Multiomics analysis identifies two MIKC²-type MADS-box genes that regulate triacylglycerol biosynthesis in Akebia...

Triacylglycerols (TGs) strongly influence the total oil content in Akebia trifoliata seeds. However, the genetic basis and corresponding regulatory mechanisms responsible for both the TG content and its components are poorly understood. In this study, we first profiled the composition of fatty acid chains across various TG species using available lipidomic data and observed substantial variations in relative content between the H543 and L2127 genotypes. Second, using transcriptomic analysis, we identified 307 and 109 potential candidate genes by differential expression analysis and weighted gene coexpression network analysis (WGCNA), respectively. Third, by integrating these results, we identified 16 candidate genes involved in TG metabolism, encoding 6 enzymes and 10 transcription factors (TFs). Finally, regulatory network analysis suggested that two MIKC²-type MADS-box TFs (AGL6_1 and SVP_1) regulate a gene encoding a putative lipid phosphatidate phosphatase (LPP) involved in the Kennedy pathway. Notably, one and two missense mutations were detected in AGL6_1 and SVP_1, respectively, in the high-oil genotype H543 compared with the reference genome as well as the low-oil genotype L2127. These mutations resulted in amino acid substitutions from Arg¹²³ to Lys¹²³ in AGL6_1, and from Asp¹⁵⁹ to Glu¹⁵⁹ and from Glu¹⁶² to Asp¹⁶² in SVP_1. In contrast, no missense mutations were detected in the LPP gene itself between the two genotypes. In conclusion, AGL6_1 and SVP_1 were identified as hub genes influencing TG content and composition. These findings pave the way for further elucidation of the detailed mechanism of TG metabolism and genetic improvement of oil content in A. trifoliata.