Transcriptome analysis of ripe and unripe fruit tissue of banana identifies major metabolic networks involved in fruit ripening process

BACKGROUND: Banana is one of the most important crop plants grown in the tropics and sub-tropics. It is a climacteric fruit and undergoes ethylene dependent ripening. Once ripening is initiated, it proceeds at a fast rate making postharvest life short, which can result in heavy economic losses. During the fruit ripening process a number of physiological and biochemical changes take place and thousands of genes from various metabolic pathways are recruited to produce a ripe and edible fruit. To better understand the underlying mechanism of ripening, we undertook a study to evaluate global changes in the transcriptome of the fruit during the ripening process. RESULTS: We sequenced the transcriptomes of the unripe and ripe stages of banana (Musa accuminata; Dwarf Cavendish) fruit. The transcriptomes were sequenced using a 454 GSFLX-Titanium platform that resulted in more than 7,00,000 high quality (HQ) reads. The assembly of the reads resulted in 19,410 contigs and 92,823 singletons. A large number of the differentially expressed genes identified were linked to ripening dependent processes including ethylene biosynthesis, perception and signalling, cell wall degradation and production of aromatic volatiles. In the banana fruit transcriptomes, we found transcripts included in 120 pathways described in the KEGG database for rice. The members of the expansin and xyloglucan transglycosylase/hydrolase (XTH) gene families were highly up-regulated during ripening, which suggests that they might play important roles in the softening of the fruit. Several genes involved in the synthesis of aromatic volatiles and members of transcription factor families previously reported to be involved in ripening were also identified. CONCLUSIONS: A large number of differentially regulated genes were identified during banana fruit ripening. Many of these are associated with cell wall degradation and synthesis of aromatic volatiles. A large number of differentially expressed genes did not align with any of the databases and might be novel genes in banana. These genes can be good candidates for future studies to establish their role in banana fruit ripening. The datasets developed in this study will help in developing strategies to manipulate banana fruit ripening and reduce post harvest losses.