Howard Hughes Medical Institute, University of California, Berkeley, CA 94720.
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2017 Apr 25;114(17):4537-4542. doi: 10.1073/pnas.1700139114. Epub 2017 Apr 10.
Aquatic photosynthetic organisms cope with low environmental CO concentrations through the action of carbon-concentrating mechanisms (CCMs). Known eukaryotic CCMs consist of inorganic carbon transporters and carbonic anhydrases (and other supporting components) that culminate in elevated [CO] inside a chloroplastic Rubisco-containing structure called a pyrenoid. We set out to determine the molecular mechanisms underlying the CCM in the emerging model photosynthetic stramenopile, , a unicellular picoplanktonic alga that lacks a pyrenoid. We characterized () as an essential component of the CCM in CCMP1779. We generated insertions in this gene by directed homologous recombination and found that the mutant has severe defects in growth and photosynthesis at ambient CO We identified CAH1 as an α-type carbonic anhydrase, providing a biochemical role in CCM function. CAH1 was found to localize to the lumen of the epiplastid endoplasmic reticulum, with its expression regulated by the external inorganic carbon concentration at both the transcript and protein levels. Taken together, these findings show that is an indispensable component of what may be a simple but effective and dynamic CCM in .
水生光合生物通过碳浓缩机制 (CCM) 来应对环境中低浓度的 CO2。已知的真核生物 CCM 由无机碳转运蛋白和碳酸酐酶（和其他支持成分）组成，最终在一个含有 Rubisco 的叶绿体类囊体结构内使 [CO2] 升高，这个结构被称为淀粉核。我们着手确定新兴的光合甲藻模式生物 中的 CCM 的分子机制，它是一种缺乏淀粉核的单细胞微微型浮游藻类。我们确定 () 是 CCMP1779 中 CCM 的必需组成部分。我们通过定向同源重组生成了这个基因的插入突变体，发现 突变体在环境 CO2 下的生长和光合作用严重受损。我们鉴定了 CAH1 是一种 α 型碳酸酐酶，为 CCM 功能提供了生化作用。CAH1 被发现定位于质体外膜内质网的腔中，其表达在转录和蛋白水平上都受到外部无机碳浓度的调节。综上所述，这些发现表明 是可能是简单但有效和动态的 CCM 的不可或缺的组成部分。
