Abstract
Short-chain esters derived from fatty acid contribute to the characteristic flavor of apricot fruit, and the biosynthesis of these compounds in fruit is catalyzed by alcohol acyltransferase (AAT). In this work, we investigated the AAT gene family via genome-wide scanning, and three AAT loci were identified in different linkage groups (LGs), with PaAAT1 (PARG22907m01) in LG7, PaAAT2 (PARG15279m01) in LG4, and PaAAT3 (PARG22697m01) in LG6. Phylogenetic analysis showed that PaAAT1 belongs to clade 3, while PaAAT2 and PaAAT3 belong to clade 1 and clade 2, respectively. In contrast, the three AAT genes present different expression patterns. Only PaAAT1 exhibited distinct patterns of fruit-specific expression, and the expression of PaAAT1 sharply increased during fruit ripening, which is consistent with the abundance of C4–C6 esters such as (E)-2-hexenyl acetate and (Z)-3-hexenyl acetate. The transient overexpression of PaAAT1 in Katy (KT) apricot fruit resulted in a remarkable decrease in hexenol, (E)-2-hexenol, and (Z)-3-hexenol levels while significantly increasing the corresponding acetate production (p < 0.01). A substrate assay revealed that the PaAAT1 protein enzyme can produce hexenyl acetate, (E)-2-hexenyl acetate, and (Z)-3-hexenyl acetate when C6 alcohols are used as substrates for the reaction. Taken together, these results indicate that PaAAT1 plays a crucial role in the production of C6 esters in apricot fruit during ripening.
Highlights
Apricot (Prunus armeniaca L.) is a widely cultivated temperate fruit tree species with fruit containing many phytochemicals that are nutritionally valuable components of the human diet (Aubert and Chanforan, 2007)
The present study found that PaAAT1s are globular proteins with a size of 49.905 kDa, which is in good agreement with the molecular weight of the native alcohol acyltransferase (AAT) proteins purified in banana (40 kDa), strawberry (48 kDa), grape (50 kDa), and melon (50 kDa) (Hui et al, 2010)
The gene structure and gene expression analysis indicated that PpAAT1 is putatively associated with ester formation in apricots
Summary
Apricot (Prunus armeniaca L.) is a widely cultivated temperate fruit tree species with fruit containing many phytochemicals that are nutritionally valuable components of the human diet (Aubert and Chanforan, 2007). More than 300 volatiles have been identified from apricot fruit, including aldehydes, alcohols, ketones, lactones, terpenes, and esters (Cumplido-Laso et al, 2012). C6 aldehydes and alcohols offer a green-note aroma, PaAAT1 is Involved in Esters Biosynthesis while esters and lactones are responsible for fruity aromas. Esters such as (E)-2-hexenyl acetate and (Z)-3-hexenyl acetate are considered to be key odorants influencing the flavor quality of apricot fruit (D’Auria, 2006; Fu et al, 2017). Aldehydes tend to decline in the fruit while esters increase under post-harvest treatments (Cumplido-Laso et al, 2012; Galaz et al, 2013)
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