Characterisation of TAL-efector-mediated resistance to citrus canker using a new variant of Xanthomonas citri

ROESCHLIN R.A.; MOLINA M.C.; UVIEDO F.; GARCIA L.; FAVARO M. A.; CHIESA M.A.; FORMENT J.; MARANO M. R.; GADEA J.

Halle (Saale)

Congreso; 6th Xanthomonas Genomics Conference & 2nd Annual EuroXanth Conference 2018; 2018

Martin Luther University Halle-Wittenberg

Xanthomonas citri subspecie citri (X. citri) is the causal agent of Asiatic citrus canker. We have identified a natural variant. X. citri AT, that triggers a host-specific defense response in Citrus limon and C. sinensis. X. citri AT triggers in resistant plants a hypersensitive response (HR-like) associated with the interference on biofilm development and arrest of bacterial growth, involving an extensive transcriptional re-programming. Furthermore, this defense response protects plants from disease upon subsequent challenges by pathogenic Xanthomonas.The X. citri AT bacterial gene causing the development of HR-like responses in the plant appears to be a short (7.5 repeats) variant of the pathogenic pthA4 TAL-effector. The mode of action of this short TAL is mediating transcriptional activation of plant genes, as mutated version of the TAL effector in nuclear localization hampers the triggering of the HR-like response and the SV40 nuclear localization signal restores the HR response. DNA-binding assays using double-stranded microarrays indicate that this short TAL-effector is able to bind DNA. Initial experiments in the identification of targets demonstrate that natural short TAL-effectors can bind DNA in a code-dependent manner and activate transcription. The identification of the gene responsible for the HR response is under way. This knowledge will help to rationally exploit the plant immune system as a biotechnological approach to manage citrus canker, and reveals biological functionality for short TAL-effectors.