Bna A02.YTG1,encoding a tetratricopeptide repeat protein,is required for early chloroplast biogenesis in Brassica napus

Chloroplasts are essential for plant growth and development,as they play a key role in photosynthesis.The chloroplast biogenesis process is complex and its regulatory mechanism remains elusive.We characterized a spontaneous Brassica napus(rapeseed)mutant,ytg,that showed a delayed greening phenotype in all green organs and retarded growth.We identified Bna A02.YTG1 encoding a chloroplastlocalized tetratricopeptide repeat protein widely expressed in rapeseed tissues.We speculated that the ytg phenotype was caused by the deletion of Bna A02.YTG1 based on sequence comparison of 4608(with normal green leaves,isolated from the elite Chinese rapeseed cultivar ZS11)and ytg combined with transcriptome data and CRISPR/Cas9 gene editing results.The homologous gene(Bna C02.YTG1)restored the phenotype of the mutant.Bna A02.YTG1 interacted with MORF2,MORF8,and OZ1.RNA editing of the ndh D-2,ndh F-290,pet L-5,and ndh G-50 plastid transcripts was affected in ytg.These findings suggested that Bna A02.YTG1 participates in RNA editing events.We predicted 29 RNA editing sites in the chloroplast of Brassica napus by comparison with the Arabidopsis chloroplast genome.We conclude that Bna A02.YTG1 affects the posttranscriptional regulation of plastid gene expression and suggest that a tetratricopeptide repeat protein is involved in the chloroplast RNA editing in rapeseed.