The OsWRKY6 transcriptional cascade functions in basal defense and Xa1-mediated defense of rice against Xanthomonas oryzae pv. oryzae.

ABSTRACT

MAIN CONCLUSION: The rice protein OsWRKY6 directly activates OsWRKY45 and OsWRKY47 expression, and also activates OsPR1a and OsPR1b through the two OsWRKYs, and this transcriptional module participates in Xa1-mediated defense against the pathogen Xanthomonas oryzae pv. oryzae. Biotic stress, the pathogen Xanthomonas oryzae pv. oryzae (Xoo) in particular, negatively impacts worldwide productivity and yield in the staple crop rice (Oryza sativa). OsWRKY transcription factors are involved in various biotic stress responses in rice, and OsWRKY6 specifically acts as an important defense regulator against Xoo. However, the relationship between OsWRKY6 and other OsWRKYs, as well as its role in resistance (R) gene-mediated defense, have yet to be studied in depth. Here, we characterized a transcriptional cascade triggered by OsWRKY6 that regulated defense against Xoo infection mediated by the NBS-LRR protein Xa1. OsWRKY45 and OsWRKY47 were identified as direct transcriptional targets of OsWRKY6, and their two gene products reciprocally activated their two genes. Furthermore, OsWRKY6 activated OsPR1a and OsPR1b via the OsWRKY45 and OsWRKY47. Two OsWRKY6 RNAi knockdown lines showed significantly reduced defense even against an incompatible Xoo infection, and the expression of OsWRKY6 was not regulated by OsWRKY51 and OsWRKY88. This study reveals that a novel downstream transcriptional pathway activated by OsWRKY6 is involved in Xa1-mediated defense against Xoo.