| 研究概要 |
Currently, there are many reports of defence response pathways that are induced after pathogen attack on plants. However, very few of those reports are on host-parasitic plants interactions and in fact where available, they are contradictory. Reports have shown that the most important defence response pathways in plants are the salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) pathways. I am studying the interaction between rice and a root parasite called Striga hermonthica. The aim of the project is to elucidate host defence response mechanisms. Towards this goal, I infected Koshihikari and Nipponbare rice roots with Striga. Koshihikari is susceptible to Striga whereas Nipponbare is resistant. The results showed that the expression of SA- and JA-related genes was induced after infection suggesting that defence response against Striga in rice roots involved induction of both SA and JA pathways. We could not detect significant changes in gene expression of ET-related genes. Furt
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hermore, foliar application of benzothiadiazole (BTH) an SA analog, and jasmonic acid (JA) induced a systemic defence response that enhanced Striga resistance especially in Striga-susceptible Koshihikari plants. This enhanced resistance was associated with very few, small Striga seedlings attaching to host roots. These experiments were repeated using rice plants deficient in SA and JA biosynthesis. The results showed that the post-attachment resistance of SA biosynthesis mutants was comparable to that of Striga resistant Nipponbare. On the other hand, the JA biosynthesis mutation enhanced susceptibility to Striga infection and that the phenotype could be rescued by foliar application of JA. Even though JA enhanced resistance to Striga infection, its application in field conditions has inherent difficulties because it might induce unwanted reactions such as limitation of growth in plants. One of the chemicals that have been reported to mimic JA without inducing unwanted reactions in plants is coronatine. We conducted gene expression analysis, measured post-attachment resistance and quantified hormone levels in rice plants whose leaves had been sprayed with coronatine before infecting with Striga. The results showed that the effect of coronatine on the resistance of rice roots was comparable to that of JA. Furthermore, we also found out that application of coronatine inhibited the accumulation of SA in Striga infected rice roots suggesting that there was an antagonistic interaction. 隠す
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