Rate of banana fruit ripening depends on genome composition and gene expression of ethylene signaling and ethylene biosynthesis

Expression of the genes in banana peel involved in ethylene signaling and ethylene biosynthesis was investigated in three groups of cultivars showing different fruit-ripening times: a fast-ripening group (Thong Som and Namwa Pakchong 50), an intermediate-ripening group (Khai Kasetsart 2, Sa and Hom Thong), and a slow-ripening cultivar (Dwarf Cavendish). A decrease in pulp firmness was correlated with peel yellowing in these three ripening groups. Also the respiration climacteric peak correlated with the speed of ripening. The fast-ripening group had a B-genome composition and a high level of ACO gene expression. The transcripts of MaERS1, MaERS3, MaEIL1-4, and MaACS1, MaACO1 genes had differential expression levels. A reduced expression level of the ethylene receptor gene (MaERS3) was observed in the fast-ripening group, while the expression of the MaERS1 gene increased markedly at the mature green stage until the peel turned yellow. However, there was less change in both receptor genes in the intermediate-ripening group. In the slow-ripening group, the expression levels of these receptor genes continuously increased throughout the ripening time concomitant with the expression of the MaCTR1 gene. These results indicated that ethylene biosynthesis (MaACS1 and MaACO1) was being delayed. In conclusion, the distinct regulation of banana fruit-ripening time, resulting from the reduced expression level of ethylene receptor genes, depended on the combination of the B and A genomes contributing to each subspecies.