The rice GRH2 and GRH4 activate various defense responses to the green rice leafhopper and confer strong insect resistance

Rice GRH2 confers enhanced resistance to green rice leafhoppers (GRH), Nephotettix cincticeps Uhler. A pyramided line carrying GRH2 and GRH4 (TGRH29) showed strong resistance to GRH insects compared with a GRH2 near-isogenic line (TGRH11), although GRH4 alone did not confer any resistance to GRH. To explore the effects of GRH2 and GRH4 on GRH resistance, we investigated the transcriptional response of rice plants to GRH infestation using DNA microarray analysis. The expression of a large number of genes encoding pathogenesis-related proteins, lipoxygenases, terpene synthase (TPS) and WRKY transcription factor, was upregulated in response to GRH infestation in TGRH11 and TGRH29 compared with control plants. Quantitative RT-PCR revealed that expression of JAmyb and TPS was more strongly and more rapidly upregulated in TGRH29 compared with TGRH11 after GRH infestation. These results suggest that TGRH29 plants can more rapidly and strongly activate the defense response compared with plants carrying GRH2 alone. Furthermore, sesquiterpenes were emitted from TGRH29 plants in response to attack by GRH. The strong induction of sesquiterpene production in the TGRH29 line was correlated with the transcript levels of TPS genes. Our results suggest that GRH2 and GRH4 activate various defense responses and confer strong GRH insect resistance.