TAL effectors: function, structure, engineering and applications
ABSTRACT TAL effectors are proteins secreted by bacterial pathogens into plant cells, where they enter the nucleus and activate expression of individual genes. TAL effectors display a modular architecture that includes a central DNA-binding region comprising a tandem array of nearly identical repeats that are almost all 34 residues long. Residue number 13 in each TAL repeat (one of two consecutive polymorphic amino acids that are termed 'repeat variable diresidues', or 'RVDs') specifies the identity of a single base; collectively the sequential repeats and their RVDs dictate the recognition of sequential bases along one of the two DNA strands. The modular architecture of TAL effectors has facilitated their extremely rapid development and application as artificial gene targeting reagents, particularly in the form of site-specific nucleases. Recent crystallographic and biochemical analyses of TAL effectors have established the structural basis of their DNA recognition properties and provide clear directions for future research.
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ABSTRACT: Xanthomonas phytopathogenic bacteria produce unique transcription activator-like effector (TALE) proteins that recognize and activate specific plant promoters through a set of tandem repeats. A unique TALE-DNA-binding code uses two polymorphic amino acids in each repeat to mediate recognition of specific nucleotides. The order of repeats determines effector's specificity toward the cognate nucleotide sequence of the sense DNA strand. Artificially designed TALE-DNA-binding domains fused to nuclease or activation and repressor domains provide an outstanding toolbox for targeted gene editing and gene regulation in research, biotechnology and gene therapy. Gene editing with custom-designed TALE nucleases (TALENs) extends the repertoire of targeted genome modifica-tions across a broad spectrum of organisms ranging from plants and insect to mammals.Briefings in functional genomics 06/2014; 13(5). DOI:10.1093/bfgp/elu013 · 3.43 Impact Factor
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ABSTRACT: CRISPR/Cas9 and TALEN are currently the two systems of choice for genome editing. We have studied the efficiency of the TALEN system in rice as well as the nature and inheritability of TALEN-induced mutations and found important features of this technology. The N287C230 TALEN backbone resulted in low mutation rates (0-6.6%), but truncations in its C-terminal domain dramatically increased efficiency to 25%. In most transgenic T0 plants, TALEN produced a single prevalent mutation accompanied by a variety of low-frequency mutations. For each independent T0 plant, the prevalent mutation was present in most tissues within a single tiller as well as in all tillers examined, suggesting that TALEN-induced mutations occurred very early in the development of the shoot apical meristem. Multigenerational analysis showed that TALEN-induced mutations were stably transmitted to the T1 and T2 populations in a normal Mendelian fashion. In our study, the vast majority of TALEN-induced mutations (~81%) affected multiple bases and ~70% of them were deletions. Our results contrast with published reports for the CRISPR/Cas9 system in rice, in which the predominant mutations affected single bases and deletions accounted for only 3.3% of the overall mutations. © 2015 Society for Experimental Biology, Association of Applied Biologists and John Wiley & Sons Ltd.Plant Biotechnology Journal 04/2015; DOI:10.1111/pbi.12372 · 5.68 Impact Factor
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ABSTRACT: Bacteria have many export and secretion systems that translocate cargo into and across biological membranes. Seven secretion systems contribute to pathogenicity by translocating proteinaceous cargos that can be released into the extracellular milieu or directly into recipient cells. In this review, we describe these secretion systems and how their complexities and functions reflect differences in the destinations, states, functions, and sizes of the translocated cargos as well as the architecture of the bacterial cell envelope. Weexamine the secretion systems from the perspective of pathogenic bacteria that proliferate within plant tissues and highlight examples of translocated proteins that contribute to the infection and disease of plant hosts. Expected final online publication date for the Annual Review of Phytopathology Volume 52 is August 04, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.Annual Review of Phytopathology 01/2014; DOI:10.1146/annurev-phyto-011014-015624 · 11.00 Impact Factor