A Primary Study On Resistance Mechanism Of Rice Blast Resistance Gene Pi36

Rice blast is one of the most destructive diseases of rice (Oryza sativa L.), it is widely distributed with great harm, and has plagued the rice production for long times. Compared with the high cost and heavy pollution of chemical prevention, the use of resistant cultivars is the most effective and securative strategy against blast. One of the objectives for the breeding against blast is excavating and utilizing of the new resistant source with broad-spectrum resistance. Through the map-based cloning strategy, a new blast resistance gene, Pi36, was cloned. In this paper the resistance mechanism mediated by Pi36 is further carried out. The main results are as follows:1. A over-expression vector of Pi36 was constructed and a number of transgenic plants were obtained by Agrobacterium-mediated transformation to the susceptible acceptor cultivar Lijiangxintuanheigu (LTH). The blast resistance of T1 transgenic plants was confirmed by artificial inoculation of blast fungus. The result of trypan blue staining showed that cell death occurred in the leaves of transgenic plants after blast fungus infection, which resulted in the blast resistance of transgenic plants. In addition, the results from the expression patterns of the defense-associated genes in transgenic plants suggested that Pi36-mediated blast resistance may be related to the salicylic acid signaling pathway.2. MAPK genes have an important role in signal transduction in plant defense responses. In this study, the expression profiles of 17 OsMAPK genes in Pi36- mediated resistance were investigated using real-time PCR. The results showed that OsMAPK2, OsMAPK4, OsMAPK8 and OsMAPK15 were upregulated in the resistant cultivar but not in the susceptible cultivar. This suggested that the 4 MAPK genes may be involved in Pi36-mediated defense.3. In order to study the function of MAPK genes involved in Pi36-mediated defense, the over-expression and RNAi vectors of OsMAPK2 were constructed. Using the resistant cultivar Kasalath and susceptible cultivar LTH as the acceptor for the Agrobacterium-mediated transformation, a number of positive transgenic plants were obtained. The result of RT-PCR showed that the expression of OsMAPK2 was downregulated in the RNAi transgenic T0 plants.