Benzoxazinoids (BXs) are tryptophan-derived indole metabolites and play a role in various physiological processes, such as auxin metabolism. Auxin is essential in the process of somatic embryogenesis (SE) in plants. In this study, we used bioinformatics, transcriptome data, exogenous treatment experiments, and qPCR analysis to study the evolutionary pattern of Bx genes in green plants, the regulatory mechanism of DlBx genes during early SE, and the effect of 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-one (DIMBOA) on the early SE in Dimocarpus longan Lour. The results showed that 27 putative DlBxs were identified in the longan genome; the Bx genes evolved independently in monocots and dicots, and the main way of gene duplication for the DlBx was tandem duplication (TD) and the DlBx were strongly constrained by purification selection during evolution. The transcriptome data indicated varying expression levels of DlBx during longan early SE, and most DlBxs responded to light, temperature, drought stress, and 2,4-dichlorophenoxyacetic acid (2,4-D) treatment; qRT-PCR results showed DlBx1, DlBx6g and DlBx6h were responsive to auxin, and treatment with 0.1mg/L DIMBOA for 9 days significantly upregulated the expression levels of DlBx1, DlBx3g, DlBx6c, DlBx6f, DlB6h, DlBx7d, DlBx8, and DlBx9b. The correlation analysis showed a significantly negative correlation between the expression level of DlBx1 and the endogenous IAA contents; DIMBOA significantly promoted the early SE and significantly changed the endogenous IAA content, and the IAA content increased significantly at the 9th day and decreased significantly at the 13th day. Therefore, the results suggested that DIMBOA indirectly promote the early SE by changing the endogenous IAA content via affecting the expression level of DlBx1 and hydrogen peroxide (H₂O₂) content in longan.

Methyl jasmonic acid (MeJA) is a vital phytohormone that plays a key role in plant growth and adaptation to various environmental stresses. In the present study, on the basis of the longan genome, we identified a total of seven versatile putative abscisic acid-insensitive genes, which are the key players in plant growth and stress response. On the basis of bioinformatics analysis, transcriptome data, exogenous treatment experiments, and RT-qPCR findings, a comprehensive evolutionary pattern of ABI genes in different plant species and the effect of different MeJA treatments during early somatic embryogenesis in D. longan was carried out. The phylogeny results revealed that the seven DlABI genes evolved independently in monocots and dicots, having high protein sequence similarity, especially with Arabidopsis ABI genes. The comparative findings of gene structure, motif prediction, and synteny analysis suggest that DlABI genes disperse mainly through duplication events rather than localized tandem repeats. Furthermore, the correlations among the expressions of DlABI genes propose that the organization of the cis-regulatory elements in the promoter regions may regulate the temporal and spatial transcription activation of these genes. The qRT-PCR results revealed that the 50 µM MeJA treatment significantly upregulated the expression of DlABI3, followed by DlABI1, DlABI2, DlABI5, DlABI4, and DlABI8, respectively. The ROS findings clearly revealed that MeJA distinctly elevated the SOD, POD, and H₂O₂ activities while reducing catalase and MDA contents. The subcellular localization of DlABI3 further confirmed its presence in the nucleus, suggesting its predicated transcriptional regulatory role in MeJA-mediated early SE in longan. Our findings reveal that the ABI genes are integral to the mechanism of MeJA-induced early somatic embryogenesis in longan by maintaining the ROS activity.

Dimocarpus longan Lour. is an evergreen tree of the genus Longan in the Sapindaceae family, native to tropical and subtropical regions. Longan embryonic development is closely related to fruit set and fruit quality. An in-depth study of the mechanism of longan embryonic development could therefore contribute to the development of the longan industry. DIMBOA is the principal compound representing benzoxazinoids (BXs), and is closely linked to auxin biosynthesis and signal transduction. Auxin is one of the crucial hormones for inducing somatic embryogenesis (SE) in plants. Previous research has shown that DIMBOA promotes morphogenesis in the early somatic embryogenesis of longan, but the specific regulatory mechanism has not yet been clarified. To elucidate the molecular mechanism by which DIMBOA affects early somatic embryogenesis in longan, we chose longan embryogenic cultures grown under 0 mg/L DIMBOA as the control group (the check, CK), and longan embryogenic cultures grown under 0.1 mg/L DIMBOA as the treatment group (D) to be analyzed by transcriptomic sequencing. A total of 478 differentially expressed genes (DEGs) are detected in check vs. D, of which 193 are upregulated and 285 are downregulated. These DEGs are significantly enriched in the biosynthetic and metabolic functions of various substances such as vitamin B₆ (VB₆) biosynthesis, phenylpropanoid pathways, and carbohydrate metabolism. DIMBOA affects SE processes in longan via TFs, including MYB, ZF, bHLH, LBD, NAC, WRKY, etc. After DIMBOA treatment, the expression of most of the key genes for IAA synthesis was significantly downregulated, VB₆ content was significantly reduced, and H₂O₂ content was significantly increased. Therefore, it is suggested that DIMBOA directly or indirectly affects the H₂O₂ content through the VB₆ metabolic pathway, thereby regulating the endogenous IAA level to modulate the early SE morphogenesis of longan.

