Induced Resistance to Fusarium wilt

In the last century, Fusarium wilt of banana (FWB) destroyed the banana cultivar Gros Michel. The Cavendish cultivars saved the global banana industry, and currently they dominate global production (~50%) and the export trade (~95%). However, a new strain called Tropical Race 4 (TR4) surfaced in the late 1960's, spread globally and greatly damages Cavendish plantations as well as manifold local varieties that are primarily grown by small holders. Presently, there is no commercially available replacement for Cavendish and hence control strategies have to be developed and implemented to manage FWB. Here, we studied whether it is possible to induce resistance to TR4 by pre-inoculations with different Fusarium spp. Only pre-treatments with an avirulent Race 1 strain significantly reduced disease development of TR4 in a Cavendish genotype and this effect was stable at various nutritional and pH conditions. We then used transcriptome analysis to study the molecular basis of this response. Several genes involved in plant defence responses were up-regulated during the initial stages of individual infections with TR4 and Race 1, as well as in combined treatments. In addition, a number of genes in the ethylene and jasmonate response pathways as well as several gibberellin synthesis associated genes were induced. We observed upregulation of RGA2 like genes in all treatments. Hence, RGA2 could be a key factor involved in both R1 and TR4 resistance. The data support the hypothesis that activating resistance to Race 1 in Cavendish bananas affects TR4 development and provide a first insight of gene expression during the interaction between various Fusarium spp. and banana.20世纪以来，香蕉枯萎病（Fusarium Wilt of Banana, FWB）曾摧毁大麦克（Gros Michel）香蕉品种。华蕉（Cavendish）品种挽救了全球香蕉产业，目前其占据全球香蕉产量约50%、出口贸易约95%的份额。然而，一种名为热带4号小种（Tropical Race 4, TR4）的新型菌株于20世纪60年代末出现并全球扩散，不仅严重破坏华蕉种植园，还对大量以小农户种植为主的地方品种造成极大损害。目前尚无商业化可替代华蕉的香蕉品种，因此必须开发并实施防控策略以应对香蕉枯萎病。本研究旨在探究通过接种不同尖孢镰刀菌属（Fusarium spp.）菌株进行预接种，是否能够诱导植株对TR4产生抗性。仅使用无致病力的1号小种（Race 1）菌株进行预处理，可显著抑制华蕉基因型植株感染TR4后的病情发展，且该效应在不同营养条件与pH环境下均保持稳定。随后本研究通过转录组分析（transcriptome analysis），探究该抗性响应的分子机制：在单独接种TR4、1号小种以及复合接种的初始阶段，多个参与植物防御反应的基因均呈现上调表达；此外，乙烯（ethylene）与茉莉酸（jasmonate）信号通路中的诸多基因，以及多个与赤霉素（gibberellin）合成相关的基因均被诱导表达。本研究在所有处理组中均观察到RGA2类基因（RGA2 like genes）的上调表达，因此RGA2可能是同时参与1号小种与TR4抗性调控的关键因子。本研究数据支持“激活华蕉对1号小种的抗性可影响TR4的侵染发展”这一假说，并首次揭示了不同尖孢镰刀菌属菌株与香蕉互作过程中的基因表达特征。