Oilseeds produce abundant triacylglycerol (TAG) during seed maturation to fuel the establishment of photoautotrophism in the subsequent generation. Commonly, TAG contains 18-carbon polyunsaturated fatty acids (FA), but plants also produce oils with unique chemical properties highly desirable for industrial processes. Unfortunately, plants that produce such oils are poorly suited to agronomic exploitation, leading to a desire to reconstitute novel oil biosynthesis in crop plants. Here, we studied the production and incorporation of hydroxy-fatty acids (HFA) onto TAG in Arabidopsis (Arabidopsis thaliana) plants expressing the castor (Ricinus communis) FAH12 hydroxylase. One factor limiting HFA accumulation in these plants is the inefficient removal of HFA from the site of synthesis on phosphatidylcholine (PC). In Arabidopsis, lysophosphatidic acid acyltransferase (LPCAT) cycles FA to and from PC for modification. We reasoned that the castor LPCAT (RcLPCAT) would preferentially remove HFA from PC, resulting in greater incorporation onto TAG. However, expressing RcLPCAT in Arabidopsis expressing FAH12 alone (line CL37) or together with castor acyl:coenzyme A:diacylglycerol acyltransferase2 reduced HFA and total oil yield. Detailed analysis indicated that RcLPCAT reduced the removal of HFA from PC, possibly by competing with the endogenous LPCAT isozymes. Significantly, coexpressing RcLPCAT with castor phospholipid:diacylglycerol acyltransferase increased novel FA and total oil contents by transferring HFA from PC to diacylglycerol. Our results demonstrate that a detailed understanding is required to engineer modified FA production in oilseeds and suggest that phospholipase A2 enzymes rather than LPCAT mediate the highly efficient removal of HFA from PC in castor seeds.

油料种子在种子成熟过程中产生丰富的三酰甘油（TAG），以促进下一代光自养作用的建立。通常，TAG 含有 18 碳多不饱和脂肪酸 (FA)，但植物也会产生具有独特化学性质的油，这对于工业过程来说是非常理想的。不幸的是，产生这种油的植物不太适合农艺开发，导致人们希望在农作物中重建新的油生物合成。在这里，我们研究了表达蓖麻 ( Ricinus communis ) FAH12 羟化酶的拟南芥 ( Arabidopsis thaliana ) 植物中羟基脂肪酸 (HFA) 的产生和 TAG 掺入。限制这些植物中 HFA 积累的因素之一是从磷脂酰胆碱 (PC) 合成位点低效去除 HFA。在拟南芥中，溶血磷脂酸酰基转移酶 (LPCAT) 在 FA 与 PC 之间循环进行修饰。我们推断蓖麻 LPCAT (RcLPCAT) 会优先从 PC 中去除 HFA，从而更好地结合到 TAG 上。然而，在单独表达FAH12（品系CL37）或与蓖麻酰基：辅酶A：二酰基甘油酰基转移酶2一起表达FAH12的拟南芥中表达RcLPCAT会降低HFA和总油产量。详细分析表明，RcLPCAT 可能通过与内源 LPCAT 同工酶竞争，减少了 PC 中 HFA 的去除。值得注意的是，将 RcLPCAT 与蓖麻磷脂：二酰基甘油酰基转移酶共表达，通过将 HFA 从 PC 转移到二酰基甘油，增加了新型 FA 和总油含量。我们的结果表明，需要详细了解油籽中改性 FA 的生产，并表明磷脂酶 A2 而非 LPCAT 介导从蓖麻籽中高效去除 PC 中的 HFA。