A comparative study of cultivar differences in sucrose phosphate synthase gene expression and sucrose formation during banana fruit ripening

Abstract

Sucrose phosphate synthase (SPS) (E.C.2.4.1.14) is the key enzyme for sucrose formation in banana. A comparative analysis of expression profiles of SPS was carried out in association with sucrose metabolism patterns during fruit ripening in three banana cultivars, Cavendish (AAA), Kanthali (AB) and Monthan (AAB). Analysis of the transcript and protein accumulation patterns of the SPS gene during ripening revealed differential timing in expression of the gene which correlated well with variation in sucrose metabolism patterns in the three cultivars. The expression levels of SPS increased considerably during early ripening in Cavendish after exogenous application of ethylene, while in Kanthali ethylene treatment only moderately increased SPS expression during postharvest ripening. In Monthan, expression of SPS was very low throughout ripening and ethylene treatment did not stimulate the expression of the gene in this cultivar. Analysis of a promoter fragment of SPS in the three cultivars revealed a putative reverse GCC-box ERE motif. DNA-protein interaction studies demonstrated the role of this regulatory element in differential transcriptional regulation of SPS. Overall our results provide information about sucrose metabolism patterns at the physiological and molecular levels during fruit ripening in three natural banana cultivars.