Inoculation with arbuscular mycorrhizal fungus modulates defense-related genes expression in banana seedlings susceptible to wilt disease

Banana as an important economic crop worldwide, often suffers from serious damage caused by Fusarium oxysporum f. sp. Cubense. Arbuscular mycorrhizal (AM) fungi have been considered as one of the promising plant biocontrol agents in preventing from root pathogens. This study examined the effect of AM fungal inoculation on plant growth and differential expressions of growth- and defense-related genes in banana seedlings. Tissue-cultured seedlings of Brazilian banana (Musa acuminate Cavendish cv. Brail) were inoculated with AM fungus (Rhizophagus irregularis, Ri), and developed good mycorrhizal symbiosis from 4 to 11 weeks after inoculation with an infection rate up to 71.7% of the roots system. Microbial abundance revealed that Ri abundance in banana roots was 1.85×106 copies/ml at 11 weeks after inoculaiton. Inoculation improved plant dry weights by 47.5, 124, and 129% for stem, leaf, and the whole plant, respectively, during phosphate depletion. Among a total of 1411 differentially expressed genes (DEGs) obtained from the transcriptome data analysis, genes related to plant resistance (e.g. POD, PAL, PYR, and HBP-1b) and those related to plant growth (e.g. IAA, GH3, SAUR, and ARR8) were up-regulated in AM plants. This study demonstrates that AM fungus effectively promoted the growth of banana plants and induced defense-related genes which could help suppress wilt disease. The outcomes of this study form a basis for further study on the mechanism of banana disease resistance induced by AM fungi.香蕉作为全球重要的经济作物，常遭受古巴尖孢镰刀菌（Fusarium oxysporum f. sp. Cubense）引发的严重为害。丛枝菌根（Arbuscular mycorrhizal, AM）真菌被认为是防治植物根部病原菌的极具潜力的生防因子之一。本研究探究了AM真菌接种对香蕉幼苗生长以及生长、防御相关基因差异表达的影响。本研究以巴西香蕉（Musa acuminate Cavendish cv. Brail）组培幼苗为材料，接种AM真菌异形根孢囊霉（Rhizophagus irregularis, Ri），接种后4至11周，二者建立了良好的菌根共生关系，根系侵染率最高可达71.7%。微生物定量结果显示，接种后11周，香蕉根系内Ri的丰度可达1.85×10^6 拷贝/毫升。在磷胁迫条件下，接种处理使植株茎、叶及全株干重分别提升47.5%、124%及129%。转录组数据分析共获得1411个差异表达基因（differentially expressed genes, DEGs），其中AM真菌接种植株的植物抗性相关基因（如过氧化物酶POD、苯丙氨酸解氨酶PAL、吡咯啉-5-羧酸合成酶PYR、转录因子HBP-1b等）及植物生长相关基因（如吲哚乙酸IAA、GH3家族基因、小生长素上调RNA SAUR、响应调节因子ARR8等）均呈上调表达。本研究表明，AM真菌可有效促进香蕉植株生长，并诱导防御相关基因表达，从而有助于抑制香蕉枯萎病。本研究结果为后续解析AM真菌诱导香蕉抗病性的分子机制奠定了基础。