MaMADS1 and MaMADS2 Are Components of the Signaling Pathway of Fruit Ripening in Banana

Transcription factors of the MADS-box gene family were established in tomato as components of the ripening pathway acting upstream of ethylene production. In this study we have found out that at least two banana’s MADS box genes, MaMADS1 and MaMADS2 are controlling climacteric respiration and ethylene production. Six MaMADS box genes were cloned from banana fruit and their temporal expression during ripening and spatial expression at various organs have been determined. By using specific antibodies created against MaMADS2, we have performed chromatin immuneprecipitation (ChI) to identify potential target genes. In addition, we have created three types of transgenic banana plants exhibiting reduced levels of either MaMADS1 or MaMADS2 expression.

Our results show that both MaMADS1 and MaMADS2 are expressed at higher levels in fruit than other organs, suggesting a specific involvement in fruit ripening. the MaMADS-box genes expression in banana is dynamically changing after harvest and most of them are induced at the onset of the climacteric peak. Different MaMADS box genes are expressed in pulp and peel and they are differently affected by ethylene, indicating that the signaling pathway is different between these tissues.  Only the MaMADS2 box gene expression is not affected by ethylene, indicating that this gene might act upstream to the ethylene response pathway. In transgenic banana plants with reduced levels of either MaMADS1 or MaMADS2, climacteric respiration and ethylene production and hence ripening were reduced. This clearly suggests that both genes are responsible for banana fruit ripening. At least for MaMADS2, we found by ChI that ACC oxidase  and ACC synthase, key enzymes of the ethylene biosynthesis pathway, are targets of MaMADS2, further substantiating the role of MaMADS2 as a component of the ripening pathway. Since fruit quality was not altered in the transgenic fruit, this approach can serve in the future to extend banana shelflife.