Tree peony (Paeonia rockii) is an excellent woody oilseed crop, known for its high α-linolenic acid (ALA, ~45%) content, which is of great value for human health. However, the mechanisms underlying this high-level ALA accumulation in tree peony seeds are poorly understood. In this study, we evaluated the dynamic changes in the lipidomic profile of P. rockii seeds during development. A total of 760 lipid molecules were identified in the P. rockii seeds, triacylglycerol (TAG) lipid molecules showed the highest abundance and diversity, both increasing over seed development. Particularly, ALA was the predominant fatty acid at the TAG sn-3 position. We further characterized two diacylglycerol acyltransferase (DGAT) genes and three phospholipid:diacylglycerol acyltransferase (PDAT) genes involved in the transfer of fatty acids to the TAG sn-3 position. Gene expression and subcellular localization analyses suggested that PrDGATs and PrPDATs may function as endoplasmic reticulum-localized proteins in seed TAG biosynthesis. In vitro functional complementation analysis showed different substrate specificities, with PrPDAT2 having a specific preference for ALA. Multiple biological assays demonstrated that PrDGAT1, PrDGAT2, PrPDAT1–2, and PrPDAT2 promote oil synthesis. Specifically, PrPDAT2 leads to preferential ALA in the oil. Our findings provide novel functional evidence of the role of PrDGAT1 and PrPDAT2, which are potential targets for increasing the ALA yield in tree peony and other oilseed crops.

中文翻译：

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综合脂质组学分析揭示了紫斑牡丹种子中高水平α-亚麻酸积累的机制

牡丹（Paeonia rockii）是一种优良的木本油料作物，以其高α-亚麻酸（ALA，~45%）含量而闻名，对人类健康具有重要价值。然而，人们对牡丹种子中这种高水平 ALA 积累的机制知之甚少。在这项研究中，我们评估了 P. rockii 种子在发育过程中脂质组学特征的动态变化。在 P. rockii 种子中总共鉴定了 760 个脂质分子，其中三酰甘油 (TAG) 脂质分子显示出最高的丰度和多样性，并且随着种子发育而增加。特别是，ALA 是 TAG sn-3 位点的主要脂肪酸。我们进一步鉴定了参与脂肪酸转移至 TAG sn-3 位点的两个二酰基甘油酰基转移酶 (DGAT) 基因和三个磷脂：二酰基甘油酰基转移酶 (PDAT) 基因。基因表达和亚细胞定位分析表明，PrDGAT 和 PrPDAT 可能在种子 TAG 生物合成中充当内质网定位蛋白。体外功能互补分析显示不同的底物特异性，PrPDAT2 对 ALA 有特定的偏好。多项生物测定表明 PrDGAT1、PrDGAT2、PrPDAT1-2 和 PrPDAT2 促进油合成。具体来说，PrPDAT2 会导致油中优先产生 ALA。我们的研究结果为 PrDGAT1 和 PrPDAT2 的作用提供了新的功能证据，它们是增加牡丹和其他油料作物中 ALA 产量的潜在目标。