The WRKY45-2 WRKY13 WRKY42 Transcriptional Regulatory Cascade Is Required for Rice Resistance to Fungal Pathogen

Blast caused by fungal Magnaporthe oryzae is a devastating disease of rice (Oryza sativa) worldwide, and this fungus also infects barley (Hordeum vulgare). At least 11 rice WRKY transcription factors have been reported to regulate rice response to Magnaporthe oryzae either positively or negatively. However, the relationships of these WRKYs in the rice defense signaling pathway against Magnaporthe oryzae are unknown. Previous studies have revealed that rice WRKY13 (as a transcriptional repressor) and WRKY45-2 enhance resistance to Magnaporthe oryzae. Here, we show that rice WRKY42, functioning as a transcriptional repressor, suppresses resistance to Magnaporthe oryzae. WRKY42-RNA interference (RNAi) and WRKY42-overexpressing (oe) plants showed increased resistance and susceptibility to Magnaporthe oryzae, accompanied by increased or reduced jasmonic acid (JA) content, respectively, compared with wild-type plants. JA pretreatment enhanced the resistance of WRKY42-oe plants to Magnaporthe oryzae. WRKY13 directly suppressed WRKY42. WRKY45-2, functioning as a transcriptional activator, directly activated WRKY13. In addition, WRKY13 directly suppressed WRKY45-2 by feedback regulation. The WRKY13-RNAi WRKY45-2-oe and WRKY13-oe WRKY42-oe double transgenic lines showed increased susceptibility to Magnaporthe oryzae compared with WRKY45-2-oe and WRKY13-oe plants, respectively. These results suggest that the three WRKYs form a sequential transcriptional regulatory cascade. WRKY42 may negatively regulate rice response to Magnaporthe oryzae by suppressing JA signaling-related genes, and WRKY45-2 transcriptionally activates WRKY13, whose encoding protein in turn transcriptionally suppresses WRKY42 to regulate rice resistance to Magnaporthe oryzae.