Plant Genome IV Conference Plant Genome IV Conference
A family of genes that are involved in the induction of resistance in rice were cloned from the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae. Two of the genes, avrXa7 and avrXa10, are similar in structure to avrBs3, an avirulence (avr) gene from X. campestris pv. vesicatoria. The central domains of avrXa7 and avrXa10 contain 25.5 and 17.5 copies, respectively, of a near perfect 102 bp directly repeated sequence. The protein products of the avr genes were detected only in the bacterial cytoplasm, suggesting the proteins are not the direct elicitors of resistance. Experiments are in progress to identify bacterial proteins that interact with the avr gene products and the bacterial elicitors of resistance. Bacterial strains isogenic for the avr genes and rice cultivars near-isogenic for the corresponding resistance genes were used to study resistant interactions. Resistance in rice is characterized by: (a) an increase in peroxidases in the xylem vessels, the site of bacterial multiplication and spread, (b) a novel change in membrane distribution patterns for rice phospholipase D in mesophyll cells adjacent to bacterial cells, (c) lignin deposition, (d) host cell death, and (e) a decrease in the rate of bacterial multiplication.