Expression of a UDPglucose pyrophosphorylase cDNA during fruit ripening ofbanana (Musa acuminata)

We report the isolation of a banana cDNA, designated MWUGPA, encoding uridi ne diphosphoryl (UDP)-glucose pyrophosphorylase (UGPase, EC. 2.7.7.9) that catalyses the reversible conversion between glucose 1-phosphate and UDPgluc ose in plants and animals. Furthermore, UGPase expression in fruit during r ipening and in response to exogenous ethylene and sugars was also investiga ted. MWUGPA encodes a polypeptide of 467 amino acid residues and shares a h igh degree of sequence similarity (85-90%) with other plant UGPase homologs . In northern blot analysis, a 1.7-kb UGPase transcript was detected in bot h the vegetative and reproductive organs, but the former was considerably l ess abundant than the latter. In fruit, the level of accumulated transcript s was higher in pulp than peel at all ripening stages. Transcript abundance in both fruit tissues was relatively constant during ripening, but pulp tr anscripts surged in the 'more green than yellow' category fruit when ethyle ne also increased. Further analysis revealed that UGPase expression in frui t was ethylene-inducible, but the response was tissue-specific, as evidence d by the promoting effect of exogenous ethylene on accumulation of UGPase t ranscripts in pulp but not peel. Exogenous application of sucrose and fruct ose also increased UGPase transcript abundance in leaf and fruit tissues, e specially pulp, whereas exogenous glucose had little or no effect. The resu lts of this study indicate that ethylene and soluble sugars may play a regu latory role in UGPase expression during ripening in banana fruit.