Expression of a ripening-related cytochrome P450 cDNA in Cavendish banana (Musa acuminata cv. Williams)

Abstract

As part of a study to understand the molecular basis of fruit ripening, this study reports the isolation and characterization of a banana cytochrome P450 (P450) cDNA, designated as MAP450-1, which was associated with fruit ripening of banana. MAP450-1 encoded a single polypeptide of 507 amino acid residues that shared an overall identity of 27-45% with that of several plant P450s, among which MAP450-1 was most related phylogenetically to the avocado P450 CYP71A1. The polypeptide that possessed residue domains conserved in all P450s was classified as CYP71N1. Expression of CYP71N1 varied greatly between banana organs. Transcripts were detected only in peel and pulp of the ripening fruit and not in unripe fruit tissues at all developmental stages or other organs (root, leaf, ovary and flower). During ripening, transcripts were barely detectable in pre-climacteric and climacteric fruits but, as ripening progressed, they began to accumulate and reached a maximum in post-climacteric fruits. CYP71N1 expression in pre-climacteric fruit could be upregulated by exogenous application of ethylene (1-5 ppm) and treatment of overripe fruit with exogenous sucrose (50-300 mM) but not glucose downregulated the expression. These results indicate that P450s may not play a role in fruit development and its expression is associated with ripening, which may be regulated, in part, by ethylene and/or sucrose, at the transcript level.