Cheng H¹, Li H¹, Deng Y¹, Xiao J¹, Li X¹, Wang S².

Plant Physiol. 2015 Jan 26. pii: pp.114.256016. [Epub ahead of print]

Abstract

Blast caused by fungal Magnaporthe oryzae is a devastating disease of rice worldwide, and this fungus also infects barley. At least 11 rice WRKY transcription factors have been reported to regulate rice response to M. oryzae either positively or negatively. However, the relationships of these WRKYs in the rice defense signaling pathway against M. oryzae are unknown. Previous studies have revealed that rice WRKY13 (as a transcriptional repressor) and WRKY45-2 enhance resistance to M. oryzae. Here we show that rice WRKY42, functioning as a transcriptional repressor, suppresses resistance to M. oryzae. WRKY42-RNA interference (RNAi) and WRKY42-overexpressing (oe) plants showed increased resistance and susceptibility to M. oryzae, accompanied by increased or reduced jasmonate acid (JA) content, respectively, compared with wild-type plants. JA pretreatment enhanced the resistance of WRKY42-oe plants to M. 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 M. 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 M. 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 M. oryzae.

See http://www.ncbi.nlm.nih.gov/pubmed/25624395

Figure 7. Rice double gene mutants showed different responses to M. oryzae compared with their parent plants (single gene mutants). Rice plants were inoculated with M. oryzae isolate N2-2 at the four-leaf stage. Bars represent mean (three replicates for gene expression and 21 to 27 plants for disease index) ± standard deviation. The "a" and "b" indicate that a significant difference between transgenic and wild-type (WT; Mudanjiang 8) plants was detected at P < 0.05 and P < 0.01, respectively. A, WRKY13- overexpressing (oe) WRKY42-oe double mutant showed increased susceptibility compared with WRKY13-oe plants. B, WRKY13-RNAi WRKY45-2-oe double mutant showed increased susceptibility to M. oryzae compared with WRKY45-2-oe plants and reduced susceptibility compared with WRKY13-RNAi plants.