ECD1 functions as an RNA-editing trans-factor of rps14-149 in plastids and is required for early chloroplast development in seedlings.

Tian Jiang,Jing Zhang,Yanjiang Feng,Lixin Zhang,Qi Wang,Liwei Rong,Min Ouyang,Qiulai Song

doi:10.1093/jxb/ery139

Abstract

Chloroplast development is a highly complex process and the regulatory mechanisms have not yet been fully characterized. In this study, we identified Early Chloroplast Development 1 (ECD1), a chloroplast-localized pentatricopeptide repeat protein (PPR) belonging to the PLS subfamily. Inactivation of ECD1 in Arabidopsis led to embryo lethality, and abnormal embryogenesis occurred in ecd1/+ heterozygous plants. A decrease in ECD1 expression induced by RNAi resulted in seedlings with albino cotyledons but normal true leaves. The aberrant morphology and under-developed thylakoid membrane system in cotyledons of RNAi seedlings suggests a role of ECD1 specifically in chloroplast development in seedlings. In cotyledons of ECD1-RNAi plants, RNA-editing of rps14-149 (encoding ribosomal protein S14) was seriously impaired. In addition, dramatically decreased plastid-encoded RNA polymerase-dependent gene expression and abnormal chloroplast rRNA processing were also observed. Taken together, our results indicate that ECD1 is indispensable for chloroplast development at the seedling stage in Arabidopsis.

Highlights

Chloroplasts are the exclusive organelles that perform photosynthesis but they are responsible for many other biosynthetic processes, such as the synthesis of amino acids, hormones, and metabolites (Sakamoto et al, 2008).The development of functional chloroplasts is a prerequisite for photosynthesis and is tightly co-ordinated with plant growth and development
GUS staining was observed exclusively in green tissues, such as sepals, stamens, and carpels, but not in petals.Taken together, these findings showed that Early Chloroplast Development 1 (ECD1) was widely expressed throughout the plant, but the highest expression was in the cotyledons, which was consistent with the albino cotyledon phenotype of the ECD1-RNAi transgenic plants
Chloroplast development is closely related to embryo development and, as a consequence, eliminating biosynthetic functions within the chloroplast and interfering with expression of the chloroplast genome often results in embryo lethality in Arabidopsis (Bryant et al, 2011)

Summary

Introduction

Chloroplasts are the exclusive organelles that perform photosynthesis but they are responsible for many other biosynthetic processes, such as the synthesis of amino acids, hormones, and metabolites (Sakamoto et al, 2008).The development of functional chloroplasts is a prerequisite for photosynthesis and is tightly co-ordinated with plant growth and development. Chloroplast gene expression is crucial for chloroplast development, and is carried out by two kinds of RNA polymerases: plastid-encoded bacterial-type RNA polymerase (PEP) and nuclear-encoded phage-type RNA polymerase (NEP) (Hedtke et al, 1997; Liere and Maliga, 2001; Börner et al, 2015). Given their increasing activity during chloroplast development, PEPs are clearly crucial for chloroplast development at early stages of plant growth (Mullet, 1993). Pentatricopeptide repeat (PPR) proteins, which constitute one of the largest protein family in land plants, have been demonstrated to play important roles in chloroplast gene expression and function. Based on the presence of different C-terminal motifs, the PLS subfamily is further divided into the PLS, E, E+, and DYW subgroups (Schmitz-Linneweber and Small, 2008)

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Conclusion