Synergism between Inositol Polyphosphates and TOR Kinase Signaling in Nutrient Sensing, Growth Control, and Lipid Metabolism in Chlamydomonas
Synergism between Inositol Polyphosphates and TOR Kinase Signaling in Nutrient Sensing, Growth Control, and Lipid Metabolism in Chlamydomonas
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DOI：
10.1105/tpc.16.00351
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发表时间：
2016-09-01
期刊：
影响因子：
11.6
通讯作者：
Umen, James G.
中科院分区：
文献类型：
--
作者：
Couso, Inmaculada;Evans, Bradley S.;Umen, James G.
在光合作用细胞中，控制碳代谢和控制细胞内碳分配的网络知之甚少。雷帕霉素靶蛋白激酶（TOR）是一种保守的生长调节因子，在真核生物中整合营养信号并调节细胞生长，但植物和藻类中TOR信号通路的研究还不完全清楚。我们使用插入诱变筛选单细胞绿色莱茵衣藻，以发现赋予TOR抑制剂雷帕霉素超敏性的突变体。我们鉴定了一个突变体vip 1 -1，该突变体被预测编码来自VIP家族的保守肌醇六磷酸激酶，该激酶焦磷酸化植酸（InsP（6））以产生低丰度信号分子InsP（7）和InsP（8）。出乎意料的是，vip 1 -1细胞的雷帕霉素超敏生长停滞依赖于外部乙酸盐的存在，其通常对衣原体具有生长刺激作用。vip 1 -1突变体也以与其它TAG诱导刺激如饥饿协同的方式组成性过度积累三酰基甘油（TAG）。vip 1 -1细胞具有减少的InsP（7）和InsP（8），这两者在野生型细胞中通过TOR激酶活性和乙酸盐的存在而动态调节。我们的数据揭示了TOR激酶和肌醇多磷酸信号传导系统之间的相互作用，我们提出控制碳代谢和细胞内途径，导致储存脂质积累。
The networks that govern carbon metabolism and control intracellular carbon partitioning in photosynthetic cells are poorly understood. Target of Rapamycin (TOR) kinase is a conserved growth regulator that integrates nutrient signals and modulates cell growth in eukaryotes, though the TOR signaling pathway in plants and algae has yet to be completely elucidated. We screened the unicellular green alga Chlamydomonas reinhardtii using insertional mutagenesis to find mutants that conferred hypersensitivity to the TOR inhibitor rapamycin. We characterized one mutant, vip1-1, that is predicted to encode a conserved inositol hexakisphosphate kinase from the VIP family that pyrophosphorylates phytic acid (InsP(6)) to produce the low abundance signaling molecules InsP(7) and InsP(8). Unexpectedly, the rapamycin hypersensitive growth arrest of vip1-1 cells was dependent on the presence of external acetate, which normally has a growth-stimulatory effect on Chlamydomonas. vip1-1 mutants also constitutively overaccumulated triacylglycerols (TAGs) in a manner that was synergistic with other TAG inducing stimuli such as starvation. vip1-1 cells had reduced InsP(7) and InsP(8), both of which are dynamically modulated in wild-type cells by TOR kinase activity and the presence of acetate. Our data uncover an interaction between the TOR kinase and inositol polyphosphate signaling systems that we propose governs carbon metabolism and intracellular pathways that lead to storage lipid accumulation.