Zalutskaya Zhanneta, Kharatyan Nina, Forchhammer Karl, Ermilova Elena
Laboratory of Adaptation in Microorganisms, Biological Faculty, Saint-Petersburg State University, Universitetskaya em. 7/9, 199034 Saint-Petersburg, Russia.
Department of Microbiology/Organismic Interactions, Faculty of Biology, University of Tübingen, Auf der Morgenstelle 28, 72,076 Tübingen, Germany.
Plant Sci. 2015 Nov;240:1-9. doi: 10.1016/j.plantsci.2015.08.019. Epub 2015 Aug 28.
In all examined organisms that have the PII signal transduction machinery, PII coordinates the central C/N anabolic metabolism. In green algae and land plants, PII is localized in the chloroplast and controls the L-arginine biosynthetic pathway pathway. To elucidate additional functions of PII in the model photosynthetic organism Chlamydomonas reinhardtii (CrPII), we generated and analyzed four strains, in which PII was strongly under-expressed by artificial microRNA (GLB1-amiRNA strains). In response to nitrogen deficiency, Chlamydomonas produces triacylglycerols (TAGs) that are accumulated in lipid bodies (LB). Quantification of LBs by confocal microscopy in four GLB1-amiRNA strains showed that reduced PII levels resulted in over-accumulation of LBs compared to their parental strains. Moreover, knock-down of PII caused also an increase in the total TAG level. We propose that the larger yields of TAG-filled LBs in N-starved GLB1-amiRNA cells can be attributed to the strain's depleted PII level and their inability to properly control acetyl-CoA carboxylase activity (ACCase). Together, our results imply that PII in Chlamydomonas negatively controls TAG accumulation in LBs during acclimation to nitrogen starvation of the alga.
在所有已检测的具有PII信号转导机制的生物体中，PII协调着中心碳/氮合成代谢。在绿藻和陆地植物中，PII定位于叶绿体并控制L-精氨酸生物合成途径。为了阐明PII在模式光合生物莱茵衣藻（CrPII）中的其他功能，我们构建并分析了四个品系，其中PII通过人工微小RNA被强烈下调表达（GLB1-amiRNA品系）。响应氮缺乏，衣藻产生三酰甘油（TAGs）并积累在脂质体（LB）中。通过共聚焦显微镜对四个GLB1-amiRNA品系中的脂质体进行定量分析表明，与它们的亲本品系相比，PII水平降低导致脂质体过度积累。此外，PII的敲低也导致总TAG水平增加。我们认为，在氮饥饿的GLB1-amiRNA细胞中，富含TAG的脂质体产量更高可归因于该品系PII水平降低以及它们无法适当控制乙酰辅酶A羧化酶活性（ACCase）。总之，我们的结果表明，衣藻中的PII在藻类适应氮饥饿期间对脂质体中TAG的积累起负调控作用。
