外源水杨酸诱导香蕉苯丙烷类代谢提高对枯萎病抗性

由尖孢镰刀菌古巴专化型热带4号生理小种（Fusarium oxysporum f. sp. cubense tropical race 4, TR4）引起的香蕉枯萎病严重阻碍我国香蕉产业的绿色可持续发展。外源水杨酸（SA）处理能诱导香蕉体内SA合成及信号传导途径关键酶基因上调表达,激活香蕉植株内系统获得抗性,增强对各种生物和非生物胁迫的抵抗能力,在此基础上,本研究对香蕉感病品种‘巴西蕉’和抗病品种‘农科1号’进行SA诱导处理,随后接种TR4,结果显示2个品种的病情指数均降低。为了进一步探究水杨酸信号途径下游的苯丙烷类途径在SA诱导的香蕉植株抗病过程中的作用,本研究运用实时荧光定量PCR技术（RT-qPCR）,对SA处理的感病品种‘巴西蕉’和抗病品种‘农科1号’中苯丙烷类途径关键基因的表达情况进行分析,结果发现分支途径中常规苯丙烷类途径关键酶基因C4H和4CL、木质素合成途径关键酶基因CAD和CCoAOMT、黄酮类物质生物合成途径关键酶基因CHS和CHI,对SA处理和TR4接种均有响应。在仅接种TR4的情况下,‘巴西蕉’相关基因主要表现为显著下调表达,而‘农科1号’相关基因主要表现为上调表达;仅用SA处理时,2个品种的C4H和4CL被诱导上调表达;SA处理并接种TR4,2个品种C4H和4CL依然保持上调表达的趋势,变化幅度在‘农科1号’中偏高;‘巴西蕉’CAD经SA诱导上调表达,但在接种TR4后,CAD相对表达量降低,而‘农科1号’CAD被SA诱导显著上调表达,SA和TR4共同作用下,表达水平亦显著升高;‘巴西蕉’CCoAOMT被TR4诱导显著上调表达,在SA处理并接种TR4的‘巴西蕉’植株中也表现为上调表达,‘农科1号’CCoAOMT在SA处理或SA、TR4共同作用下表现为强烈上调表达;CHS和CHI在SA处理的2个品种中主要表现为上调表达,SA和TR4双重作用下,依然表现为上调表达。结果表明外源SA处理可诱导感病和耐病香蕉根组织中苯丙烷类途径关键酶基因上调表达,该途径在SA诱导的香蕉抗枯萎病过程中起着重要作用。

Exogenous Salicylic Acid Induced Phenylpropane Metabolism in Banana to Improve the Resistance Against Fusarium Wilt

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) seriously hinders the green and sustainable development of banana industry in China. Exogenous salicylic acid (SA) treatment can induce the key enzyme genes up-regulation in SA synthesis and signaling pathway and further activate systemic resistance in bananas against a variety of biotic and abiotic stresses. In this research, the susceptible banana cultivar ‘Brazilian’ and resistant banana cultivar ‘Nongke No.1’ after treated with SA were inoculated with TR4. The results showed that the disease index of the two cultivars treated with SA decreased when it was compared with the SA-untreated control. In order to explore the role of phenylpropanoid pathway located downstream of SA synthesis and signaling pathway during banana resistance induced by exogenous SA against Fusarium wilt, the key genes’ expression of phenylpropanoid pathway in susceptible and resistant banana cultivars treated with SA was analyzed by fluorescence quantitative PCR (RT -qPCR). It was found that the key genes C4H and 4CL in general phenylpropanoid pathway were responsive to both SA induction and TR4 inoculation. The same was true for CAD and CCoAOMT in lignin biosynthesis pathway and CHS and CHI in flavonoid pathway. When only TR4 was inoculation, the expression of related genes in ‘Brazilian’ mainly showed significant down-regulation, while it was mainly up-regulated in ‘Nongke No.1’. When treated with SA only, C4H and 4CL were up-regulated in the two cultivars. After SA treatment and TR4 inoculation, the expression of C4H and 4CL in the two cultivars’ maintained up-regulated trend. The up-regulation range in ‘Nongke No.1” was higher compared with ‘Brazilian’. The expression of CAD in ‘Bralizian’ was up-regulated treated with SA, while it decreased when further inoculated with TR4. The expression of CAD in ‘Nongke No.1’ was also up-regulated treated with SA, and so was it in ‘Nongke No.1’ under the double treatments with SA and TR4. CCoAOMT in ‘Brazilian’ was induced by TR4 and showed significant up-regulation. After SA treatment and TR4 inoculation, the expression of CCoAOMT in ‘Brazilian’ still maintained strong up-regulation. The expression of CCoAOMT was strongly induced up-regulation in ‘Nongke No.1’ treated only with SA or further inoculated with TR4. CHS and CHI showed significant up-regulation in the two cultivars treated with SA. And it still was up-regulated after SA and TR4 double treatments. Results indicated that exogenous SA could induce the up-regulated expression of key enzyme genes of phenylpropanoid pathway in the roots of susceptible and resistant banana cultivars and phenylpropanoid pathway plays a very important role in the induced resistance against TR4 in banana.