The Pentratricopeptide Repeat Protein DELAYED GREENING1 Is Involved in the Regulation of Early Chloroplast Development and Chloroplast Gene Expression in Arabidopsis

Wei Chi,Dongyuan Zhang,Jinfang Ma,Jinkui Guo,Congming Lu,Lixin Zhang,Fan Chen

doi:10.1104/pp.108.116194

Abstract

An Arabidopsis (Arabidopsis thaliana) mutant that exhibited a delayed greening phenotype (dg1) was isolated from a population of activation-tagged Arabidopsis lines. Young, inner leaves of dg1 mutants were initially very pale, but gradually greened and mature outer leaves, more than 3 weeks old, appeared similar to those of wild-type plants. Sequence and transcription analyses showed that DG1 encodes a chloroplast protein consisting of eight pentratricopeptide repeat domains and that its expression depends on both light and developmental status. In addition, analysis of the transcript profiles of chloroplast genes revealed that plastid-encoded polymerase-dependent transcript levels were markedly reduced, while nucleus-encoded polymerase-dependent transcript levels were increased, in dg1 mutants. Thus, DG1 is probably involved in the regulation of plastid-encoded polymerase-dependent chloroplast gene expression during early stages of chloroplast development.

Highlights

An Arabidopsis (Arabidopsis thaliana) mutant that exhibited a delayed greening phenotype was isolated from a population of activation-tagged Arabidopsis lines
In null mutants of Arabidopsis (Arabidopsis thaliana) sigma factor 6 (AtSig6), light-dependent chloroplast development has been found to be significantly delayed concomitant with reductions in the accumulation of plastid-encoded polymerases (PEPs)-dependent transcripts, indicating that AtSig6 plays an essential role in the regulation of PEP-dependent gene expression (Ishizaki et al, 2005)
These findings indicate that the regulation of PEP-dependent gene expression is much more complex than previously thought, and the nuclear genes involved in this process remain to be identified

Summary

Introduction

An Arabidopsis (Arabidopsis thaliana) mutant that exhibited a delayed greening phenotype (dg1) was isolated from a population of activation-tagged Arabidopsis lines. DG1 is probably involved in the regulation of plastidencoded polymerase-dependent chloroplast gene expression during early stages of chloroplast development. The development of functional chloroplasts (which is essential for the normal autotrophic growth and development of higher plants) is dependent on the coordinated expression of nuclear and chloroplast genes. There are 466 members in Arabidopsis and 480 in rice (Oryza sativa), but their functions are largely unknown (Small and Peeters, 2000; Lurin et al, 2004). Most of these PPR proteins, predicted to be located in the plastid or mitochondria, play essential roles in the posttranscriptional regulation of organelle gene expression. The DG1 gene encodes a novel PPR protein that is probably involved in the regulation of PEP-dependent transcript accumulation

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Conclusion