Breaking the DNA binding code of Ralstonia solanacearum TAL effectors provides new possibilities to generate plant resistance genes against bacterial wilt disease
De Lange O, Schreiber T, Schandry N, Radeck J, Braun K-H, Koszinowski J, Heuer H, Strauß A, Lahaye T
- Ralstonia solanacearum is a devastating bacterial phytopathogen with a broad host range. R. solanacearum injected effector proteins (Rips) are key to the successful invasion of host plants. We have characterised Brg11, the first identified member of a class of Rips with high sequence similarity to the transcription activator-like (TAL) effectors of Xanthomonas spp, collectively termed RipTALs.
- Fluorescence microscopy of in planta expressed RipTALs showed nuclear localisation. Domain swaps between Brg11 and Xanthomonas TAL effector (TALE) AvrBs3 showed the functional interchangeability of DNA binding and transcriptional activation domains. PCR was used to determine the sequence of brg11 homologs from strains infecting phylogenetically diverse host plants.
- Brg11 localises to the nucleus and activates promoters containing a matching effector binding element (EBE). Brg11 and homologs preferentially activated promoters containing EBEs with a 5’ terminal guanine contrasting with the TALE preference for a 5’ thymine.
- Brg11 and other RipTALs likely promote disease through the transcriptional activation of host genes. Brg11 and the majority of homologs identified in this study were shown to activate similar or identical target sequences, in contrast to TALEs, which generally show highly diverse target preferences. This information provides new options to engineer plants resistant to R. solanacearum.