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Title: Release of elicitors from rice blast spores under the action of reactive oxygen species

Author
item ZAKHARENKOVA, TATIANA - Russian Institute Of Phytopathology
item AVERYANOV, ANDREY - Russian Institute Of Phytopathology
item PASECHNIK, TATIANA - Russian Institute Of Phytopathology
item LAPIKOVA, VERA - Russian Institute Of Phytopathology
item Baker, Con

Submitted to: Russian Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2010
Publication Date: 12/1/2010
Citation: Zakharenkova, T.S., Averyanov, A.A., Pasechnik, T.D., Lapikova, V.P., Baker, C.J. 2010. Release of elicitors from rice blast spores under the action of reactive oxygen species. Russian Journal of Plant Physiology. 57:615-619.

Interpretive Summary: Rice Blast disease of rice causes major losses for farmers each year. This disease starts by the germination of the fungal spore on the leaf surface. By learning to disrupt critical mechanisms that are involved in spore germination we could reduce the amount of disease. In this study a new mechanism involving the production of elicitors by the germinating fungal spore is described. These elicitors cause resistant reactions on cultivars that are resistant to the Rice Blast fungus. This elicitation is promoted by reactive oxygen species produced by both the fungal spore and the rice plant. If the production of reactive oxygen species on the leaf surface can be stimulated, this may help reduce disease. This information will be of use to plant scientists who are devising new strategies to improve disease resistance in plants.

Technical Abstract: The effects of reactive oxygen species (ROS) on secretion of hypothesized elicitors from spores of rice blast causal fungus Magnaporthe grisea were studied. For spore exposure to exogenous ROS, they were germinated for 5 h in 50 µM H2O2 followed by addition of catalase E.C. 1.11.1.6 (to decompose peroxide) and boiling spore germination fluid (to inactivate catalase). The resulting diffusate applied to rice (Oryza sativa) leaves caused necrosis and increased superoxide (O2-) production by leaves. Both effects took place on rice cultivar that is resistant but not susceptible to the fungal strain. The susceptible cultivar did not acquire resistance to challenge with fungal spores performed one day post treatment. Spore diffusate separation showed that both low- and high-molecular weight compounds (lower and higher than 3 kDa) were required simultaneously to induce O2- production by leaves. Diffusates of spores germinated in water exhibited smaller O2- enhancing activity than diffusates of spores germinated in H2O2. This effect was abolished by catalase or superoxide dismutase (SOD)(E.C. 1.15.1.1) added initially to spore suspensions. It is suggested that germinating blast spores are able to secrete elicitors, and this ability depends on ROS formed by spores. The surplus ROS from the host or produced by the stressed parasite may increase the elicitor release. Thus, the phenomenon reported may be involved in the disease resistance mechanism.