Bibby T S, Mary I, Nield J, Partensky F, Barber J
Wolfson Laboratories, Biochemistry Building, Department of Biological Sciences, South Kensington Campus, Imperial College London, London SW7 2AZ, UK.
Nature. 2003 Aug 28;424(6952):1051-4. doi: 10.1038/nature01933.
Prochlorococcus, the most abundant genus of photosynthetic organisms, owes its remarkably large depth distribution in the oceans to the occurrence of distinct genotypes adapted to either low- or high-light niches. The pcb genes, encoding the major chlorophyll-binding, light-harvesting antenna proteins in this genus, are present in multiple copies in low-light strains but as a single copy in high-light strains. The basis of this differentiation, however, has remained obscure. Here we show that the moderate low-light-adapted strain Prochlorococcus sp. MIT 9313 has one iron-stress-induced pcb gene encoding an antenna protein serving photosystem I (PSI)--comparable to isiA genes from cyanobacteria--and a constitutively expressed pcb gene encoding a photosystem II (PSII) antenna protein. By comparison, the very low-light-adapted strain SS120 has seven pcb genes encoding constitutive PSI and PSII antennae, plus one PSI iron-regulated pcb gene, whereas the high-light-adapted strain MED4 has only a constitutive PSII antenna. Thus, it seems that the adaptation of Prochlorococcus to low light environments has triggered a multiplication and specialization of Pcb proteins comparable to that found for Cab proteins in plants and green algae.
原绿球藻是光合生物中数量最多的属，其在海洋中具有显著广泛的深度分布，这归因于出现了适应低光或高光生态位的不同基因型。该属中编码主要叶绿素结合光捕获天线蛋白的 pcb 基因，在低光菌株中以多拷贝形式存在，而在高光菌株中则为单拷贝。然而，这种分化的基础一直不明。在此我们表明，中度适应低光的原绿球藻菌株 Prochlorococcus sp. MIT 9313 有一个铁胁迫诱导的 pcb 基因，编码一种服务于光系统 I（PSI）的天线蛋白——类似于蓝细菌的 isiA 基因——以及一个组成型表达的 pcb 基因，编码一种光系统 II（PSII）天线蛋白。相比之下，极度适应低光的菌株 SS120 有七个编码组成型 PSI 和 PSII 天线的 pcb 基因，外加一个 PSI 铁调节的 pcb 基因，而适应高光的菌株 MED4 只有一个组成型 PSII 天线。因此，似乎原绿球藻对低光环境的适应引发了 Pcb 蛋白的倍增和特化，这与植物和绿藻中 Cab 蛋白的情况类似。
