title: Suppression ofXo1-Mediated Disease Resistance in Rice by a Truncated, Non-DNA-Binding TAL Effector ofXanthomonas oryzae.
abstract: Delivered into plant cells by type III secretion from pathogenicXanthomonasspecies, TAL (transcription activator-like) effectors are nuclear-localized, DNA-binding proteins that directly activate specific host genes. Targets include genes important for disease, genes that confer resistance, and genes inconsequential to the host-pathogen interaction. TAL effector specificity is encoded by polymorphic repeats of 33-35 amino acids that interact one-to-one with nucleotides in the recognition site. Activity depends also on N-terminal sequences important for DNA binding and C-terminal nuclear localization signals (NLS) and an acidic activation domain (AD). Coding sequences missing much of the N- and C-terminal regions due to conserved, in-frame deletions are present and annotated as pseudogenes in sequenced strains ofXanthomonas oryzaepv. oryzicola (Xoc) and pv. oryzae (Xoo), which cause bacterial leaf streak and bacterial blight of rice, respectively. Here we provide evidence that these sequences encode proteins we call "truncTALEs," for "truncated TAL effectors." We show that truncTALE Tal2h of Xoc strain BLS256, and by correlation truncTALEs in other strains, specifically suppress resistance mediated by theXo1locus recently described in the heirloom rice variety Carolina Gold.Xo1-mediated resistance is triggered by different TAL effectors from diverseX. oryzaestrains, irrespective of their DNA binding specificity, and does not require the AD. This implies a direct protein-protein rather than protein-DNA interaction. Similarly, truncTALEs exhibit diverse predicted DNA recognition specificities. And,in vitro, Tal2h did not bind any of several potential recognition sites. Further, a single candidate NLS sequence in Tal2h was dispensable for resistance suppression. Many truncTALEs have one 28 aa repeat, a length not observed previously. Tested in an engineered TAL effector, this repeat required a single base pair deletion in the DNA, suggesting that it or a neighbor disengages. The presence of the 28 aa repeat, however, was not required for resistance suppression. TruncTALEs expand the paradigm for TAL effector-mediated effects on plants. We propose that Tal2h and other truncTALEs act as dominant negative ligands for an immune receptor encoded by theXo1locus, likely a nucleotide binding, leucine-rich repeat protein. Understanding truncTALE function and distribution will inform strategies for disease control.
authors: Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors: Andrew C
authors: AC
authors: Read
authors: Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors: Fabio C
authors: FC
authors: Rinaldi
authors: Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors: Mathilde
authors: M
authors: Hutin
authors: Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell UniversityIthaca, NY, USA; State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi UniversityNanning, China.
authors: Yong-Qiang
authors: YQ
authors: He
authors: Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station New Haven, CT, USA.
authors: Lindsay R
authors: LR
authors: Triplett
authors: Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University Ithaca, NY, USA.
authors: Adam J
authors: AJ
authors: Bogdanove
keywords: NLR protein; Xanthomonas oryzae; bacterial blight of rice; bacterial leaf streak of rice; defense suppression; plant disease resistance; protein-protein interaction; transcription activator-like effector