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.

Longan is an exotic tropical fruit crop and exhibits off‐season flowering induced by potassium chlorate (KClO ₃ ), though the molecular mechanisms remain unclear. We assembled a high‐quality, 441.5 Mb genome of variety ‘Shixia’, with a contig N50 at 28.1 Mb, 29, 325 protein‐coding genes, 26 telomeres and 15 centromeres. Comparative genomic analysis with lychee revealed structural variations potentially driving gene family expansions related to flavone biosynthesis and disease resistance. Transcriptomic profiling showed that natural flowering appears to be primarily regulated by photoperiod, vernalisation and autonomous pathways, while KClO ₃ ‐induced flowering may preferentially activate the gibberellin pathway at 5 days after treatment (DAT) and autonomous pathways at 10 DAT, involving putative repression of DlDDF1 , DlFLCs and DlSVPs , and up‐regulation of DlWRKY75_2 . In the perpetual‐flowering variety ‘Sijimi’, elevated expression of photoperiod genes, such as DlCOR28 , DlCOR27 , DlADO3 , DlPRR5 , DlGI and DlJMJ30 , may explain its perpetual blooming. Overexpression of DlDDF1 in Arabidopsis delayed flowering, partially reversed by KClO ₃ through an increase in bioactive GA ₄ . Together, KClO ₃ ‐induced flowering likely involves oxidative stress response and gibberellin signalling via DlDDF1 repression, while natural flowering relies on seasonal cues. These results lay the foundation for longan genetic improvement.

Nowadays, there are few reports about regulatory genes implicated in peel color of longan. The basic genetic research of longan has been in stagnation for a long time as a lack of transcriptomic and genetic information. To predict candidate genes associated with peel color, Gene Functional Annotation and Coding Sequence prediction were used to perform functional annotation for our assembled unigenes and investigate differentially expressed genes (DEGs) of fruitlet peels from Longli (Dimocarpus confinis). Finally, a total of 24,044 (44.19 %) unigenes were annotated at least in one database after BLAST search to NCBI non-redundant protein sequence, NCBI non-redundant nucleotide sequences, Kyoto Encyclopedia of Genes and Genomes (KEGG) Ortholog, manually annotated and reviewed protein sequence database (Swiss-Prot), Protein family, Gene Ontology, euKaryotic Ortholog Groups databases. After searching against the KEGG-GENE protein database, a result of 6228 (11.45 %) unigenes were assigned to 245 KEGG pathways. Via comparing the distributions of expression value of all corresponding unigenes from red peel and green peel fruit, it could be intuitively concluded that high similarity was existed in the two distributions; however, on the whole, between two distributions of log RPKM expression value, some differences indicated that expression level in green-peel fruit group is slightly higher than values in red-peel fruit group. Finally, a total of 1349 unigenes were identified as DEGs after blasting the DEGs to public sequence databases, and 32 peel-color-related genes were identified in longan. Our results suggest that a number of unigenes involved in longan metabolic process, including anthocyanin biosynthesis. In addition, DRF, F3H, ANS, CYP75A1 and C1 may be the key ones. The study on key genes related to peel color will be contributed to revealing the molecular mechanisms of regulating peel color in woody plants.

Loquat is an evergreen fruit crop which blooms from autumn–winter, and supports human beings with juicy fruit from late spring to early summer. However, the most traditional cultivars of this crop produce small fruit and bear a much lower yield than its relatives like apple, pear and peach. Large-size cultivars have long been a cherished aim of breeders for improving the production yield of loquat. Agronomic practices like panicle thinning, fruit thinning, growth regulator application, fertilization and so on are easier and more accessible ways for growers to produce large-size loquat fruit on existing production trees. Here, we develop a novel pruning method with an annual double back-cut, which provides vigorous shoot with more leaves and thicker branches for bearing much larger loquat fruit. Cellular observation determined that the vigorous shoot training method motivated cell division to produce larger loquat fruit, and that most of these cell layers were proliferated before the appearance of flower blossoms. Gene expression data of four development stages showed that EjFWL1 and EjFWL2 were notably downregulated in flower buds of the vigorously pruned tree. The data here further confirmed that the cell division capacity during flower development greatly influenced both the flower and fruit size of loquat. More importantly, we developed a novel pruning method to inhibit cell division repressors, promote cell proliferation and enlarge fruit size in loquat.

γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid, with many regulatory effects in humans. It aids in regulating blood glucose levels and pressure and is widely recognized for its ability to promote cognitive balance through the alleviation of stress and improvements in sleep quality. The GABA content of longan pulp is higher than that of many other fruits and vegetables; however, much is still unknown about GABA’s biosynthesis in longan. In this study, we found that the GABA content of ‘Baoshi No. 1’ (BS1) pulp was significantly higher than that of ‘Chunxiang’ (CX) pulp. The GAD activity was higher in BS1 pulp than CX pulp, while there was no significant difference in the GABA-T activity. Additionally, five GAD genes were identified in longan, and an analysis of their transcriptional levels showed that only the expression level of DlGAD3 corresponded to the GABA content and GAD activity. DlGAD3 was localized in the cytoplasm, and its transient overexpression promoted an increase in the GABA content in Nicotiana benthamiana leaves. Overall, our results show that DlGAD3 is able to promote the accumulation of GABA and may play a major role in its biosynthesis in longan pulp.