Expression Of Salicylate-5-hydroxylase Gene And P35 Gene Affect Plant Disease Resistance And Studies On The Possible Mechanisms

This thesis is about the transformation of exogenous genes into tobacco and the subsequent effects on plant disease resistances, and includes three chapters:Chapter one is a literature overview of the routes and mechanisms of plant disease resistance, with the emphasize on the roles of the signal moleculars SA,JA,ET in the signal transduction pathways, and the interactions of the related genes in plant defense signaling pathways. The possible role of the new signal molecuar gentisate acid (GA ) is discussed, and the effects of suppressing plant cell death by expressing the p35 gene in plant disease resistance is also outlined.Chapter two is about the expression of salicylate -5-hydroxylase gene in tobacco to study the effects of the conversion of salicylic acid to gentisate acid on plant disease resistance. nagAaGHAb gene from Ralstonia U2 strain was cloned into plant expression vector, Agrobacterium-mediated transformation of tobacco was carried out and kanamycin resistant plants were obtained. T1 seeds were germinated on MS0 medium containing 50 mg/L kanamycin and the transformants were confirmed by PCR and RT-PCR. T1 seeds with kanamycin segregation ratio of 3:1 were germinated on medium containing different concentrations of salicylic acid. Seedling growth, fresh weight and root length of control and transgenic tobacco were analized and the transgenic plants showed more resistance to SA and grow better than the control plants. Inoculation of transgenic tobacco leaves with TMV showed attenuated hypersensitive response. RT-PCR and Western-blot analysis showed S5H gene expression reduced the transcription of PR-1 gene. Diaminobenzidine (DAB) staining showed that S5H gene expression had no effect on the accumulation of H2O2. At different times after inoculation with TMV, SA content of transgenic and control leaf tissues were measured by HPLC, and the result showed that...