Arabidopsis EMB1990 Encoding a Plastid-Targeted YlmG Protein Is Required for Chloroplast Biogenesis and Embryo Development.

Hongyu Chen,Hengjin Hu,Jie Zhao,Lu Li,Shuqin Li

doi:10.3389/fpls.2018.00181

Abstract

In higher plants, embryo development originated from fertilized egg cell is the first step of the life cycle. The chloroplast participates in many essential metabolic pathways, and its function is highly associated with embryo development. However, the mechanisms and relevant genetic components by which the chloroplast functions in embryogenesis are largely uncharacterized. In this paper, we describe the Arabidopsis EMB1990 gene, encoding a plastid-targeted YlmG protein which is required for chloroplast biogenesis and embryo development. Loss of the EMB1990/YLMG1-1 resulted in albino seeds containing abortive embryos, and the morphological development of homozygous emb1990 embryos was disrupted after the globular stage. Our results showed that EMB1990/YLMG1-1 was expressed in the primordia and adaxial region of cotyledon during embryogenesis, and the encoded protein was targeted to the chloroplast. TEM observation of cellular ultrastructure showed that chloroplast biogenesis was impaired in emb1990 embryo cells. Expression of certain plastid genes was also affected in the loss-of-function mutants, including genes encoding core protein complex subunits located in the thylakoid membrane. Moreover, the tissue-specific genes of embryo development were misexpressed in emb1990 mutant, including genes known to delineate cell fate decisions in the SAM (shoot apical meristem), cotyledon and hypophysis. Taken together, we propose that the nuclear-encoded YLMG1-1 is targeted to the chloroplast and required for normal plastid gene expression. Hence, YLMG1-1 plays a critical role in Arabidopsis embryogenesis through participating in chloroplast biogenesis.

Highlights

The individual life of flowering plant begins with the fertilized egg cell, which gives rise to the mature embryo through a series of programmed cell divisions and differentiations
We found that the mutation of AtYLMG1-1 led to seed abortion, which might due to the failure of chloroplast biogenesis during embryo development, and that several important genes known to delineate cell fate decisions were up-regulated or down-regulated in the emb1990 abortive ovules
The Nuclear-Encoded YLMG-1 Protein Is Targeted to the Chloroplast and Required for Chloroplast Biogenesis

Summary

Introduction

The individual life of flowering plant begins with the fertilized egg cell, which gives rise to the mature embryo through a series of programmed cell divisions and differentiations. In Arabidopsis, embryo development follows a regular and predictable pattern, and this precisely controlled process is regulated by a complicated network of gene expression (Boscá et al, 2011; Luo et al, 2014; Crawford et al, 2015; ten Hove et al, 2015; Ueda et al, 2017). Previous studies predicted that about 1000 genes are required for the Arabidopsis embryogenesis, and a portion of these genes have been identified and characterized as essential through the isolation of embryo-defective (emb) mutants (Meinke et al, 2008; Lloyd and Meinke, 2012). The identification and functional characterization of more essential genes in Arabidopsis can help us develop a deeper understanding of the molecular mechanisms and regulatory networks underlying embryogenesis in eukaryotes. The coordination of chloroplast and nuclear gene expression is integrated through intracellular signaling, and required for chloroplast biogenesis as well as growth and development of higher plants

Methods

Results

Conclusion