Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/25/2008
Publication Date: 6/14/2008
Citation: Zhu, Y., Rudell Jr, D.R., Mattheis, J.P. 2008. Characterization of cultivar differences in alcohol acyltransferase and 1-aminocyclopropane-1carboxylate synthase gene expression and volatile compound emission during apple fruit maturation and ripening. Postharvest Biology and Technology 49:(3):330-339. Interpretive Summary: Apple fruit aroma is an important indicator for consumer quality. Vast of apple aroma is composed of esters. Apple cultivars 'Golden Delicious' and 'Granny Smith' represent two phenotypic extremes in volatile compound production. The objective of this study was to compare the expression patterns of four AAT genes; for volatile ester biosynthesis, and two ACS genes, for ethylene biosynthesis, and to examine their potential relationship with volatile production exists during on-tree development and postharvest ripening. The levels of AAT1 and AAT2 expression were consistent with the total amount of esters detected between both cultivars. The results suggest that differential expression of AAT may contribute to regulation of apple fruit volatile ester biosynthesis, and that expression patterns of ACS3 but not ACS1 are consistent with those of AAT1 and AAT2. These results could lead to the generation of molecular marker for apple breeding and novel postharvest biotechnology.
Technical Abstract: Alcohol acyl transferase (AAT) catalyzes the last step of volatile ester biosynthesis, and ethylene purportedly regulates AAT gene expression. In this study, expession patterns of four apple AAT genes and two ethylene biosynthesis genes were investigated in two apple cultivars with relatively high ('Golden Delicious') or low ('Granny Smith') volatile ester production. All four AAT genes were more strongly and consistently expressed in 'Golden Delicious' than in 'Granny Smith'. Of the four AAT genes evaluated, AAT1 and AAt2 were highly expressed compared to AAT3 and AAT4. The levels of AAT1 and AAT2 expression were consistent with the total amount of esters detected between both cultivars. The transcript levels of AAT3 and AAT4 decreased at or after the onset of ripening in both cultivars, and expression was low or not detectable during postharvest ripening after harvest. Two 1-aminocycloprpane-1-carboxylate synthase (ACS) genes are known expressed in apple fruit tissues. The expression of ACS1 was induced after the onset of ripening while the expression of ACS3 was detected throughout the harvest period in both cultivars. ACS1 expression ws detected throughout the six week ripening period for both cultivars as was ACS3 expression in 'Golden Delicious'. Postharvest 1-MCP exposure had little impact on expression of AAT and ACS3 genes, but substantially suppressed the transcript level for ACS1 in both cultivars. The results suggest that differential expression of AAT may contribute to regulation of apple fruit volatile ester biosynthesis, and that expression patterns of ACS3 but not ACS1 are consistent with those of AAT1 and AAT2.