A TAL effector repeat architecture for frameshift binding

Abstract

Transcription activator-like effectors (TALEs) are important Xanthomonas virulence factors that bind DNA via a unique tandem 34-amino-acid repeat domain to induce expression of plant genes. So far, TALE repeats are described to bind as a consecutive array to a consecutive DNA sequence, in which each repeat independently recognizes a single DNA base. This modular protein architecture enables the design of any desired DNA-binding specificity for biotechnology applications. Here we report that natural TALE repeats of unusual aminoacid sequence length break the strict one repeat-to-one base pair binding mode and introduce a local flexibility to TALE-DNA binding. This flexibility allows TALEs and TALE nucleases to recognize target sequence variants with single nucleotide deletions. The flexibility also allows TALEs to activate transcription at allelic promoters that otherwise confer resistance to the host plant.

XA23 Is an Executor R Protein and Confers Broad-Spectrum Disease Resistance in Rice

“…The weak binding of AvrXa23-EBE AvrXa23 might also reflect a strategy of Xoo to avoid too easy activation of those genes (e.g., Xa23), whose expression cause very strong HR in host cell. In other words, the non-prevalent RVDs, together with the 18th aberrant repeat, confer TALE-binding flexibility on AvrXa23 to avoid a strong penalty on its overall activity; similar phenomena have been observed in research on the AvrXa7 and PthXo2 (Richter et al, 2013). Because avrXa23 is widespread in Xoo strains (Wang et al, 2014a), we think that AvrXa23 would contribute to the virulence of Xoo for infection or growth in host plants.…”

“…Four transmembrane helices (M1-M4) of XA10 are underlined in green. Asterisks indicate the amino acid positions 10, 30, 50, 70, 90, 110 and 130. to loop out (Richter et al, 2013). Accordingly, the 18th repeat of AvrXa23, containing 42 aa (Wang et al, 2014a), might also affect the protein-DNA interaction and weaken the binding to EBE AvrXa23 .…”

Behind the lines–actions of bacterial type III effector proteins in plant cells

“…Experimental evidence suggests that shorter or longer repeats bind to matching nucleotides of the EBE or are excluded from binding (Richter et al. 2014). The looping-out of repeats allows a shift of the following repeats by one nucleotide position in the EBE.…”

Means to optimize protein expression in transgenic plants

“…One way to achieve a time-specific and tissue-specific control is targeted transcription activation of proteins influencing important OF factors. Here, research on plant virus mediated gene expression becomes more and more attractive to the field of biotechnology, and transcription activator-like effectors are used to selectively activate gene expression in transgenic plants [35], accompanied by bioinformatics tools to predict the DNA binding target sites of interest [36,37]. However, the targeted gene regulation is not new in the field and DNA-binding proteins like zinc finger proteins have been well studied, enabling an engineered binding to virtually any locus in vitro [38].…”