Xanthomonas oryzae pv. oryzae AvrXA21 Activity Is Dependent on a Type One Secretion System, Is Regulated by a Two-Component Regulatory System that Responds to Cell Population Density, and Is Conserved in Other Xanthomonas spp.
The rice pathogen recognition receptor, XA21, confers resistance to Xanthomonas oryzae pv. oryzae (Xoo) strains expressing the pathogen-associated molecule, AvrXA21. XA21 codes for a receptor-like kinase consisting of an extracellular leucine rich repeat (LRR) domain, a transmembrane domain, and a cytoplasmic kinase domain (Ronald et al., 1992; Song et al., 1995). We show that AvrXA21 activity requires the presence of rax (required for AvrXA21) A, raxB, and raxC genes that encode components of a type one secretion system (TOSS). In contrast, an hrpC- strain deficient in type three secretion maintains AvrXA21 activity. Xanthomonas campestris pv. campestris (Xcc) can express AvrXA21 activity if raxST, encoding a putative sulfotransferase, and raxA are provided in trans. Expression of rax genes is dependent on population density and other functioning rax genes, suggesting that AvrXA21 is involved in quorum sensing and that the AvrXA21 pathogen-associated molecule represents an entirely new class of Gramnegative bacterial signaling molecules. We discuss the implications of these results for models of plant innate immunity.
Here, we provide a brief overview of some of the major concepts and molecular features of plant and animal innate immune system perception. We then describe new results from our studies of the XA21–AvrXA21 interaction and discuss how these results call for some modifications in the way we think about plant innate immunity strategies.
KeywordsTyrosine Adenosine Bacillus Oligomerization Arginine
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- Brueggeman, R., Rostoks, N., Kudrna, D., Kilian, A., Han, F., Chen, J., Druka, A., Steffenson, B., and Kleinhofs, A., 2002, The barley stem rust-resistance gene Rpg1 is a novel disease-resistance gene with homology to receptor kinases, Proc. Nat. Acad. Sci. USA 99:9328–9333.PubMedCrossRefGoogle Scholar
- Dodds, P.N., Lawrence, G.J., Catanzariti, A.M., Teh, T., Wang, C.I., Ayliffe, M.A., Kobe, B., and Ellis, J.G., 2006, Direct protein interaction underlies gene-for-gene specificity and coevolution of the flax resistance genes and flax rust avirulence genes, Proc. Nat. Acad. Sci. USA 103:8888–8893.PubMedCrossRefGoogle Scholar
- Goes da Silva, F., Shen, Y., Dardick, C., Burdman, S., Yadav, R., Sharma, P., and Ronald, P., 2004, Bacterial genes involved in type I secretion and sulfation are required to elicit the rice Xa21-mediated innate immune response, MPMI 17:593–601.Google Scholar
- Jha, G., Rajeshwari, R., and Sonti, R.V., 2005, Bacterial type two secretion system secreted proteins: double edged swords for plant pathogens, Mol. Plant In. 18:891–898.Google Scholar
- Kauffman, H.E., Reddy, A.P.K., Hsieh, S.P.Y., and Merca, S.D., 1973. An improved technique for evaluating resistance of rice varieties to Xanthomonas oryzae, Plant Dis. Rep. 57:537–541.Google Scholar
- Ramos, H.C., Rumbo, M., and Sirard, J.C., 2004 Bacterial flagellins: mediators of pathogenicity and host immune responses in mucosa, Trends Microbiol. 12:509–517.Google Scholar
- Szurek, B., Marois, E., Bonas, U., and Van den Ackerveken, G., 2001, Eukaryotic features of the Xanthomonas type III effector AvrBs3: protein domains involved in transcriptional activation and the interaction with nuclear import receptors from pepper, Plant J. 26:523–534.PubMedCrossRefGoogle Scholar
- Teplitski, M., Chen, H., Rajamani, S., Gao, M., Merighi, M., Sayre, R.T., Robinson, J.B., Rolfe, B.G., and Bauer, W.D., 2004, Chlamydomonas reinhardtii secretes compounds that mimic bacterial signals and interfere with quorum sensing regulation in bacteria, Plant Physiol. 134:137–146.PubMedCrossRefGoogle Scholar
- Wang, G.L., Ruan, D.L., Song, W.Y., Sideris, S., Chen, L., Pi, L.Y., Zhang, S., Zhang, Z., Fauquet, C., Gaut, B.S., Whalen, M.C., and Ronald, P.C., 1998, Xa21D encodes a receptor-like molecule with a leucine-rich repeat domain that determines race-specific recognition and is subject to adaptive evolution, Plant Cell 10:765–779.PubMedCrossRefGoogle Scholar