Abstract：
Low iron (Fe) bioavailability can limit the biosynthesis of Fe-containing proteins, which are especially abundant in photosynthetic organisms, thus negatively affecting global primary productivity. Understanding cellular coping mechanisms under Fe limitation is therefore of great interest. We surveyed the temporal responses of Chlamydomonas (Chlamydomonas reinhardtii) cells transitioning from an Fe-rich to an Fe-free medium to document their short and long-term adjustments. While slower growth, chlorosis and lower photosynthetic parameters are evident only after one or more days in Fe-free medium, the abundance of some transcripts, such as those for genes encoding transporters and enzymes involved in Fe assimilation, change within minutes, before changes in intracellular Fe content are noticeable, suggestive of a sensitive mechanism for sensing Fe. Promoter reporter constructs indicate a transcriptional component to this immediate primary response. With acetate provided as a source of reduced carbon, transcripts encoding respiratory components are maintained relative to transcripts encoding components of photosynthesis and tetrapyrrole biosynthesis, indicating metabolic prioritization of respiration over photosynthesis. In contrast to the loss of chlorophyll, carotenoid content is maintained under Fe limitation despite a decrease in the transcripts for carotenoid biosynthesis genes, indicating carotenoid stability. These changes occur more slowly, only after the intracellular Fe quota responds, indicating a phased response in Chlamydomonas, involving both primary and secondary responses during acclimation to poor Fe nutrition.
摘要：
低铁（Fe）生物利用度会限制含铁蛋白的生物合成，在光合生物中特别丰富，从而对全球初级生产力产生负面影响。因此，了解Fe限制下的细胞应对机制非常有趣。我们调查了衣藻（Chlamydomonasreinhardtii）细胞从富含铁的培养基过渡到无铁的培养基的时间响应，以记录其短期和长期调整。虽然增长缓慢，黄化和较低的光合参数仅在无铁培养基中一天或多天后才明显，丰富的一些成绩单，例如编码参与铁同化的转运蛋白和酶的基因，在几分钟内改变，在细胞内Fe含量明显变化之前，提示感应铁的敏感机制。启动子报告构建体指示该立即初级应答的转录组分。用乙酸盐作为还原碳源，编码呼吸成分的转录本相对于编码光合作用和四吡咯生物合成成分的转录本得以维持，表明呼吸的代谢优先于光合作用。与叶绿素的损失相反，类胡萝卜素含量保持在Fe限制下，尽管类胡萝卜素生物合成基因的转录物减少，表明类胡萝卜素的稳定性。这些变化发生得更慢，只有在细胞内铁配额响应后，表明衣藻的阶段性反应，涉及适应不良铁营养期间的主要和次要反应。
