TAL effectors from Xanthomonas: design of a programmable DNA-binding specificity

Xanthomonas spp. are Gram-negative bacteria with powerful molecular weapons to attack their plant hosts. Key for pathogenicity of Xanthomonas is a type III secretion system that injects a cocktail of effector proteins into plant cells to function as potent virulence factors. TAL (transcription activator-like) effectors from Xanthomonas function as transcriptional activators of plant genes in the plant nucleus. They contain a central domain of tandem, near-identical 34 amino-acid repeats. Each repeat recognizes a single base pair in a contiguous DNA sequence and two adjacent hypervariable amino acids per repeat specify the base that is bound. This modular DNA-binding code allows a simple reprogramming of DNA-binding specificity, a feature with high potential for biotechnology. We developed a method called "Golden TAL Technology" that allows a flexible assembly of TAL proteins with a designed order of repeats.