A Novel Chloroplast Protein RNA Processing 8 Is Required for the Expression of Chloroplast Genes and Chloroplast Development in Arabidopsis thaliana

Abstract

Chloroplast development involves the coordinated expression of both plastids- and nuclear-encoded genes in higher plants. However, the underlying mechanism still remains largely unknown. In this study, we isolated and characterized an Arabidopsis mutant with an albino lethality phenotype named RNA processing 8 (rp8). Genetic complementation analysis demonstrated that the gene AT4G37920 (RP8) was responsible for the mutated phenotype. The RP8 gene was strongly expressed in photosynthetic tissues at both transcription and translation protein levels. The RP8 protein is localized in the chloroplast and associated with the thylakoid. Disruption of the RP8 gene led to a defect in the accumulation of the rpoA mature transcript, which reduced the level of the RpoA protein, and affected the transcription of PEP-dependent genes. The abundance of the chloroplast rRNA, including 23S, 16S, 4.5S, and 5S rRNA, were reduced in the rp8 mutant, respectively, and the amounts of chloroplast ribosome proteins, such as, PRPS1(uS1c), PRPS5(uS5c), PRPL2 (uL2c), and PRPL4 (uL4c), were substantially decreased in the rp8 mutant, which indicated that knockout of RP8 seriously affected chloroplast translational machinery. Accordingly, the accumulation of photosynthetic proteins was seriously reduced. Taken together, these results indicate that the RP8 protein plays an important regulatory role in the rpoA transcript processing, which is required for the expression of chloroplast genes and chloroplast development in Arabidopsis.

Atyco is a Crucial Factor for Thylakoid Formation and Photosynthesis Regulation in Arabidopsis

“…Our analysis of subcellular location confirmed that YCO is located within the chloroplast (Fig. 3), aligning with the previous studies (Chen et al 2022;Kong et al 2021). Hence, YCO protein was required for thylakoid membrane formation and chloroplast development.…”

“…3 C). Therefore, it appears this protein is localized to the chloroplast in Arabidopsis, which is consistent with previous reports (Chen et al 2022;Kong et al 2021).…”

“…Compared to the wild type, the protein levels of PSI subunits (PsaA, PsaH, and PsaL), PSII subunits (PsbA, PsbD, and PsbS), LHCs (LHCA2 and LHCII), Cytb6/f subunits (PetA and PetB), ATPase subunit (AtpB), and NDH subunit (NdhB) were nearly undetectable in the cotyledons and leaves of the yco mutant (Fig. 7), in agreement with previous studies (Chen et al 2022;Kong et al 2021). However, the accumulation of these proteins in the leaves of the RNAi-20 line was significantly higher compared to the cotyledons, although not reaching the levels observed in the wild type.…”

“…Studies of the sig6 mutant, with its cotyledon-specific pale green phenotype, have shown that phenotypic transformation in cotyledons was accompanied by transient of 4.3 kb atpB/E transcript, due to a promoter switch regulated by NEP and PEP (Schweer et al 2006). Recent research also had pointed out that YCO defect led to a significant reduction in the number of mature rpoA transcripts, suggesting a role in the processing of rpoA polycistron (Kong et al 2021). In the YCO knock-down line, compared with WT, the up-regulation of rpoA transcript was evident in cotyledons, but clearly reduced in true leaves (Fig.…”

“…In the present study, we characterized Bn.YCO orthologous gene in Arabidopsis thaliana, ATYCO, also referred to as RP8 (Kong et al 2021), or CDB1 (Chen et al 2022) in Arabidopsis. RP8 has been implicated in the rpoA transcript processing and chloroplast gene expression, while CDB1's involvement in chloroplast ribosome assembly has been highlighted as crucial for the chloroplast development (Chen et al 2022;Kong et al 2021). However, the precise function and regulatory mechanisms of ATYCO gene are still not fully understood and warrant further investigation.…”