The tetratricopeptide repeat-containing protein slow green1 is required for chloroplast development in Arabidopsis

Zhihong Hu,Suiwen Hou,Liping Guan,Yan Huang,Huifang Zhang,Fan Xu,Yaqiong Liu,Pingping Qian

doi:10.1093/jxb/ert463

Abstract

A new gene, SG1, was identified in a slow-greening mutant (sg1) isolated from an ethylmethanesulphonate-mutagenized population of Arabidopsis thaliana. The newly formed leaves of sg1 were initially albino, but gradually became pale green. After 3 weeks, the leaves of the mutant were as green as those of the wild-type plants. Transmission electron microscopic observations revealed that the mutant displayed delayed proplastid to chloroplast transition. The results of map-based cloning showed that SG1 encodes a chloroplast-localized tetratricopeptide repeat-containing protein. Quantitative real-time reverse transcription-PCR data demonstrated the presence of SG1 gene expression in all tissues, particularly young green tissues. The sg1 mutation disrupted the expression levels of several genes associated with chloroplast development, photosynthesis, and chlorophyll biosynthesis. The results of genetic analysis indicated that gun1 and gun4 partially restored the expression patterns of the previously detected chloroplast-associated genes, thereby ameliorating the slow-greening phenotype of sg1. Taken together, the results suggest that the newly identified protein, SG1, is required for chloroplast development in Arabidopsis.

Highlights

The chloroplast is a crucial organelle in higher plants
The young inflorescences and siliques of sg1 were white or pale green, and became green as they matured (Fig. 1B, C). These observations are consistent with a pigment deficiency in sg1, and the levels of chlorophyll a and chlorophyll b were measured at different growth stages of leaf development
The tetratricopeptide repeat (TPR) domain consists of a degenerate, 34 amino acid sequence, which is present in tandem arrays of 3–16 motifs (D’Andrea and Regan, 2003; Whitfield and Mainprize, 2010)

Summary

Introduction

The chloroplast is a crucial organelle in higher plants. It is essential for fixation of CO2 and for biosynthesis of carbon skeletons, fatty acids, pigments, and amino acids from inorganic nitrogen (Staehelin, 2000). The plastid genome of Arabidopsis thaliana encodes ~100 proteins; >2000 proteins are encoded by the nuclear genes that function in the chloroplast (Abdallah et al, 2000; Richly and Leister, 2004; Cui, 2006). Normal plastid development depends on the coordination of nuclear and plastid signals This coordination is accomplished by nuclear signals that regulate the expression of plastid-encoded and nuclear-encoded plastid proteins, and by signals sent from the developing plastids to the nucleus

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Conclusion