Abstract: The D1 protein of photosystem Ⅱ plays a key role in electron transfer in higher plants and algae.The psbA gene,which encoded D1 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,its A+T percentage content was 58.0%,and the processing way of mature D1 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.