Abstract
Simple SummaryIn this study, three longan cultivars, including non-aroma types ‘Shixia’ (SX), ‘Lidongben’ (LDB), and strong aroma type ‘Xiangcui’ (XC), were selected to analyze free amino acids (FAAs) variations at six distinct growth stages. The genome-wide identification and expression analysis of genes related to the branched-chain amino acids (BCAA) synthesis pathway were carried out. Results showed that thirty-six FAAs were identified, which increased drastically with fruit development until ripening. During the period of rapid fruit expansion, the aroma of XC changed from light to strong, and the contents of L-alanine and L-leucine were significantly higher than those of SX and LDB. The content of Leu was negatively correlated with the expression of DilBCAT1, -6, and -9 in three varieties, but positively correlated with DilBCAT16, indicating that these four genes may be responsible for the different synthesis and degradation of Leu among cultivars.Amino acids are important component of fruit nutrition and quality. In this study, three longan cultivars, including non-aroma types ‘Shixia’ (SX), ‘Lidongben’ (LDB), and strong aroma type ‘Xiangcui’ (XC), were selected to analyze free amino acids (FAAs) variations at six distinct growth stages (S1–S6). The genome-wide identification and expression analysis of genes related to the branched-chain amino acids (BCAA) synthesis pathway were carried out. Results showed that 36 FAAs were identified, and the total FAAs content ranged from 2601.0 to 9073.5 mg/kg, which increased drastically with fruit development until ripening. L-glutamic acid (Glu), L-alanine (Ala), L-arginine (Arg), γ-Aminobutyric acid (GABA), L-aspartic acid (Asp), L-leucine (Leu), hydroxyl-proline (Hypro), and L-serine (Ser) were the predominant FAAs (1619.9–7213.9 mg/kg) in pulp, accounting for 62.28–92.05% of the total amino acids. During the period of rapid fruit expansion (S2–S4), the aroma of XC changed from light to strong, and the contents of L-alanine (Ala) and L-leucine (Leu) were significantly higher than those of SX and LDB. Furthermore, a total of two 2-isopropyl malate synthase (IPMS), two 3-isopropyl malate dehydrogenase (IPMD), and 16 BCAA transferase (BCAT) genes were identified. The expression levels of DilBCAT1, -6, and -9 genes in XC were significantly higher than those in SX and LDB, while DilBCAT16 in XC was lower. The content of Leu was negatively correlated with the expression of DilBCAT1, -6, and -9 in three varieties, but positively correlated with DilBCAT16, indicating that these four genes may be responsible for the different synthesis and degradation of Leu among cultivars.
Highlights
Longan (Dimocarpus longan Lour.) is an economically important crop in tropical and subtropical regions of Southeast Asia i.e., China, Thailand, Vietnam, etc
The entire fruit developmental process was divided into 6 stages i.e., S1–S6
A heatmap cluster analysis was conducted to illustrate the content difference of these discriminant metabolites among three cultivars (Figure 2D), and the results showed that the aromatic genotype (XC) had a greater tendency to accumulate glutamic acid (Glu), Leu, Ser, and Ala than non-aromatic genotypes (SX and LDB) during fruit development
Summary
Longan (Dimocarpus longan Lour.) is an economically important crop in tropical and subtropical regions of Southeast Asia i.e., China, Thailand, Vietnam, etc. Longan possesses numerous nutritional and functional components, including polysaccharides [1], amino acids [2,3], polyphenols and alkaloids [4,5], flavonoids, lipids [6], organic acids, vitamin C, minerals [7,8], and volatile compounds [9]. Amino acids exist in both bound and free forms in plants. The bound amino acids of longan are not hydrolyzed immediately during the course of eating and have little contribution to the flavor. Each FAA has its own taste–as one of or a combination of sweet, bitter, umami, salty, and sour [10] which directly or indirectly affects the taste and even aroma of longan fruit. The component identification and dynamic change analysis of FAAs in different longan varieties during ripening can help understand the essence of the formation of flavor quality
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