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QIN Huan, GUO Qingqing, LIU Chenchen, LI Fenglan, ZHANG Hua, CHU Zihan, WANG Jiangxin, LEI Anping. Occurrence and light response of residual plastid genes in a Euglena gracilis bleached mutant strain OflB2[J]. Journal of Oceanology and Limnology, 2020, 38(6): 1858-1866

Occurrence and light response of residual plastid genes in a Euglena gracilis bleached mutant strain OflB2

QIN Huan1, GUO Qingqing1, LIU Chenchen1, LI Fenglan1, ZHANG Hua1, CHU Zihan2, WANG Jiangxin1, LEI Anping1
1 Shenzhen Key Laboratory of Marine Bioresource and Eco-environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen 518000, China;
2 Basis International School SZ, Shenzhen 518000, China
Euglena gracilis is a unicellular green eukaryotic microalga that features characteristics of both plants and animals. The photosynthetic function of its chloroplast is easily lost under stress resulting in bleached mutants, while the physiological role of their residual plastid DNAs remains unclear. In this study, we obtained five bleached mutants by ofloxacin (Ofl) treatment, identified 12 residual plastid genes in five bleached mutants, and determined the mRNA levels in the wild type E. gracilis (WT) and one bleached mutant (OflB2) under dark and light stimulation conditions by quantitative reverse transcribed PCR (qRTPCR). Results show that the expression of all selected plastid genes in both WT and OflB2 mutant did not change significantly in darkness, while their responses to light stimulation were different. Under the light stimulation conditions, half of the genes did not change significantly, while most of the other genes were down-regulated in OflB2 mutant and up-regulated in WT. Therefore, the bleached mutant retains part of the plastid genome and the plastid relic is responsive to light. Our research will help to understand the functions of residual plastid DNA and evolution of chloroplasts.
Key words:    Euglena gracilis|bleached mutant|residual plastid genes|light response   
Received: 2019-06-18   Revised: 2019-09-23
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