Submitted to: Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2006
Publication Date: 9/1/2006
Citation: Lee, J., Bricker, T.R., Lefevre, M., Pinson, S.R., Oard, J.H. 2006. Proteomic and genetic approaches to identifying defense-related proteins in rice challenged with the fungal pathogen Rhizoctonia solani. Molecular Plant Pathology 7(5):405-416. Interpretive Summary: For a host organism (animal or plant) to fight off a disease-causing organism, the host first chemically 'recognizes' the foreign organism as an invader, then triggers the appropriate microbe-fighting response to repel or kill the invading pathogen. The response of rice plants to Pyricularia oryzae which causes blast disease has been much studied. The rice plant prevents spread of P. oryzae by rapidly killing the rice cells in and near the point of infection, a host response known as hypersensitivity. Rice responds very differently, however, to Sheath Blight disease which is caused by the fungus Rhizoctonia solani. Plant cells around the infection site also die, but now they are killed by a pathogen produced toxin rather than from the plant's self-defense response. Resistant rice shows less pathogen growth and less cell death than do susceptible plants. Scientists do not yet know at a biochemical level why some rice varieties exhibit more resistance than others to Sheath Blight. They might prevent pathogen infection or growth in some way, or they might detoxify the toxins. Most likely, the most resistant plants trigger a series of multiple protective responses. The objective of this study was to compare the proteins and genes produced or expressed by resistant versus susceptible rice plants in response to infection by R. solani in order to identify those putatively associated with resistance to this disease. Seven proteins were expressed more after inoculation by susceptible and resistant plants. Six out of the seven proteins showed similarity with the structures of proteins and genes reported in the literature as having antifungal, photosynthetic, and protein-digesting (i.e. toxin deactivation or digestion of pathogen components) activities. Additionally, the resistant line increased production of fourteen proteins that were not induced in the susceptible rice. Eleven of these fourteen proteins showed molecular similarity with proteins identified elsewhere as having functions relating to antifungal activity, signal transduction, energy metabolism, photosynthesis, proteolysis, and antioxidation . Four of the proteins expressed preferentially by resistant rice were found to be located in rice chromosomal regions previously reported to contain sheath blight resistance genes. The proteomic and genetic results from this study indicate a complex response of rice to challenge by R. solani that involves simultaneous induction of proteins from multiple defense pathways. The induction of 3-'- hydroxysteroid dehydrogenase/isomerase was detected for the first time in resistant rice plants after pathogen challenge, suggesting a defensive role of this enzyme in rice against attack by R. solani.
Technical Abstract: Sheath blight, caused by the fungus Rhizoctonia solani, is a major disease of rice worldwide, but little is known about the host response to infection. The objective of this study was to identify proteins and DNA markers in resistant and susceptible rice associated with response to infection by R. solani. Replicated two-dimensional polyacrylamide gel electrophoresis experiments were conducted to detect proteins differentially expressed under inoculated and non-inoculated conditions. Tandem mass spectra analysis using electrospray ionization quadrupole-time of flight mass spectrometry (ESI Q-TOF MS) was carried out for protein identification with the NCBI nonredundant protein database. Seven proteins were up-regulated after inoculation in both susceptible and resistant plants. Six out of the seven proteins were identified with presumed antifungal, photosynthetic, and proteolytic activities. An additional fourteen proteins were detected in the response of the resistant line. Eleven of the fourteen proteins were identified with presumed functions relating to antifungal activity, signal transduction, energy metabolism, photosynthesis, molecular chaperone, proteolysis, and antioxidation. The induction of 3-'- hydroxysteroid dehydrogenase/isomerase was detected for the first time in resistant rice plants after pathogen challenge, suggesting a defensive role of this enzyme in rice against attack by R. solani. The chromosomal locations of four induced proteins were found to be in close physical proximity to genetic markers for sheath blight resistance in two genetic mapping populations. The proteomic and genetic results from this study indicate a complex response of rice to challenge by R. solani that involves simultaneous induction of proteins from multiple defense pathways.