The D1 protein of photosystem Ⅱ plays a key role in electron transfer in higher plants and algae. The psbA gene,which encoded Dl protein,was regulated by multiple environmental factors such as light. In order to discover the transcriptional patterns of psbA in the unicellular green alga Chlorella pyrenoidosa under autotrophic and heterotrophic cultivations, the complete coding sequence of psbA gene was cloned and its transcriptional expressions were investigated by real-time PCR method. The cloned psbA gene was 2 595 bp long with a 5'-untranslated region of 676 bp and a 3'-untranslated region of 857 bp. The open reading frame of psbA encoded 353 amino acids, it's a +T percentage content was 58.0% ,and the processing way of mature Dl protein was similar to that of higher plant Sorghum vulgare. Real-time PCR results showed that during the 12 h culture period psbA transcription quantities underwent a rising and then a slow declining process under autotrophic nutrition, while they showed no significant difference under heterotrophic growth. In the process from autotrophy to heterotrophy ,psbA expression quantities rose a little at 2 h and reduced to 0.41-fold 4 h later, then decreased gradually. While in the process of heterotrophy to autotrophy psbA expression increased to 1. 69-fold at 4 h and then maintained at a steady levels. The psbA expression decreased about 40%-59% after different concentration DCMU added in the autotrophic cultivation, but was promoted in the heterotrophic cultivation to a certain degree.%psbA基因是高等植物和藻类中介导光合电子传递D1蛋白的编码基因,该基因受光照等因素的调控.以单细胞绿藻蛋白核小球藻为材料,克隆了psbA全编码序列并用荧光定量PCR的方法研究了自养和异养藻psbA基因转录水平的变化,以揭示不同培养方式下psbA基因表达变化规律.结果克隆到2 595 bp psbA序列,包括676 bp的5′-非翻译区和857 bp的3′非翻译区.该psbA基因开放阅读框编码353个氨基酸,A+T百分含量为58.0％,其成熟的D1蛋白加工方式与高等植物高粱相似.荧光定量结果表明,自养藻在光周期内psbA基因表达量先升高后下降,而异养藻psbA表达变化不明显.从自养转为异养2h时psbA表达量略有升高,4h后下降至转化前的0.41倍并缓慢下降,而从异养转为自养psbA表达量增加,4h时增加至1.69倍,4h后趋于稳定.不同浓度光合抑制剂DCMU降低自养小球藻psbA转录活性至未添加组的40％ ～59％,而不同程度地促进了异养藻psbA的转录表达.
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