Voss Björn, Meinecke Linda, Kurz Thorsten, Al-Babili Salim, Beck Christoph F, Hess Wolfgang R
Faculty of Biology, Institute of Biology III , University of Freiburg, D-79104 Freiburg, Germany.
Plant Physiol. 2011 Feb;155(2):892-905. doi: 10.1104/pp.110.158683. Epub 2010 Dec 9.
Retrograde signaling is a pathway of communication from mitochondria and plastids to the nucleus in the context of cell differentiation, development, and stress response. In Chlamydomonas reinhardtii, the tetrapyrroles magnesium-protoporphyrin IX and heme are only synthesized within the chloroplast, and they have been implicated in the retrograde control of nuclear gene expression in this unicellular green alga. Feeding the two tetrapyrroles to Chlamydomonas cultures was previously shown to transiently induce five nuclear genes, three of which encode the heat shock proteins HSP70A, HSP70B, and HSP70E. In contrast, controversial results exist on the possible role of magnesium-protoporphyrin IX in the repression of genes for light-harvesting proteins in higher plants, raising the question of how important this mode of regulation is. Here, we used genome-wide transcriptional profiling to measure the global impact of these tetrapyrroles on gene regulation and the scope of the response. We identified almost 1,000 genes whose expression level changed transiently but significantly. Among them were only a few genes for photosynthetic proteins but several encoding enzymes of the tricarboxylic acid cycle, heme-binding proteins, stress-response proteins, as well as proteins involved in protein folding and degradation. More than 50% of the latter class of genes was also regulated by heat shock. The observed drastic fold changes at the RNA level did not correlate with similar changes in protein concentrations under the tested experimental conditions. Phylogenetic profiling revealed that genes of putative endosymbiontic origin are not overrepresented among the responding genes. This and the transient nature of changes in gene expression suggest a signaling role of both tetrapyrroles as secondary messengers for adaptive responses affecting the entire cell and not only organellar proteins.
逆行信号传导是在细胞分化、发育和应激反应过程中，从线粒体和质体到细胞核的一种通讯途径。在莱茵衣藻中，四吡咯镁原卟啉IX和血红素仅在叶绿体内合成，并且它们与这种单细胞绿藻中核基因表达的逆行调控有关。先前的研究表明，将这两种四吡咯添加到莱茵衣藻培养物中会短暂诱导五个核基因，其中三个编码热休克蛋白HSP70A、HSP70B和HSP70E。相比之下，关于镁原卟啉IX在高等植物中对光捕获蛋白基因的抑制作用，存在有争议的结果，这就引发了这种调控模式有多重要的问题。在这里，我们使用全基因组转录谱分析来测量这些四吡咯对基因调控的全局影响以及反应的范围。我们鉴定出近1000个基因，其表达水平发生了短暂但显著的变化。其中只有少数是光合蛋白基因，但有几个编码三羧酸循环的酶、血红素结合蛋白、应激反应蛋白以及参与蛋白质折叠和降解的蛋白。后一类基因中超过50%也受热休克调控。在测试的实验条件下，RNA水平上观察到的剧烈倍数变化与蛋白质浓度的类似变化不相关。系统发育谱分析表明，推定的内共生起源基因在响应基因中并不占优势。基因表达变化的这种性质以及其短暂性表明，这两种四吡咯作为二级信使，在影响整个细胞而非仅细胞器蛋白的适应性反应中发挥信号传导作用。
