AVRXa10 protein is in the cytoplasm of Xanthomonas oryzae pv. oryzae

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. Polyclonal antibodies raised against purified AVRXa10 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 fractionation and immunoelectronmicroscopy analysis was used to demonstrate that AVRXa10 was located in the cytoplasm of X. o. pv. oryzae cells when grown in planta or in culture medium.