Expression of a Low CO2-Inducible Protein, LCI1, Increases Inorganic Carbon Uptake in the Green Alga Chlamydomonas reinhardtii
Expression of a Low CO2-Inducible Protein, LCI1, Increases Inorganic Carbon Uptake in the Green Alga Chlamydomonas reinhardtii
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DOI：
10.1105/tpc.109.071811
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发表时间：
2010-09-01
期刊：
影响因子：
11.6
通讯作者：
Fukuzawa, Hideya
中科院分区：
文献类型：
--
作者：
Ohnishi, Norikazu;Mukherjee, Bratati;Fukuzawa, Hideya
水生光合生物可以通过诱导碳浓缩机制（CCM）来调节其光合作用以适应CO2限制胁迫，该机制包括碳酸酐酶和无机碳（Ci）转运蛋白。然而，到目前为止，Ci特异性转运蛋白在真核藻类中还没有得到很好的表征。以前，一个衣原体reinhardtii突变体（lcr 1）被确定为缺少一个Myb转录因子。该突变体在CO2限制条件下生长时具有降低的光依赖性CO2气体交换（LCE）活性，并且不诱导编码周质碳酸酐酶的CAH 1基因以及两个尚未表征的基因LCI 1和LCI 6。在这项研究中，LCI 1被置于硝酸还原酶启动子的控制下，允许在没有其他CCM组分的情况下通过硝酸盐诱导LCI 1表达。当LCI 1的表达诱导在LCR 1突变体在CO2富集条件下，细胞表现出增加LCE活性，内部Ci积累，和光合亲和力Ci。从使用间接免疫荧光、LCI 1-绿色荧光蛋白融合和细胞分级分离程序的实验中，似乎LCI 1主要定位于质膜。这些结果提供了强有力的证据表明，LCI 1可能有助于CCM作为一个组成部分的Ci运输机械质膜。
Aquatic photosynthetic organisms can modulate their photosynthesis to acclimate to CO2-limiting stress by inducing a carbon-concentrating mechanism (CCM) that includes carbonic anhydrases and inorganic carbon (Ci) transporters. However, to date, Ci-specific transporters have not been well characterized in eukaryotic algae. Previously, a Chlamydomonas reinhardtii mutant (lcr1) was identified that was missing a Myb transcription factor. This mutant had reduced light-dependent CO2 gas exchange (LCE) activity when grown under CO2-limiting conditions and did not induce the CAH1 gene encoding a periplasmic carbonic anhydrase, as well as two as yet uncharacterized genes, LCI1 and LCI6. In this study, LCI1 was placed under the control of the nitrate reductase promoter, allowing for the induction of LCI1 expression by nitrate in the absence of other CCM components. When the expression of LCI1 was induced in the lcr1 mutant under CO2-enriched conditions, the cells showed an increase in LCE activity, internal Ci accumulation, and photosynthetic affinity for Ci. From experiments using indirect immunofluorescence, LCI1-green fluorescent protein fusions, and cell fractionation procedures, it appears that LCI1 is mainly localized to the plasma membrane. These results provide strong evidence that LCI1 may contribute to the CCM as a component of the Ci transport machinery in the plasma membrane.