Domain of Unknown Function 143 is required for the functioning of PEP-associated protein DG238 in the chloroplast

Plastid-encoded plastid RNA polymerase (PEP) is essential for chloroplast development and plastid gene expression in Arabidopsis thaliana. However, PEP is a large complex, and many proteins in this complex remain to be identified. We previously reported that Delayed Greening 238 (DG238) interacts with PEP subunit protein FLN1 and may function as a PEP-associated protein and participate in early chloroplast development and PEP-dependent plastid gene expression. DG238 contains Domain of Unknown Function 143 (DUF143), whose function is currently unknown. Here, we found that a deficiency of the DUF143 domain in DG238 affected its localization, which resulted in abnormal interactions with PEP-associated proteins in the chloroplast. Furthermore, DG238 lacking the DUF143 domain or DG238 with only this domain failed to function. Interestingly, the lack of conserved amino acids 193–217 of the DUF143 domain in DG238 also affected its function. In addition to FLN1, DG238 also interacts with other PEP-associated proteins, including FSD2, FSD3, MRL7-L, and MRL7, to regulate plastid gene expression. These results suggest that the DUF143 domain is necessary for the functioning of the PEP-associated protein DG238 in chloroplasts.     

A point mutation in the pentatricopeptide repeat motif of the AtECB2 protein causes delayed chloroplast development

AtECB2 encodes a pentatricopeptide repeat (PPR) protein that regulates the editing of the plastid genes accD and ndhF. The ecb2-1 knockout shows an albino phenotype and is seedling lethal. In this study, we isolated an allelic mutant of the AtECB2 gene, ecb2-2, which showed delayed greening phenotype but could complete their life cycle. In this mutant, the Thr(500) is converted to Ile(500) in the 13(th) PPR motif of the AtECB2 protein. Transmission electron microscopy demonstrated that chloroplast development was delayed in both the cotyledons and leaves of the mutant. An investigation of the chloroplast gene expression profile indicated that PEP (plastid-encoded RNA polymerase) activity in ecb2-2 cotyledons was not obviously affected, whereas it was severely impaired in ecb2-1. This result suggests that the PEP activities cause the different phenotypes of the ecb2-1 and ecb2-2 mutants. The editing efficiency of the three editing sites of accD (C794 and C1568) and ndhF (C290) in the mutant was dynamically altered, which was in agreement with the phenotype. This result indicates that the editing efficiency of accD and ndhF in the ecb2-2 mutant is associated with a delayed greening phenotype. As ecb2-2 can survive and set seeds, this mutant can be used for further investigation of RNA editing and chloroplast development in arabidopsis.     

Chloroplast development in Arabidopsis thaliana requires the nuclear-encoded transcription factor sigma B

Development of plastids into chloroplasts, the organelles of photosynthesis, is triggered by light. However, little is known of the factors involved in the complex coordination of light-induced plastid gene expression, which must be directed by both nuclear and plastid genomes. We have isolated an Arabidopsis mutant, abc1, with impaired chloroplast development, which results in a pale green leaf phenotype. The mutated nuclear gene encodes a sigma factor, SigB, presumably for the eubacterial-like plastid RNA polymerase. Our results provide direct evidence that a nuclear-derived prokaryotic-like SigB protein, plays a critical role in the coordination of the two genomes for chloroplast development.     

Young Seedling Stripe1 encodes a chloroplast nucleoid-associated protein required for chloroplast development in rice seedlings

Planta - Young Seedling Stripe1 (YSS1) was characterized as an important regulator of plastid-encoded plastid RNA polymerase (PEP) activity essential for chloroplast development at rice seedling...