A Galactoglycerolipid Lipase Is Required for Triacylglycerol Accumulation and Survival Following Nitrogen Deprivation in Chlamydomonas reinhardtii
A Galactoglycerolipid Lipase Is Required for Triacylglycerol Accumulation and Survival Following Nitrogen Deprivation in Chlamydomonas reinhardtii
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DOI：
10.1105/tpc.112.105106
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发表时间：
2012-11-01
期刊：
影响因子：
11.6
通讯作者：
Benning, Christoph
中科院分区：
文献类型：
--
作者：
Li, Xiaobo;Moellering, Eric R.;Benning, Christoph
在N剥夺之后，微藻积累三酰基甘油（TAG）。为了获得对这一现象的机理的见解，我们确定了在模型莱茵衣藻中N剥夺后TAG含量降低的突变体。在其中一个突变体中，半乳糖甘油酯脂肪酶编码基因（命名为质体半乳糖甘油酯降解1（PGD1））的破坏导致了主要表型：TAG含量降低、TAG组成改变和半乳糖甘油酯周转率降低。从大肠杆菌提取物中纯化的重组PGD1蛋白水解单半乳糖基二酰甘油成其溶血脂质衍生物。在体内脉冲追踪标记确定半乳糖甘油脂池作为脂肪酸酯化的TAG后N剥夺的主要来源。此外，在pgd1突变体中，从质体脂质到TAG的脂肪酸通量降低。显然，莱茵衣藻中重新合成的脂肪酸在进入TAG合成之前，至少部分地首先掺入质体脂质中。作为一个次要的影响，pgd1突变体表现出的活力损失后，N剥夺，这可以避免通过阻止光合电子传递。因此，pgd1突变体提供了证据的一个重要的生物功能的TAG合成后N剥夺，即减轻有害的过度还原的光合电子传递链。
Following N deprivation, microalgae accumulate triacylglycerols (TAGs). To gain mechanistic insights into this phenomenon, we identified mutants with reduced TAG content following N deprivation in the model alga Chlamydomonas reinhardtii. In one of the mutants, the disruption of a galactoglycerolipid lipase-encoding gene, designated PLASTID GALACTOGLYCEROLIPID DEGRADATION1 (PGD1), was responsible for the primary phenotype: reduced TAG content, altered TAG composition, and reduced galactoglycerolipid turnover. The recombinant PGD1 protein, which was purified from Escherichia coli extracts, hydrolyzed monogalactosyldiacylglycerol into its lyso-lipid derivative. In vivo pulse-chase labeling identified galactoglycerolipid pools as a major source of fatty acids esterified in TAGs following N deprivation. Moreover, the fatty acid flux from plastid lipids to TAG was decreased in the pgd1 mutant. Apparently, de novo-synthesized fatty acids in Chlamydomonas reinhardtii are, at least partially, first incorporated into plastid lipids before they enter TAG synthesis. As a secondary effect, the pgd1 mutant exhibited a loss of viability following N deprivation, which could be avoided by blocking photosynthetic electron transport. Thus, the pgd1 mutant provides evidence for an important biological function of TAG synthesis following N deprivation, namely, relieving a detrimental overreduction of the photosynthetic electron transport chain.