PP2C (protein phosphatases 2C) are key regulators of abscisic acid (ABA) signaling that play a crucial role in plant stress responses. Our analysis identified 71 DlPP2C genes in Dimocarpus longan, which were classified into distinct subgroups based on phylogenetic relationships with Arabidopsis thaliana and Oryza sativa. Structural analysis demonstrated conserved motif composition and gene organization within subgroups, while chromosomal distribution and synteny analysis revealed that segmental duplication events contributed to the expansion of this gene family. Promoter analysis uncovered several cis-acting elements related to hormone and stress responsiveness, especially abscisic acid-responsive elements (ABREs), suggesting that DlPP2C genes may play a role in ABA signaling pathways. Furthermore, we examined the ABA-responsive expression profiles of DlPP2C genes under exogenous ABA treatments. The expression patterns were dynamic and dose- and time-dependent, with several genes showing peak expression at 10 μM ABA after 16 h. The DlPP2C1 in particular displayed a strong transcriptional response, indicating its potential role in ABA regulation. While overexpression and GUS staining assays revealed enhanced activity under ABA treatment, further supporting the involvement of PP2C in ABA-responsive regulation, further mechanistic studies are needed for a full characterization. Finally, RNA sequencing analysis revealed a total of 1799 differentially expressed genes in response to ABA, with a prevalence of downregulated genes, showing extensive transcriptional reprogramming. Functional enrichment analysis demonstrated that these genes were largely associated with plant hormone signaling, stress response, and metabolic pathways. Weighted gene co-expression network analysis revealed a total of 32 key gene modules associated with ABA signaling. Collectively, our findings propose that DlPP2C genes, especially DlPP2C1, play a key role in ABA-mediated regulatory networks and provide valuable insights into stress adaptation mechanisms, especially during early somatic embryogenesis in longan.

The PP2C (protein phosphates 2C) are key regulators of abscisic acid (ABA) signaling that play a crucial role in plant stress responses. In this study, we performed a comprehensive genome-wide analysis and identified 71 DlPP2C genes in Dimocarpus longan which is an economically important fruit crop. The evolutionary analysis revealed that DlPP2C genes were classified into distinct subgroups based on phylogenetic relationships with Arabidopsis thaliana and Oryza sativa. Structural analysis demonstrated conserved motif composition and gene organization within subgroups, whereas chromosomal distribution and synteny analysis revealed that segmental duplication events contributed to gene family expansion. Promoter analysis findings identified numerous cis-acting elements related to hormone and stress responsiveness especially abscisic acid-responsive elements (ABREs), suggesting their potential involvement in ABA signaling pathways. Under exogenous ABA treatments, expression profiling of the DlPP2C genes exhibited dynamic, dose and time dependent response with several genes showing peak expression at 10 μM ABA after 16 h, especially the DlPP2C1 displayed a strong transcriptional response, indicating its potential role as a key regulator. Overexpression and GUS staining assays revealed enhanced activity under ABA treatment, further supporting its involvement in ABA-responsive regulation. Moreover, RNA sequencing analysis revealed a total of 1799 differentially expressed genes, with prevalence of downregulated genes, showing extensive transcriptional reprograming. Functional enrichment analysis demonstrated that these genes were largely associated with plant hormone signaling, stress response and metabolic pathways. Together, these findings propose that DlPP2C genes, especially DlPP2C1, play a key role in ABA-mediated regulatory networks and provide valuable insights intro stress adaption mechanisms during early somatic embryogenesis in longan.

Dwarfing is one of the common phenotypic variations in asexually reproduced progeny of banana, and dwarfed banana is not only windproof and anti-fallout but also effective in increasing acreage yield. As a key gene in the strigolactone signalling pathway, DWARF53 (D53) plays an important role in the regulation of the height of plants. In order to gain insight into the function of the banana D53 gene, this study conducted genome-wide identification of banana D53 gene based on the M. acuminata, M. balbisiana and M. itinerans genome database. Analysis of MaD53 gene expression under high temperature, low temperature and osmotic stress based on transcriptome data and RT-qPCR was used to analyse MaD53 gene expression in different tissues as well as in different concentrations of GA and SL treatments. In this study, we identified three MaD53, three MbD53 and two MiD53 genes in banana. Phylogenetic tree analysis showed that D53 Musa are equally related to D53 Asparagales and Poales. Both high and low-temperature stresses substantially reduced the expression of the MaD53 gene, but osmotic stress treatments had less effect on the expression of the MaD53 gene. GR24 treatment did not significantly promote the height of the banana, but the expression of the MaD53 gene was significantly reduced in roots and leaves. GA treatment at 100 mg/L significantly promoted the expression of the MaD53 gene in roots, but the expression of this gene was significantly reduced in leaves. In this study, we concluded that MaD53 responds to GA and SL treatments, but “Yinniaijiao” dwarf banana may not be sensitive to GA and SL.