determination showed that jasmonic acid (JA) contents in the G and L varieties treated by P+ were increased significantly, by 78% and 197% respectively, at 48 hai. There was no significant difference in salicylic acid (SA) contents in these varieties between P+ and ddH2O (P−) treatments during the period of 48 hai. These results suggest that JA may play a key role in PQQ-induced rice resistance to ShB. The transcriptome analysis of the leaf sheath of the G and L varieties indicated that 165 and 250 differentially expressed genes (DEGs) were found in the intersection of LP− vs. LP+ and GP− vs. GP+ at 24 and 48 hai, respectively. Kyoto encyclopedia of genes and genomes analysis showed that these DEGs were related to plant–pathogen interaction, ribosome, plant hormone signaling transduction, mitogen-activated protein kinas signaling pathway, and phenylpropanoid biosynthesis. For ten highly expressed genes related to disease resistance, the results of qRT-PCR assay showed that eight genes, especially OsAOS2 and OsOSM1, were regulated positively, and two genes, OsGF14e and OsWRKY72, were regulated negatively. Among these, four up-regulated genes, OsOSM1, OsAOS2, OsHI-LOX, and OsLOX1, and one down-regulated gene, OsWRKY72, belonging to the JA signaling pathway, may be involved in PQQ-induced rice resistance to ShB. These results provide valuable information for green prevention and control of ShB by PQQ foliar spraying in the field.