Plastid Deficient 1 Is Essential for the Accumulation of Plastid-Encoded RNA Polymerase Core Subunit β and Chloroplast Development in Arabidopsis.

Zhipan Yang,Shunhua Ding,Yi Zhang,Mingxin Liu,Wei Chi,Congming Lu,Huixia Yang,Qingtao Lu,Xiaogang Wen

doi:10.3390/ijms222413648

Abstract

Plastid-encoded RNA polymerase (PEP)-dependent transcription is an essential process for chloroplast development and plant growth. It is a complex event that is regulated by numerous nuclear-encoded proteins. In order to elucidate the complex regulation mechanism of PEP activity, identification and characterization of PEP activity regulation factors are needed. Here, we characterize Plastid Deficient 1 (PD1) as a novel regulator for PEP-dependent gene expression and chloroplast development in Arabidopsis. The PD1 gene encodes a protein that is conserved in photoautotrophic organisms. The Arabidopsis pd1 mutant showed albino and seedling-lethal phenotypes. The plastid development in the pd1 mutant was arrested. The PD1 protein localized in the chloroplasts, and it colocalized with nucleoid protein TRXz. RT-quantitative real-time PCR, northern blot, and run-on analyses indicated that the PEP-dependent transcription in the pd1 mutant was dramatically impaired, whereas the nuclear-encoded RNA polymerase-dependent transcription was up-regulated. The yeast two-hybrid assays and coimmunoprecipitation experiments showed that the PD1 protein interacts with PEP core subunit β (PEP-β), which has been verified to be essential for chloroplast development. The immunoblot analysis indicated that the accumulation of PEP-β was barely detected in the pd1 mutant, whereas the accumulation of the other essential components of the PEP complex, such as core subunits α and β′, were not affected in the pd1 mutant. These observations suggested that the PD1 protein is essential for the accumulation of PEP-β and chloroplast development in Arabidopsis, potentially by direct interaction with PEP-β.

Highlights

Introduction iationsChloroplasts are unique plant organelles that are the site of photosynthesis and some critical metabolic pathways [1,2,3]
Our study provides a new clueMutant for understanding the complex regulating mechanism of Plastid-encoded RNA polymerase (PEP) activity
We further examined ined whether Plastid Deficient 1 (PD1)-GFP was colocalized with red fluorescent protein (RFP) fused with whether PD1-GFP was colocalized with red fluorescent protein (RFP) fused with TRXz, TRXz, a well-characterized protein localized in nucleoids [21]

Summary

Introduction

Introduction iationsChloroplasts are unique plant organelles that are the site of photosynthesis and some critical metabolic pathways [1,2,3]. As a remnant of cyanobacterial endosymbiosis, chloroplasts keep their own genome and gene expression systems. The chloroplast genome of higher plants contains 120~210 thousand base pairs, encoding rRNA, tRNA, and approximately 70~80 protein-encoding genes [5,6]. They are transcribed by nuclear-encoded RNA polymerase (NEP) and/or plastid-encoded RNA polymerase (PEP) [7,8,9]. NEP, a single-subunit polymerase, is responsible for the expression of housekeeping genes, such as RNA polymerase subunit (rpo) genes, as well as several genes involved in gene expression and other essential plastid functions. PEP is a multi-subunit polymerase that is composed of five core subunits (2α, β, β0 , and β00 ) encoded by the plastid rpoA, rpoB, Licensee MDPI, Basel, Switzerland

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