Molecular characterisation of a fruit ripening-related INDETERMINATE DOMAIN transcription factor in banana (Musa acuminata)

Abstract

SummarySome INDETERMINATE DOMAIN (IDD) genes are reported to function in sugar metabolism and as floweringtime regulators. However, it is unknown whether IDD genes are also associated with fruit ripening. In this work, a novel cDNA from an IDD gene, designated MaIDD, was isolated and characterised from banana (Musa acuminata) fruit using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods. MaIDD contained an open reading frame of 1,680 bp encoding a putative polypeptide of 559 amino acid residues, with a molecular mass of 59.6 kDa. The predicted protein (GenBank Accession No. AAC18941) showed 50.87% sequence similarity to AtIDD5 (AEC05542) from Arabidopsis. The deduced protein sequence featured a conserved TRDFLG motif, a nuclear localisation signal, and four distinct zinc finger motifs (ZFs), thereby showing the typical characteristics of products of the IDD gene family. In addition, the MaIDD protein possessed transcriptional activity in yeast and was localised in the nucleus by applying sub-cellular localisation analysis. Moreover, quantitative real-time PCR (qPCR) analysis showed that the MaIDD gene was differentially expressed in various banana organs and showed relatively higher transcript levels in the peel and pulp of fruit at an early stage of development (3 weeks after anthesis), indicating that expression of MaIDD may be associated with the early development of banana fruit. Transcript levels of MaIDD in the peel and the pulp increased during natural or ethylene-induced fruit ripening, while transcript levels decreased in the peel and pulp in 1-methylcyclopropene-treated, ripening-inhibited fruit, suggesting that MaIDD could be associated with fruit ripening. Taken together, our results suggest that MaIDD is an activator of transcription and may be related to the early development and ripening of banana fruit.