Catecholamine biosynthesis pathway potentially involved in banana defense mechanisms to crown rot disease

Variations in Cavendish bananas susceptibility to crown rot disease have been observed (Lassois et al., 2010a), but the molecular mechanisms underlying these quantitative host-pathogen relationships were still unknown. The present study was designed to compare gene expression between bananas (Musa acuminata, AAA, 'Grande-Naine') showing a high post-harvest susceptibility (S+) and bananas showing a low post-harvest susceptibility (S-) to crown rot disease. This comparison was performed between crowns (S+ and S-) collected one hour before standardized artificial inoculations with Colletotrichum musae. Fruit susceptibility was evaluated through lesion size on the crown 13 days later. Gene expression comparisons were performed with the cDNA-AFLP technique (Lassois et al., 2009). This revealed that a gene showing a strong homology with a dopamine-beta-monooxygenase (DoH) is differently expressed between S+ and S (Lassois et al., 2011). Furthermore, semi-quantitative real-time RT-PCR analyses between S+ and S- were applied to confirm the differential expression results for DoH obtained by cDNA-AFLP. Two biological replicates were tested. These semi-quantitative analyses were performed not only on tissues collected one hour before C. musae inoculation but also on crown tissues collected 13 days after inoculation. The real-time RT-PCR confirmed that DoH was upregulated in the S tissues collected at harvest, just before C. musae inoculation. This gene was also highly upregulated in the S- tissues collected 13 days after crown inoculation. Similar results were obtained for both biological replicates. Our results suggest that catecholamine's could play a role in banana defense mechanisms to crown rot disease.