Zhao Fangqing, Qin Song
Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, China.
Genetica. 2007 Mar;129(3):291-9. doi: 10.1007/s10709-006-0010-9. Epub 2006 Aug 8.
As the only remainder type of phycobiliproteins in Prochlorococcus, the actual role of phycoerythrin still remains unknown. Previous studies revealed that two different forms of phycoerythrin gene were found in two ecotypes of Prochlorococcus that are specifically adapted to either high light (HL) or low light (LL) conditions. Here we analyze patterns of phycoerythrin nucleotide variation in the HL- and LL-Prochlorococcus populations. Our analyses reveal a significantly greater number of non-synonymous fixed substitutions in peB and peA than expected based on interspecific comparisons. This pattern of excess non-synonymous fixed substitutions is not seen in other five phycoerythrin-related genes (peZ/V/Y/T/S). Several neutrality statistical tests indicate an excess of rare frequency polymorphisms in the LL-Prochlorococcus data, but an excess of intermediate frequency polymorphisms in the HL-Prochlorococcus data. Distributions of the positively selected sites identified using the likelihood ratio test, when mapped onto the phycoerythrin tertiary structure, reveal that HL- and LL-phycoerythrin should be under different selective patterns. These findings may provide insights into the likely role of selection at the phycoerythrin locus and motivate further research to unveil the function of phycoerythrin in Prochlorococcus.
作为原绿球藻中藻胆蛋白的唯一剩余类型，藻红蛋白的实际作用仍然未知。先前的研究表明，在原绿球藻的两种生态型中发现了两种不同形式的藻红蛋白基因，它们分别特别适应高光（HL）或低光（LL）条件。在这里，我们分析了高光和低光原绿球藻种群中藻红蛋白核苷酸变异的模式。我们的分析显示，与种间比较预期相比，peB和peA中非同义固定替换的数量显著更多。在其他五个与藻红蛋白相关的基因（peZ/V/Y/T/S）中未观察到这种过量的非同义固定替换模式。几个中性统计检验表明，低光原绿球藻数据中存在过量的低频多态性，但高光原绿球藻数据中存在过量的中频多态性。使用似然比检验确定的正选择位点分布，映射到藻红蛋白三级结构上时，表明高光和低光藻红蛋白应处于不同的选择模式。这些发现可能为藻红蛋白位点选择的可能作用提供见解，并推动进一步研究以揭示藻红蛋白在原绿球藻中的功能。
