Fatty acid synthesis is inhibited by inefficient utilization of unusual fatty acids for glycerolipid assembly
Fatty acid synthesis is inhibited by inefficient utilization of unusual fatty acids for glycerolipid assembly
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DOI：
10.1073/pnas.1318511111
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发表时间：
2014-01-21
影响因子：
11.1
通讯作者：
Browse, John
中科院分区：
文献类型：
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作者：
Bates, Philip D.;Johnson, Sean R.;Browse, John
长期以来，转基因植物通过β -氧化降解不寻常脂肪酸一直被假设为限制在种子油中生产工业上有用的不寻常脂肪酸的主要因素。表达蓖麻脂肪酸羟化酶的拟南芥种子在三酰甘油中积累的羟基化脂肪酸占总脂肪酸的17%；然而，总种子油也减少了50%。通过对发育中的种子进行体内[C-14]醋酸盐和[H-3](2)O代谢标记，对减少油表型的原因进行了调查，令人惊讶的是，转基因种子内的从头脂肪酸合成率大约是对照种子的一半。RNAseq分析显示，在羟化酶表达的植物中，脂肪酸合成基因的表达没有变化。然而，对表达羟化酶的种子进行[C-14]醋酸盐和[C-14]丙二酸盐代谢标记的差异表明，体内乙酰辅酶a羧化酶活性降低到对照种子的大约一半。因此，转基因种子含油量的降低与质体中脂肪酸合成的减少一致，而不是脂肪酸的降解。有趣的是，蓖麻三酰基甘油合成同工酶与脂肪酸羟化酶的共表达缓解了乙酰辅酶a羧化酶活性的降低，恢复了脂肪酸合成的速度，并大大恢复了种子油的积累。综上所述，这些结果表明了一种以前未被发现的机制，即检测内质网中不寻常脂肪酸的低效利用，并激活内源性途径，以减少质体内脂肪酸合成的翻译后减少。
Degradation of unusual fatty acids through beta-oxidation within transgenic plants has long been hypothesized as a major factor limiting the production of industrially useful unusual fatty acids in seed oils. Arabidopsis seeds expressing the castor fatty acid hydroxylase accumulate hydroxylated fatty acids up to 17% of total fatty acids in seed triacylglycerols; however, total seed oil is also reduced up to 50%. Investigations into the cause of the reduced oil phenotype through in vivo [C-14] acetate and [H-3](2)O metabolic labeling of developing seeds surprisingly revealed that the rate of de novo fatty acid synthesis within the transgenic seeds was approximately half that of control seeds. RNAseq analysis indicated no changes in expression of fatty acid synthesis genes in hydroxylase-expressing plants. However, differential [C-14] acetate and [C-14] malonate metabolic labeling of hydroxylase-expressing seeds indicated the in vivo acetyl-CoA carboxylase activity was reduced to approximately half that of control seeds. Therefore, the reduction of oil content in the transgenic seeds is consistent with reduced de novo fatty acid synthesis in the plastid rather than fatty acid degradation. Intriguingly, the coexpression of triacylglycerol synthesis isozymes from castor along with the fatty acid hydroxylase alleviated the reduced acetyl-CoA carboxylase activity, restored the rate of fatty acid synthesis, and the accumulation of seed oil was substantially recovered. Together these results suggest a previously unidentified mechanism that detects inefficient utilization of unusual fatty acids within the endoplasmic reticulum and activates an endogenous pathway for posttranslational reduction of fatty acid synthesis within the plastid.