Uncovering the virulence function of the Ralstonia solanacearum TAL effector Brg11

Bacterial plant pathogens multiply in the intercellular space (apoplast) and never enter into host cells. Yet, using a syringe –like multiprotein complex they inject a cocktail of up to 100 distinct effector proteins into plant host cells that interfere in various ways with the host to collectively promote disease. Transcription Activator-Like Effector proteins (TALEs) are one class of effectors that function as transcription factors within the plant cell and that are found in several members of the bacterial genus Xanthomonas (Boch et al; New Phytologist 2014, 204:823). Upon injection, TALEs translocate to nucleus, bind to effector binding elements (EBEs) of plant target promoters, and activate the downstream host susceptibility (S) genes to promote disease. TALE-like proteins have been identified in the broad-host root pathogen Ralstonia solanacearum and have been designated as RipTALs. It has been demonstrated that RipTALs are capable to activate plant genes if these have a compatible EBE in their promoter. Yet, thus far no host S gene has been identified that would be transcriptionally activated by a RipTAL.
In the given PhD project we aim to characterize host target genes of the RipTAL Brg11. Previously, we determined the preferred EBE for Brg11 (de Lange et al; New Phytologist 2013, 199:773; Schandry et al; Frontiers in Plant Science 2016, 7). Using a bioinformatics approach we scanned multiple genomes of R. solanacearum host plants for the presence of the predicted EBE. This screen resulted in identification of one gene that contains an EBE which is highly conserved across all host species. Transcriptome profiling in tomato by RNA-Seq confirmed that identified target gene is transcriptionally activated in a Brg11-dependent fashion. The aim of the PhD project is to clarify how the identified Brg11 target gene promotes R. solanacearum.