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Sci Adv. 2015 Jul 24;1(6):e1500245. doi: 10.1126/sciadv.1500245. eCollection 2015 Jul.

The rice immune receptor XA21 recognizes a tyrosine-sulfated protein from a Gram-negative bacterium.

Author information

1
Department of Plant Pathology and the Genome Center, University of California, Davis, Davis, CA 95616, USA. ; Joint BioEnergy Institute and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
2
Department of Plant Pathology and the Genome Center, University of California, Davis, Davis, CA 95616, USA. ; Joint BioEnergy Institute and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. ; The Australian National University, Research School of Biology, Acton ACT 2601, Australia.
3
Department of Plant Pathology and the Genome Center, University of California, Davis, Davis, CA 95616, USA.
4
Centre for Plant Molecular Biology, University of Tübingen, 72074 Tübingen, Germany.
5
Joint BioEnergy Institute and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
6
Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92697, USA.
7
Interfaculty Institute of Biochemistry, University of Tübingen, 72074 Tübingen, Germany.
8
Council of Scientific & Industrial Research (CSIR)-Institute of Microbial Technology, Chandigarh 160036, India.
9
CSIR-Centre for Cellular and Molecular Biology, Hyderabad 500007, India.
10
Department of Biomedical Engineering, University of California, Irvine, Irvine, CA 92697, USA. ; Department of Chemistry, University of California, Irvine, Irvine, CA 92697, USA.
11
Department of Chemistry, University of Texas at Austin, Austin, TX 78712, USA.

Abstract

Surveillance of the extracellular environment by immune receptors is of central importance to eukaryotic survival. The rice receptor kinase XA21, which confers robust resistance to most strains of the Gram-negative bacterium Xanthomonas oryzae pv. oryzae (Xoo), is representative of a large class of cell surface immune receptors in plants and animals. We report the identification of a previously undescribed Xoo protein, called RaxX, which is required for activation of XA21-mediated immunity. Xoo strains that lack RaxX, or carry mutations in the single RaxX tyrosine residue (Y41), are able to evade XA21-mediated immunity. Y41 of RaxX is sulfated by the prokaryotic tyrosine sulfotransferase RaxST. Sulfated, but not nonsulfated, RaxX triggers hallmarks of the plant immune response in an XA21-dependent manner. A sulfated, 21-amino acid synthetic RaxX peptide (RaxX21-sY) is sufficient for this activity. Xoo field isolates that overcome XA21-mediated immunity encode an alternate raxX allele, suggesting that coevolutionary interactions between host and pathogen contribute to RaxX diversification. RaxX is highly conserved in many plant pathogenic Xanthomonas species. The new insights gained from the discovery and characterization of the sulfated protein, RaxX, can be applied to the development of resistant crop varieties and therapeutic reagents that have the potential to block microbial infection of both plants and animals.

KEYWORDS:

Bacteria; Rice; immune receptors

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