Differential gene expression in banana roots in response to Fusarium wilt

Banana wilt disease, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a devastating disease in the banana industry. The molecular mechanism underlying the wilt resistance of AAA-type banana cultivars has not been fully characterized. Our objective was to analyse the genes differentially expressed in roots during the time of flower bud differentiation in plants grown in fields infested with Foc TR4. We compared the Foc TR4-tolerant ‘Formosana’ banana and the susceptible ‘Brazil’ banana. cDNA libraries were constructed from RNA isolated from the roots of both cultivars, and generated approximately 40 million and 35 million high-quality reads, respectively. We mapped 28 353 810 ‘Formosana’ reads and 26 917 421 ‘Brazil’ reads to the banana genome. A search of the NR (non-redundant) database resulted in the annotation of 34 408 genes. Additionally, 107 genes were differentially expressed between the two cultivars. Among the 48 differentially expressed genes with known functions, 41 were expressed more highly in ‘Formosana’ than in ‘Brazil’. These genes were divided into several categories, including specific resistance mechanism-related enzyme genes and phytoalexin synthesis-related genes. The expression levels of eight genes were validated by a quantitative real-time polymerase chain reaction. Our results indicate that ‘Formosana’ may enhance its tolerance to Foc TR4 by increasing the expression of defence-related genes (possibly constitutively). This cultivar also exhibits up-regulated expression of non-specific stress-related genes, which may enhance its overall disease tolerance. This study provides important transcript-level details potentially useful for clarifying the molecular mechanism underlying the disease resistance of Cavendish banana cultivars.