Study On Residual Plastid Genes Of Euglena Gracilis And Its Fading Mutant Strains

Euglena,a new superfood on the market,is a nutrient-rich,green single-celled organism that features the characteristics of both plants and animals.Its model species,Euglena gracilis,is a single-celled green eukaryotic microalga whose functional chloroplasts are easy to lose under stresses and become bleached mutants,while the physiological role of their residual plastid DNAs remains unclear.In the present study,we obtained 5 bleached mutant strains by ofloxacin treatment and identified 12 residual plastid genes,namely rps2,rps3,rps8,rps14,rpl5,rpl14,psbA,psaC,rpl16,petB,rbcL and 5srRNA.Quantitative real time PCR(qRT-PCR)was used to obtain expression level of the 11 plastid residual genes(expect rpl16)in WT and one of the bleached mutant(OflB2),which were grown for 5 days under dark conditions and then remained in the dark or stimulated by light conditions for 0.5 and 3 hours.Results showed that the expression of all selected plastid genes in both WT and OflB2 mutant did no change significantly under dark,while their responses to light stimulation were different.Under the light stimulation conditions,except that about half of the genes did not change significantly,6 genes(rpl5,5srRNA,rps14,rps2,rps8,petB)were down-regulated in OflB2 mutant whereas 4 genes(5srRNA,rps14,rpl14,psbA)were up-regulated and rpl5 gene was down-regulated in WT.The present study indicated that the bleach mutant retains part of the plastid genome and the plastid relic is responsive to light.Our research will help to understand the functions of residential plastid DNA and evolution of the chloroplasts.