Banana sucrose-phosphate synthase gene expression during fruit ripening

A 952-base pair polymerase-chain-reaction product of sucrose-phosphate synthase (SPS) (EC 3.3.1.14) from banana (Musa acuminata cv. Nanicao) fruit was cloned and used to study expression of the enzyme during development and ripening. The deduced amino acid sequence shows that banana SPS has a high homology with the leaf, tap-root and bean enzymes from other species. Enzyme activity, and mRNA and protein levels point to an increase in SPS expression during ripening. The accumulation of sucrose was correlated to starch degradation and happened 4 d after SPS mRNA and activity had reached their maxima. These results indicate that access to substrate and transcriptional activation with increase in SPS expression might be important regulatory events of sweetening during banana fruit ripening.