Breaking the Code of DNA Binding Specificity of TAL-Type III Effectors

TLDR

Many bacteria rely on type III secretion to inject effector proteins that manipulate host cells, and TAL effectors from Xanthomonas are key virulence factors that bind DNA in the plant nucleus via tandem repeat domains. The study aims to elucidate how TAL effectors encode target DNA specificity. Each repeat contains two hypervariable residues that recognize a single base pair of the target DNA. We predicted and experimentally confirmed TAL effector recognition sequences, demonstrated that their modular architecture permits construction of artificial effectors with novel specificities, and showed that this distinct DNA‑binding domain can be harnessed for biotechnological applications.

Abstract

The pathogenicity of many bacteria depends on the injection of effector proteins via type III secretion into eukaryotic cells in order to manipulate cellular processes. TAL (transcription activator-like) effectors from plant pathogenic Xanthomonas are important virulence factors that act as transcriptional activators in the plant cell nucleus, where they directly bind to DNA via a central domain of tandem repeats. Here, we show how target DNA specificity of TAL effectors is encoded. Two hypervariable amino acid residues in each repeat recognize one base pair in the target DNA. Recognition sequences of TAL effectors were predicted and experimentally confirmed. The modular protein architecture enabled the construction of artificial effectors with new specificities. Our study describes the functionality of a distinct type of DNA binding domain and allows the design of DNA binding domains for biotechnology.