Proteins involved in host-pathogen interactions (Xanthomonas oryzae pv. oryzae vs. rice)

AVRXa10 from Xanthomonas oryzae pv. oryzae and a cationic peroxidase (PO-C1) and phospholipase D (PLD) proteins from rice were localized by the use of immunoprobes to characterize the intimate relationships between the pathogen and host.;PO-C1 which is induced in resistant interactions between the vascular pathogen X. o. pv. oryzae and rice was purified. Polyclonal antibodies were raised to an eleven amino acid oligopeptide (POC1a). The anti-POC1a antibodies reacted with a protein of the same mobility as PO-C1. Immunoelectron-microscopy was used to demonstrate that PO-C1 accumulated within the apoplast of mesophyll cells, and within the cell walls and vessel lumen of xylem elements of plants undergoing resistant interactions.;PLD, which hydrolyzes phospholipids, was examined in 10-day-old rice leaves undergoing susceptible or resistant interactions with X. o. pv. oryzae. Differential changes were observed in PLD mRNA and three PLD variants in rice during resistant interactions with X. o. pv. oryzae. The location of PLD was determined by transmission and scanning electron microscopy after immunogold labeling. In cells undergoing a susceptible response, PLD was uniformly distributed along the mesophyll cell plasma membrane at 3 and 24 hr after inoculation. However, 24 hr after bacterial challenge in resistant interactions, PLD was clustered preferentially in membranes adjacent to bacterial cells. These studies indicate complex mechanisms for the regulation and change in distribution of PLD during interactions with pathogens.;AVRXa10 from X. o. pv. oryzae was tagged with a unique hydrophilic octapeptide (FLAG). 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 did not elicit a HR 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. Biochemical fractionation and immunoelectron-microscopy 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.