Abscisic acid is involved in aromatic ester biosynthesis related with ethylene in green apples

The production of aromatic volatiles such as esters during the ripening process in climacteric fruits is known to be controlled by ethylene. However, we here show that abscisic acid (ABA) application accelerated the onset of short-chain ester production (hexyl propionate, ethyl-2-methyl butyrate) and the expression of biosynthesis genes (MdAAT2 and MdBCAT1) during ripening of 'Orin' apple. ABA application also promoted the production of ethylene, and caused ethylene peak shifts correlated with the expression of ethylene synthesis genes (MdACS1/3 and MdACO1), suggesting that ABA may act jointly with ethylene as a positive regulator at the ripening stage of 'Orin' apple. Additionally, endogenous levels and expression of biosynthesis (MdNCED1) and signal transduction genes (MdABF2-like) of ABA increased towards ripening. Finally, the localization of the putative MdABF2-like protein binding element, AREB/ABF, was observed in the 5'-upstream region of MdACS1/3 and MdACO1.