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

Mengmeng Kong,Yanyun Liu,Yixin Lan,Hualing Mi,Qingbo Yu,Zhongnan Yang,Yaozong Wu,Xin Chen,Ziyuan Wang,Wantong Qu,Perveen Shahnaz

doi:10.3389/fpls.2021.700975

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.

Highlights

In higher plants, the chloroplast is a kind of semi-autonomous organelle that originated from a free-living cyanobacterium and has retained a reduced genome during the evolutionary process (Raven and Allen, 2003)
RT-PCR results showed that no transcript of the Ribonucleic acid processing 8 (RP8) gene was detected in the rp8 mutant, while it was present in the wild type (Figure 1C)
Our data demonstrated that the chloroplastlocalized RP8 protein is required for the maturation of the polycistronic rpoA transcript, which is essential for PEP function and chloroplast development

Summary

Introduction

The chloroplast is a kind of semi-autonomous organelle that originated from a free-living cyanobacterium and has retained a reduced genome during the evolutionary process (Raven and Allen, 2003). Chloroplasts as the typical plastids in leaf mesophyll cells develop from protoplastids (Valkov et al, 2009). It is estimated that over 3,000 proteins exist in the chloroplast (Sato et al, 1999; Leister, 2003). Most of the chloroplast proteins are encoded by the nuclear genes and imported from the cytosol (Inaba and Schnell, 2008). Chloroplast development involves the coordinated expression of both plastids- and nuclear-encoded genes (Leister, 2003; Lopez-Juez and Pyke, 2005)

Methods

Results

Conclusion