Gene-Metabolite Network Analysis Revealed Tissue-Specific Accumulation of Therapeutic Metabolites in Mallotus japonicus

Mallotus japonicus is a valuable traditional medicinal plant in East Asia for applications as a gastrointestinal drug. However, the molecular components involved in the biosynthesis of bioactive metabolites have not yet been explored, primarily due to a lack of omics resources. In this study, we established metabolome and transcriptome resources for M. japonicus to capture the diverse metabolite constituents and active transcripts involved in its biosynthesis and regulation. A combination of untargeted metabolite profiling with data-dependent metabolite fragmentation and metabolite annotation through manual curation and feature-based molecular networking established an overall metabospace of M. japonicus represented by 2129 metabolite features. M. japonicus de novo transcriptome assembly showed 96.9% transcriptome completeness, representing 226,250 active transcripts across seven tissues. We identified specialized metabolites biosynthesis in a tissue-specific manner, with a strong correlation between transcripts expression and metabolite accumulations in M. japonicus. The correlation- and network-based integration of metabolome and transcriptome datasets identified candidate genes involved in the biosynthesis of key specialized metabolites of M. japonicus. We further used phylogenetic analysis to identify 13 C-glycosyltransferases and 11 methyltransferases coding candidate genes involved in the biosynthesis of medicinally important bergenin. This study provides comprehensive, high-quality multi-omics resources to further investigate biological properties of specialized metabolites biosynthesis in M. japonicus.

Xylan deposition and lignification in differentiating tension wood fibers in Mallotus japonicus (Euphorbiaceae) with multi-layered structure

Xylan deposition and lignification processes were examined in tension wood fibers with gelatinous layers (G-layers) in Mallotus japonicus (Euphorbiaceae). The cell walls consisted of a multi-layered structure of S1 + S2 + G + n(L + G), where n indicates the number of repetitions (n = 0–3) and L indicates very thin lignified layers. The formation and lignification processes of the multi-layered structure of tension wood fibers were examined by light microscopy, ultraviolet microscopy, and transmission electron microscopy (TEM) following KMnO4 staining. The deposition of xylan was examined by immunoelectron microscopy with a monoclonal antibody (LM11). Immunolabelling of xylan appeared in lignified cell wall layers, except in the compound middle lamella (CML), i.e., the S1, S2, and L layers but not the G-layers. The density of LM11 xylan immunogold labeling in S2 layers increased during the formation of G-layers. This increase was due to the shrinkage of S2 layers during development rather than intrusive deposition of xylan through G-layers. Lignification of the CML, S1, and S2 layers proceeded during G-layer formation. The shrinkage of S2 layers occurred almost simultaneously with the lignification of the S2 layers during G-layer formation, suggesting that the S2 layers shrank with lignification.

An Antiproliferative ent-Kaurane Diterpene Isolated from the Roots of Mallotus japonicus Induced Apoptosis in Leukemic Cells

Mallotus japonicus has been evaluated for the treatment of dermatitis, inflammatory conditions, and cancer. Diterpenes, one of the major constituents of M. japonicus, possess various pharmacological effects. In this study, 2 known diterpenes, anomaluone (6) and 16-epiabbeokutone (7), along with other known compounds, 2-hydroxy ferulic acid (1), bergenin (2), gallocatechin (3), catechin (4), erythro,erythro-1-[4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-(hydroxymethyl) ethoxy]-3,5-dimethoxyphenyl]-1,2,3- propanetriol (5), and gallincin (8), were isolated from M. japonicus. Cytotoxicity assays in blood cancer cell models demonstrated that M. japonicus compounds possess potent antiproliferative activity. In addition, treatment with compound 6 increased the number of apoptotic cells, led to cell-cycle arrest at the subG0/G1 phase, and decreased the number of cells in the S and G2/M phases. Compound 6 also displayed potent mitochondrial depolarization effects in Jurkat cells. These findings revealed that the cytotoxic effects of 6 were mediated by intracellular signaling, possibly through a mechanism involving upregulation of mitochondrial reactive oxygen species. Thus, compound 6 could be a potential multi-target therapeutic agent for leukemia.