| Adzuki bean rust,caused by the fungus Uromyces vignae,is one of the most serious diseases that seriously affects the yield and quality in adzuki bean?Vigna angularis?production.Adzuki bean rust management mainly depends on the application of fungicide,due to most of the cultivar used presently are susceptible to U.vignae.However,long-term use of chemical reagents might be drawback sisadvantages including fungicide resistance,drug residues,and environmental pollution.Therefore,application of exogenous plant hormones to inducing immunity of plants against phytopathogens were considered to be an effective and safe disease management stratiges.In addition,genes involved in ethylene?ET?biosynthesis and ET signaling pathway were significantly up-regulated at 24 h post inoculation?hpi?in the resistant cultivarVaHR136.Tothisend,theethylenebiosynthesisprecursor1-aminocyclopropanecarboxylic acid?ACC?was used as resistance inducing agent.Subsequently,the effect and mechanism of inducing rust resistance of adzuki bean were investigated.1.Inoculation with urediospora of U.vignae 2 days after spraying of ACC at different concentration.The disease index of different treatments were investigated,and the results showed that 0.25 mg·mL-1 ACC can significantly increas the rust resistance of adzuki bean.Compared with sterile water treatment,the disease index decreased by 45.06%.The urediospora germination test showed that different concentrations of ACC had no significant inhibitory effect on urediospora germination.The results indicated that ACC can induce rust resistance of adzuki bean,and the suitable concentration was 0.25 mg·mL-1.2.ACC treatment can not only induce rust resistance of adzuki bean,but also cause ethylene"triple reactions"including top hook,leaf curl and plant height decrease.Expression analysis of ethylene biosynthesis?MPK3,MPK6?and signaling pathway related genes?EIN2,EIN3,ERF2,ERF5?after ACC treatment by qRT-PCR.The results showed that MPK3 and MPK6 were up-regulated after ACC treatment compared with sterile water treatment.Ethylene signaling pathway core positive regulators EIN2 and EIN3 were significantly up-regulated 48 h after ACC treatment.And activate the downstream transcription factors ERF2 and ERF5 up-regulated.It indicated that the accumulation of endogenous ethylene content in adzuki bean was promoted after ACC treatment and activated ethylene signaling pathway,which resulting in a"triple reactions"of adzuki bean plants.3.In order to further explore the role of ethylene signaling pathway in ACC-induced resistance.The present study analyzed the expression of EIN2,EIN3,ERF2 and ERF5 after different times of inoculation that pretreated with ACC.Results showed that the ethylene positive regulators EIN2 and EIN3 were significantly up-regulated in the early stage of infection?0-24 h?in comparison with control.At the late stage of infection?after 48 h?,the expression level decreased significantly.The ethylene signaling pathway inhibitor 1-MCP co-processing with ACC and then inoculated with U.vignae,the investigation of plant growth and resistance phenotype showed that 1-MCP inhibited the triple reaction of adzuki bean but not inhibited the rust resistance that induced by ACC treated.The above results indicated that ACC-induced rust resistance is not completely dependent on the activation of ethylene signaling pathway.4.In order to preliminarily determine the mechanism of ACC-induced rust resistance.The expressions of defense-related genes such as PR2,PR4 and NPR1 were analyzed at different time points pretreated with ACC by using qRT-PCR.Compared with the control,the expression levels of PR2,PR4 and NPR1 peaked at 24 h after inoculation,and then decreased but the expression level is still significantly higher than the control.Furthermore,the activity of chitinase and?-1,3 glucanase assay showed that chitinase activity was significantly increased 48h after inoculation that pretreated with ACC,but the?-1,3 glucanase activity was not significantly different with control.The results indicating that activation of the defense-related genes of PR2,PR4 and NPR1,and significantly increased the activity of chitinase might be play important roles in the induced resistance of ACC. |
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