Mechanism of resistance to tobacco gray mold induced by the active metabolite of Streptomyces roseoflavus

【Objective】To study the mechanism of resistance to tobacco gray mold induced by the active metabolite Roflamycoin and Men-myco-A（R&M）of Streptomyces roseoflavus Men-myco-93-63 under greenhouse conditions，so as to provide theoretical basis for the ecofriendly use of R&M to prevent and control tobacco gray mold.【Method】Eighty mg/L R&M was injected to 4-5 leaf stage of Nicotiana benthamiana to conduct hypersensitive response（HR）staining verification and 100 mg/L R&M was injected to 4-5 leaf stage of N.benthamiana to get expression of the disease resistance marker gene hsr203J respectively to verify the induced disease resistance of R&M.Changes of catalase（CAT） activity，lipoxygenase（LOX）activity and content of hydrogen peroxide（H₂O₂），a defense-related substance，in non-pharmaceutically treated tobacco leaves of N.benthamiana were detected by kits（treatments of 80 mg/L R&M spray and water treatment）.Quantitative real-time PCR（qRT-PCR）technology was used to detect changes of relative expression of lignin synthesis-related gene PAL and pathogenesis-related protein（PR）genes PR1 and PR5 after tobacco treatments（treatment 1，80 mg/L R&M solution for root treatment for 2 d，friction inoculation with Botrytis cinerea spore suspension on the upper third leaves；treatment 2，root irrigation with water for 2 d，friction inoculation with water on the upper third leaves）.【Result】Catalase（CAT）activity in tobacco leaves gradually increased after induction treatment with 80 mg/L R&M；while lipoxygenase（LOX）activity increased significantly after 3 d（P<0.05，the same below），and both reached the highest on 7 d.H₂O₂ content increased rapidly on the 1 d and then decreased.Relative expression of PAL gene significantly was up-regulated after 24 h，which was 25.37 folds of that of CK.Relative expression of PR genes，PR1 and PR5，reached the highest at 24 h and 72 h respectively，which were 11.23 times and 11.17 times of those of the CK.【Conclusion】R&M enhances disease resistance of tobacco plants through increasing the activity of related defense enzymes in tobacco leaves，coordinating the level of active oxygen and increasing the expression level of disease resistance-related genes.R&M，an active metabolite produced by S.roseoflavus Men-myco-93-63，is potential to be elicitor of disease of plant and expected to be applied in ecofriendly prevention and control of diseases such as gray mold.