AVRXalO Protein is in the Cytoplasm of Xanthomonas oryzae pv. oryza . Scott A. Young. Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan, KS 66506-5502 U.S.A. Frank F. White (1), Christopher M. Hopkins (2), and Jan E. Leach (1). (1) Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan, KS 66506-5502 U.S.A. (2) Department of Environmental Science, Policy, and Management, Berkeley, CA 94720 U.S.A. MPMI 7:799-804. Accepted 18 July 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society 1994.

AVRXa10 from Xanthomonas oryzae pv. oryzae was tagged with a unique hydrophilic octapeptide (FLAG) to permit antibody-mediated identification and purification of the gene product. X. o. pv. oryzae that produced tagged AVRXa10 elicited a hypersensitive response (HR) on rice cultivars containing the resistance gene Xa-10, but not on cultivars lacking Xa-10. The tagged AVRXa10 protein purified from Escherichia coli or X. o. pv. oryzae did not elicit a hypersensitive response in rice with the Xa-10 resistance gene. Anti-FLAG monoclonal antibodies reacted with a 119-kDa protein in both E. coli and X. o. pv. oryzae cells expressing the tagged avrXa10 gene. Polyclo-nal antibodies raised against purified AVRXalO protein reacted with the 119-kDa protein and several additional proteins from X. o. pv. oryzae, which probably are the products of genes related to avrXa10. Biochemical frac-tionation and immunoelectronmicroscopy analysis was used to demonstrate that AVRXalO was located in the cytoplasm of X. o. pv. oryzae cells when grown in planta or in culture medium.