Chloroplast Translation Elongation Factor EF-Tu/SVR11 Is Involved in var2-Mediated Leaf Variegation and Leaf Development in Arabidopsis.

Siyu Liu,Lijun An,Jingxia Shao,Jun Zhao,Jia Guo,Xiayan Liu,Lu Zheng,Fei Yu,Yafei Qi,Jia Jia,Mengdi Zheng

doi:10.3389/fpls.2019.00295

Abstract

Chloroplasts are semiautonomous organelles, retaining their own genomes and gene expression apparatuses but controlled by nucleus genome encoded protein factors during evolution. To analyze the genetic regulatory network of FtsH-mediated chloroplast development in Arabidopsis, a set of suppressor mutants of yellow variegated (var2) have been identified. In this research, we reported the identification of another new var2 suppressor locus, SUPPRESSOR OF VARIEGATION11 (SVR11), which encodes a putative chloroplast-localized prokaryotic type translation elongation factor EF-Tu. SVR11 is likely essential to chloroplast development and plant survival. GUS activity reveals that SVR11 is abundant in the juvenile leaf tissue, lateral roots, and root tips. Interestingly, we found that SVR11 and SVR9 together regulate leaf development, including leaf margin development and cotyledon venation patterns. These findings reinforce the notion that chloroplast translation state triggers retrograde signals regulate not only chloroplast development but also leaf development.

Highlights

Chloroplasts are essential organelles for eukaryotic photosynthetic species, enabling the chemical reactions powered by light energy to reduce CO2 to carbohydrates
We reported the identification of another new var2 suppressor locus, SUPPRESSOR OF VARIEGATION11 (SVR11), which encodes a putative chloroplast-localized prokaryotic type translation elongation factor elongation factor thermo unstable (EF-Tu)
Both 049-002 and svr11-1 showed a virescent phenotype, i.e., a gradual yellow to green leaf color gradient along the leaf proximal-distal axis (Figure 1A). This virescence phenotype was correlated with a reduction of photosynthetic parameters, as indicated by the FV/FM of whole plant chlorophyll fluorescence imaging (Figure 1B). svr11-1 could reverse the leaf variegation of the var2-4 mutant, a stronger allele of var2, indicating that the suppression of var2 leaf variegation by svr11-1 does not depend on the nature of var2 mutation and is not allele specific (Figures 1C,D)

Summary

Introduction

Chloroplasts are essential organelles for eukaryotic photosynthetic species, enabling the chemical reactions powered by light energy to reduce CO2 to carbohydrates. It is believed that chloroplasts evolved from ancient prokaryotic cyanobacteria through endosymbiosis (Martin et al, 2002). This co-evolution process, especially the transfer of most genes of chloroplast progenitors to the host nuclear genomes, have given rise to modern-day chloroplast genomes with only around 120 genes, in contrast to the more than 3,000 genes of the current genome of cyanobacteria, such as Synechocystis sp. The physical separation of nuclear and chloroplast genomes raises at least two important implications. The remaining genes in chloroplast genomes are expressed with prokaryotic gene expression systems, which are regulated by the nuclear genome and must respond to developmental and environmental conditions (Jarvis and López-Juez, 2013)

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