School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan; Graduate School of Integrated Sciences for Life, Hiroshima University, 1-4-3, Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
School of Life Science and Technology, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
Biochim Biophys Acta Mol Cell Biol Lipids. 2019 Sep;1864(9):1185-1193. doi: 10.1016/j.bbalip.2019.05.013. Epub 2019 May 30.
Organisms of the microalgal genus Nannochloropsis produce high levels of triacylglycerols (TAGs), an efficient raw material for biofuels. A complete understanding of the TAG-breakdown pathway is critical for improving the productivity of TAGs to meet future needs. Among a number of lipases annotated as TAG lipase in the genomes of every organism, Arabidopsis SUGAR-DEPENDENT 1 (AtSDP1) lipases are characterized as a type of crucial TAG lipase in plants, similar to ScTgl3-5 in Saccharomyces cerevisiae. Homologs of the AtSDP1 TAG lipases are universally found in the genomes of plants, fungi, and algae. Here we identified two homologs of AtSDP1 TAG lipases in the oleaginous microalga species Nannochloropsis oceanica, NoTGL1 and NoTGL2. We generated single- and double-knockout strains for these lipases by homologous recombination. Whereas overall TAG content in the NoTGL2 single-knockout mutant was identical to that of wild type, the NoTGL1 knockout showed a two-fold increase in TAG content per cell in early log phase under nutrient-sufficient conditions without affecting growth. Homologs of AtSDP1 in S. cerevisiae are localized to the surface of lipid droplets, and AtSDP1 is transported from peroxisomes to the surface of lipid droplets. In contrast, NoTGL1 localized to the endoplasmic reticulum in both Nannochloropsis and yeast. We suggest that homologs of AtSDP1 lipases in Nannochloropsis modulate de novo TAG biosynthesis in the endoplasmic reticulum, unlike the roles of these lipases in other organisms. These results provide important insights into the mechanisms of TAG metabolism catalyzed by homologs of AtSDP1 lipase, which are highly conserved across species.
微藻属拟球藻（Nannochloropsis）生物体能高效合成三酰基甘油(TAGs)，而 TAGs 是生物燃料的理想原料。全面了解 TAG 分解途径对于提高 TAG 产量以满足未来需求至关重要。在每种生物体基因组中注释的许多脂肪酶中，拟南芥糖依赖性 1（Arabidopsis SUGAR-DEPENDENT 1，AtSDP1）脂肪酶被认为是植物中一种重要的 TAG 脂肪酶，类似于酿酒酵母中的 ScTgl3-5。AtSDP1 TAG 脂肪酶的同源物普遍存在于植物、真菌和藻类的基因组中。在这里，我们在产油微藻物种海洋拟球藻（Nannochloropsis oceanica）中鉴定到了两个 AtSDP1 TAG 脂肪酶的同源物，NoTGL1 和 NoTGL2。我们通过同源重组生成了这些脂肪酶的单敲除和双敲除突变株。虽然 NoTGL2 单敲除突变体的总 TAG 含量与野生型相同，但在营养充足的条件下，NoTGL1 敲除突变体在对数早期每个细胞的 TAG 含量增加了两倍，而不影响生长。酿酒酵母中 AtSDP1 的同源物定位于脂滴的表面，并且 AtSDP1 从过氧化物酶体转运到脂滴的表面。相比之下，NoTGL1 在 Nannochloropsis 和酵母中均定位于内质网。我们认为，拟南芥 AtSDP1 脂肪酶的同源物在 Nannochloropsis 中调节内质网中新的 TAG 生物合成，而不是在其他生物体中发挥作用。这些结果为 AtSDP1 脂肪酶同源物催化的 TAG 代谢机制提供了重要的见解，这些机制在物种间高度保守。
