Teshima Takuya, Nemoto Keiichirou, Shimizu Motoki, Yoshida Chiharu, Hirabuchi Akiko, Goto Fumina, Nakasato Takashi, Naito Zenbi, Nishihara Masahiro
Iwate Biotechnology Research Center, 22-174-4 Narita, Kitakami, Iwate, 024-0003, Japan.
Iwate Agricultural Research Center, 22-1 Narita, Kitakami, Iwate, 024-0003, Japan.
Planta. 2025 Jul 23;262(3):62. doi: 10.1007/s00425-025-04772-4.
This study identified GeBCAT2 as a key gene in catalyzing the first step of branched chain amino acid biosynthesis in Gentiana triflora, thereby contributing to unpleasant floral odor emission. Gentians, widely cultivated as ornamental flowers in Japan, primarily originate from the endemic gentian species Gentiana triflora and G. scabra. This study analyzed volatile compounds in Japanese gentians using gas chromatography-mass spectrometry. Results showed that G. triflora flowers consistently emitted 3-methylbutanoic acid, 2-methylbutanoic acid, and isobutyric acid, which are volatile organic compounds derived from branched-chain amino acids (BCAAs) and associated with unpleasant odors. In contrast, G. scabra flowers did not emit these compounds. Although the BCAA metabolism has been widely studied, its catabolic pathways in gentians remain unclear. Therefore, we performed precursor feeding experiments to quantitatively verify the role of BCAAs and their corresponding keto acids in producing odorous volatiles. We also cloned and functionally analyzed two Gentiana BCAAs transferase genes (GeBCAT1 and GeBCAT2). Both genes were more highly expressed in flowers than in leaves, with expression levels higher in G. triflora than in G. scabra. Enzymatic assays with recombinant proteins demonstrated that GeBCAT1 and GeBCAT2 participate in BCAA-related catabolic reactions. Notably, GeBCAT2's substrate specificity for BCAAs correlated with unpleasant odor intensity in G. triflora, suggesting that it serves as the primary enzyme initiating unpleasant odor biosynthesis in gentians. These findings provide valuable insights into volatile biosynthesis in gentians and offer a foundation for breeding cultivars with reduced unpleasant odors.
本研究确定了GeBCAT2是三花龙胆中催化支链氨基酸生物合成第一步的关键基因，从而导致了令人不悦的花香排放。龙胆在日本作为观赏花卉广泛种植，主要源自本土龙胆物种三花龙胆和粗糙龙胆。本研究使用气相色谱 - 质谱联用技术分析了日本龙胆中的挥发性化合物。结果表明，三花龙胆花持续释放3 - 甲基丁酸、2 - 甲基丁酸和异丁酸，这些是源自支链氨基酸（BCAAs）的挥发性有机化合物，与令人不悦的气味相关。相比之下，粗糙龙胆花不释放这些化合物。尽管BCAA代谢已被广泛研究，但其在龙胆中的分解代谢途径仍不清楚。因此，我们进行了前体饲喂实验，以定量验证BCAAs及其相应酮酸在产生有气味挥发物中的作用。我们还克隆并对两个龙胆BCAAs转移酶基因（GeBCAT1和GeBCAT2）进行了功能分析。这两个基因在花中的表达均高于叶，且在三花龙胆中的表达水平高于粗糙龙胆。对重组蛋白的酶活性测定表明，GeBCAT1和GeBCAT2参与与BCAA相关的分解代谢反应。值得注意的是，GeBCAT2对BCAAs的底物特异性与三花龙胆中令人不悦气味的强度相关，这表明它是龙胆中引发令人不悦气味生物合成的主要酶。这些发现为龙胆中的挥发性生物合成提供了有价值的见解，并为培育气味较淡的品种奠定了基础。
