S01 - Session O7 - Alternative splicing of acetohydroxyacid synthase and isopropylmalate synthase provides means for production of ‘Cavendish’ banana fruit aroma

Authors: Philip Engelgau *, Randolph Beaudry

Despite the importance and popularity of 'Cavendish' banana fruit, little is known concerning the regulation of the biosynthesis of the odor-active volatiles which provide its unique aroma. Branched-chain (BC) esters composed of 2-methylpropyl and 3-methylbutyl elements are responsible for imbuing the distinctive aroma of 'Cavendish' banana fruit and are derived from the same metabolic paths as valine and leucine, respectively. While these BC amino acids accumulate in fruit pulp during ripening, it is unclear how they are able to. The production of valine and leucine is under strict feedback mechanisms that should prevent such stark increases. Here we present the finding that alternative splicing of two otherwise feedback-inhibited enzymes, acetohydroxyacid synthase (AHAS) and isopropylmalate synthase (IPMS), produces isoforms with compromised regulatory domains. Expression of these key enzymes was found to increase several-fold at the peak of ethylene production with the ratio of the alternative splice forms representing up to 6 or 20% for AHAS and IPMS, respectively, of the total expression at peak aroma production. Furthermore, these alternative splice forms were only found in pulp tissues, with a minor percentage detected in peel tissues. Expression of the alternative splice forms were not found in root, pseudostem, leaf, peduncle, bract, anther or ovary tissue. Further respiratory, aroma and intermediary metabolite data illustrate a coordinated induction of this unregulated pathway, which allows the production of this characteristic aroma of 'Cavendish' banana fruit.