Pathogenesis-related Proteins Were Induced In Rice Bacterial Blight Resistant Gene Xa21-mediated Interactions With Xanthomonas Oryzae Pv. Oryzae

Rice (Oryza sativa) is a very important crop in the world. Rice bacterial blight is one of the most important rice diseases. Rice bacterial blight was caused by the bacterial pathogen, Xanthomonas oryzae pv. oryzae (Xoo). It can reduce the yield, and it can even result in the lost of harvest. Xa21, which is a broad-spectrum resistance gene of rice bacterial blight, encodes a receptor-like kinase XA21. To study the resistance mechanism of Xa21 not only has great theoretical significance, but also has important practical value.Pathogenesis-related proteins (PRs) have been defined as the proteins and their homologues induced by pathogens. They are enzymes such as phenylalanine ammonia-lyase (PAL), peroxidase, and polyphenoloxidase, which normally exist in the plant. The expression of these proteins will be increased after serious infection. Pathogens, insects, nematodes and herbivores can all induced the expression of PRs. PRs were classified as 17 families.The function of PR-1 family is still unknown as well as PR-17. PR-2 hasβ-1, 3-glucanase activity. Chitinase activity was detected in PR-3, PR-4, PR-8 and PR-11. PR-4 is chitin-binding protein and PR-8 is lysozyme. Proteinase, peroxidase and ribonuclease activities were established in PR-7, PR-9 and PR-10. PR-6 was assigned proteinase-inhibitory properties. Membrane–permeabilizing functions are characteristic of defensins, thiols and lipid-transfer proteins (LTPs), referred to as PR-12, PR-13 and PR-14, respectively, and of osmotins and thaumatin-like proteins PR-5. Multiple enzymatic, structural and receptor functions are detected in"do-all"germins and germin-like proteins referred to as PR-15 and PR-16, respectively. As the downstream defence gene, pathogenesis-related gene exists in a wide range of different plants. The expression of PRs is induced by pathogens, but is also mediated by the upstream resistance gene.We slected OsPR1a, OsPR1b and OsPR10a as the objects of our study, in order to reveal the relationship between Xa21 and PRs, which can contribute to clarify the resistance mechanism of rice. We cloned and expressed them in E.coli and prepared the antibodies. Western-blot approach was used to examine the expression differences of PRs (OsPR1a, OsPR1b and OsPR10a) in four kinds of rice materials, which are resistant (R), susceptible (SR-), susceptible (SAvr-) and mock (M). After analysis we found that, (1) the expression level of PRs is induced higher in resistant response with Xa21-mediated(R) than in susceptible response without (SR-). (2)The Xa21 locus is required for higher induction of PRs in incompatible interaction (R) than compatible interaction(SR-). (3)The expression of OsPR1a, OsPR1b and OsPR10a proteins between SR- and SAvr- reaction have no obvious difference. These means that, (1) When the resistance gene and the avirulence genes of plant pathogens can recognize each other(R), the expression of PRs could be up-regulated by Xa21. (2) When the avirulence genes of plant pathogens can not recognize each other (SAvr-), the expression of PRs could not be mediated by Xa21, which has no difference with the susceptible interaction(SR-).