Chloroplasts are important for plant growth and development.RNA editing in chloroplast converts cytidines (Cs) to uridines (Us) at specific transcript positions and provides a correction mechanism to restore conserved codons or creates start or stop codons.However,the underlined molecular mechanism is not yet fully understood.In the present study,we identified a thermo-sensitive mutant in leaf color 1 (tsl1) and found that TSL1 is allelic to DELAYED GREENING 1 (DG1).The missense mutation ofDG 1 in tsl1 mutant confers a high temperature sensitivity and impaired chloroplast development at an elevated ambient temperature in Arabidopsis.Subsequent analysis showed that chloroplast RNA editing at several sites including accD-1568,ndhD-2,and petL-5 is impaired in tsl1 mutant plants grown at an elevated temperature.DG1 interacts with MORF2 and other proteins such as DYW1 and DYW2 involved in chloroplast RNA editing.In vitro RNA electrophoretic mobility shift assay demonstrated that DG1 binds to RNA targets such as accD,ndhD,and petL.Thus,our results revealed that DG1 is important for maintaining chloroplast mRNA editing in Arabidopsis.