Identification of defense-related genes in banana roots infected by Fusarium oxysporum f. sp. cubense tropical race 4

Abstract

Fusarium oxysporum f. sp. cubense tropical race 4 is a lethal pathogen, affecting banana production by causing vascular wilt. To date, the molecular basis of resistant cultivars is largely unknown. In this study, suppression subtractive hybridization (SSH) libraries were constructed for the roots of two iso-line cultivars—a Foc-susceptible cultivar and its tolerant mutant—using both uninfected controls and plants artificially challenged with pathogen conidiospores. Unigenes from SSH libraries were used to develop a cDNA array, and then microarray analysis was carried out to verify those genes exhibiting differential expression. A total of 257 unigenes was obtained from the SSH libraries and microarray detection confirmed that most of them were differentially expressed. Of these, 116 unigenes had matched proteins in gene ontology and were classified into 38 different functional groups. The transcript levels of up to 19 putative defense genes were followed for a whole infection period in four cultivars differing in resistance level. At the early stages of infection (within 48 h), nineteen genes varied by a factor of more than three, subsequently only four genes (Pectinesterase inhibitor, PEI; Peroxidase, POD; Pathogenesis-related protein 1, PR1; and Pathogenesis-related protein 3, PR3) maintained their up-regulation. This indicates that anti-oxidation, cell wall modification and synthesis of anti-fungal proteins are the most important aspects to study if we are to understand the Foc resistance mechanism in commercial banana plants.