R2R3-MYB is an important transcription factor family that regulates plant growth and development. Root development directly affects the absorption of water and nutrients by plants. Therefore, to understand the regulatory role of R2R3-MYB transcription factor family in root development of longan, this study identified the R2R3-MYB gene family members at the genome-wide level, and analyzed their phylogenetic characteristics, physical and chemical properties, gene structure, chromosome location and tissue expression. The analysis identified 124 R2R3-MYB family members in the longan genome. Phylogenetic analysis divided these members into 22 subfamilies, and the members of the unified subfamily had similar motifs and gene structures. The result of qRT-PCR showed that expression levels of DlMYB33, DlMYB34, DlMYB59, and DlMYB77 were significantly higher in main roots than in lateral as opposed to those of DlMYB35, DlMYB69, DlMYB70, and DlMYB83, which were significantly lower. SapBase database prediction and miRNAs sequencing results showed that 34 longan miRNAs could cleave R2R3-MYB, including 17 novel miRNAs unique to longan. The qRT-PCR and subcellular localization experiments of DlMYB92 and DlMYB98 showed that DlMYB92 is a key factor that regulates transcription in the nucleus and participates in the regulation of longan lateral root development. Longan also has a conserved miRNA-MYB-lateral root development regulation mechanism. This study provides a reference for further research on the transcriptional regulation of the miRNA-R2R3-MYB module in the root development of longan.

Longan (Dimocarpus longan L.) is one of the most important tropical and subtropical fruits in the world. Longan fruit has high nutritional and medical value, and is regarded as a treasure among fruits. Since it was first reported that potassium chlorate (KClO₃) could be successfully applied to promote flowering in longan, this compound has been widely used in the production of on-season and off-season longan fruits. KClO₃ has thus played a great role in promoting the development of the longan industry. In this review, we summarize the application methods, influencing factors, and physiological and molecular mechanisms associated with KClO₃-mediated induction of longan flowering. It can be deduced that leaves may play a crucial role in the transport of and response to KClO₃. Leaves supply carbon and nitrogen nutrition, and hormone and signaling molecules needed for the differentiation of apical buds. Moreover, cytokinins may be crucial for KClO₃-mediated induction of longan flowering. More effort should be focused on studying the molecular mechanisms underlying this process. This will not only help us to better understand floral induction by KClO₃ in longan but also enrich our understanding of flowering regulation mechanisms in woody plants.

Litchi downy blight (LDB) caused by Peronophythora litchii destroys 20–30% of litchi fruit every year and causes significant economic losses. Some Exiguobacterium strains exhibit considerable promise in both agricultural and industrial sectors. E. acetylicum SI17, isolated from the litchi fruit carposphere, demonstrated significant biocontrol activity against LDB through pre-harvest treatment. To elucidate its underlying regulatory mechanisms, the genome of SI17 was sequenced and analyzed, revealing a circular chromosome spanning 3,157,929 bp and containing 3541 protein-coding genes and 101 RNA genes. Notably, 94 genes were implicated in the production of secondary metabolites. Among the 29 Exiguobacterium strains so far sequenced, SI17 possessed the largest genome. In the phylogenomic analysis encompassing the entire genome, SI17 was clustered into Group I. Treating litchi fruit with SI17 before harvesting resulted in a decrease in H₂O₂ content in the fruit peel and an increase in superoxide dismutase activity, thus enhancing resistance to LDB. Interestingly, SI17 did not display plate antagonism against Peronophythora litchii SC18. It can be inferred that SI17 generates secondary metabolites, which enhance litchi’s resistance to LDB. This study represents the first documentation of an Exiguobacterium strain exhibiting a role in litchi plant disease and showcasing significant potential for the biological control of LDB.

Longan (Dimocarpus Longan) is one of the most important fruit crops in Southern China. Lack of available Mg in acidic soil conditions is a limitation to further increasing longan yield. Magnesium transporter (MGT/MRS2) mediates the uptake, transport, and redistribution of Mg2+ in higher plants. To understand the role of MGTs family members in longan Mg deficiency. We identified and analyzed the protein characteristics, phylogeny, expression changes, subcellular localization, and transcriptional regulation of DlMGTs members. The results showed that, twelve DlMGTs are localized in the cell membrane, chloroplast, and nucleus. The evolutionary differences in MGTs between herbaceous and woody species in different plants. The DlMGTs promoters contained many cis-acting elements and transcription factor binding sites related to the hormone, environmental, and stress response. Subcellular localization assays showed that DlMGT1 localizes in the cell membrane of Arabidopsis protoplasts. The candidate transcription factor DlGATA16, which may regulate the expression of DlMGT1, was localized in the nucleus of tobacco leaves. Dual luciferase analysis demonstrated that DlGATA16 is a potential factor regulating the transcriptional activity of DlMGT1. In this study, we identified and analyzed DlMGTs on a genome-wide scale and the subcellular localization and interaction of DlMGT1 and DlGATA16, which has important implications for further functional analysis studies of MGTs and the use of MGT for longan genetic improvement.

Potassium chlorate can promote off-season flowering in longan, but the molecular mechanisms are poorly understood. In this study, four-year-old ‘Shixia’ longan trees were injected in the trunk with potassium chlorate, and terminal buds were sampled and analyzed using transcriptomics and bioinformatics tools. To generate a reference longan transcriptome, we obtained 207,734 paired-end reads covering a total of 58,514,149 bp, which we assembled into 114,445 unigenes. Using this resource, we identified 3,265 differentially expressed genes (DEGs) that were regulated in longan terminal buds in response to potassium chlorate treatment for 2, 6 or 30 days, including 179 transcription factor genes. By reference to the Arabidopsis literature, we then defined 38 longan genes involved in flowering, from which we constructed the longan flowering pathway. According to RNA-seq data, at least 24 of these genes, which participate in multiple signaling pathways, are involved in potassium chlorate-stimulated floral induction, and the differential regulation in terminal buds of ten floral pathway genes (GI, CO, GID1, GA4, GA5, FLC, AP1, LFY, FT and SOC1) was confirmed by qRT-PCR. These data will contribute to an improved understanding of the functions of key genes involved in longan floral induction by potassium chlorate.

Chitosan (CTS), a biologically safe preservative, is crucial for post-harvest treatment of fruit and vegetables, yet its regulatory mechanisms remain poorly understood. Our research on various CTS concentrations in longan fruit post-harvest showed that 1.5% CTS curtailed Weight loss and malondialdehyde content while enhancing soluble solid content, carotenoids, ascorbic acid, total phenols, and flavonoids. Transcript-level analysis revealed that 1.5% CTS maintains longan fruit quality by modulating energy and amino acid metabolism pathways. Further evaluations demonstrated increased energy charge, adenosine triphosphate (ATP), and adenosine diphosphate (ADP) levels, alongside elevated activities of H⁺-ATPase, Ca²⁺-ATPase, cytochrome C oxidase, and succinate dehydrogenase in CTS-treated fruit. CTS also upregulated genes like H ⁺ -ATPase1, SDH1, SDH6, CCO5b-2, and CCO6b-2, boosted proline content, and enhanced activities of proline-metabolizing enzymes Δ1-pyrroline-5-carboxylic acid synthase (P5CS) and ornithine-ծ-aminotransferase (OAT), while reducing pyruvate dehydrogenase (PDH) activity. These results suggest that CTS effectively modulates gene expression and enzymatic functions related to energy and proline metabolism, enhancing the preservation of longan fruit freshness during storage.