GTP Binding Protein EMB2738 And Thioredoxin AtECB1 Regulate The Mechanism Of Chloroplast Development

Chloroplast is a place for photosynthesis,which plays important role in plant growth and development.Chloroplast development needs the coordinated gene expression between the nuclear and the chloroplast genome.Most of nuclear-encoded chloroplast proteins play important roles in maintaining chloroplast function.In this dissertation,the functions of two nuclear-encoded chloroplast-targeted proteins,EMB2738 and AtECB1,in plant growth and development were investigated through genetics,cell biology,molecular biology,and biochemistry.In this study,a chloroplast-localized protein,EMB2738,was reported to be involved in embryogenesis in Arabidopsis.EMB2738 knockout led to defective embryos,and the embryo development in emb2738 was interrupted after the globular stage.Severely impaired chloroplast development was observed in these aborted embryos.Complementation experiments identified the AT3G12080 locus as EMB2738.The expression levels of chloroplast-encoded photosynthetic genes,which are transcribed by plastid-encoded RNA polymerase(PEP),are predominantly decreased in defective embryogenesis,compared with those in the wild-type.Accumulation of these photosynthetic-related proteins in emb2738 embryo are seriously reduced.The results showed that the expression of plastid genes was needed in embryogenesis,and the activity of PEP was affected by EMB2738,a GTP-binding protein.Silencing of the EMB2738 orthologous in tobacco through a virus-induced genome silencing technique resulted in an albinism phenotype,vacuolated chloroplasts and decreased PEPdependent plastid transcription.These results suggested that NbEMB2738 might be involved in plastid gene expression.The expression of NbEMB2738 could rescue the defective embryogenesis of the emb2738 mutant,but the complementary plants still showed albino phenotype.It is speculated that NbEMB2738 could enhance the transcriptional activity of PEP and promote embryonic development,but this activity can not meet the needs of seedling development.These results indicated that the PEP transcriptional activity of EMB2738 plays an important role in embryogenesis and plant growth.In this work,we also further investigated the function of thioredoxin,AtECB1.AtECB1 plays an important role in seed germination and early chloroplast development.Biochemical assay showed that AtECB1 can interact with the core protein of the PEP complex,RpoA,and located mainly in the 356 kDa complex of the thylakoid membrane fractions.Furthermore,Genetic and biochemical analysis showed that AtECB1 interacted with its homologous protein,AtECB1-like.But there are different roles between the proteins.AtECB1 contains four cysteines which play an important role in regulating thioredoxin reductase activity.Nevertheless,the four mutated versions of AtECB1 could complementary the phenotype of atecb1 mutant.In conclusion,the loss of redox at one site of AtECB1 protein was not essential for autotrophic growth under normal condition.These results are contributing to understand the regulation of plastid gene expression by redox.