Balance between Cytosolic and Chloroplast Translation Affects Leaf Variegation

Abstract

The development of functional chloroplasts relies on the fine coordination of expressions of both nuclear and chloroplast genomes. We have been using the Arabidopsis () () leaf variegation mutant as a tool to dissect the regulation of chloroplast development. In this work, we screened for genetic enhancer modifiers termed () mutants and report the characterization of the first locus, We showed that encodes the cytosolic 80S ribosome 40S small subunit protein RPS21B and the loss of causes the enhancement of leaf variegation. We further demonstrated that combined S21 activities from EVR1 and its close homolog, EVR1L1, are essential for Arabidopsis, and they act redundantly in regulating leaf development and leaf variegation. Moreover, using additional cytosolic ribosomal protein mutants, we showed that although mutations in cytosolic ribosomal proteins all enhance leaf variegation to varying degrees, the 40S subunit appears to have a more profound role over the 60S subunit in regulating VAR2-mediated chloroplast development. Comprehensive genetic analyses with suppressors that are defective in chloroplast translation established that the enhancement of leaf variegation by cytosolic ribosomal protein mutants is dependent on chloroplast translation. Based on our data, we propose a model that incorporates the suppression and enhancement of leaf variegation, and hypothesize that VAR2/AtFtsH2 may be intimately involved in the balancing of cytosolic and chloroplast translation programs during chloroplast biogenesis.

A Wheat WRKY Transcription Factor TaWRKY46 Enhances Tolerance to Osmotic Stress in transgenic Arabidopsis Plants

“…The cDNA encoding full-length TaWRKY46 without the stop codon was inserted into the pTF486-GFP vector [54] after it was cloned by PCR using specific primers ( Supplementary Table S2) with BamHI restriction site. Wheat leaf protoplasts were isolated from 10-day-old seedlings according to the method of Shan [55].…”

Disruption of carotene biosynthesis leads to abnormal plastids and variegated leaves in Brassica napus

“…Multiple genetic screens for var2 suppressors in several laboratories have revealed that many suppressors of var2 are genetic factors involved in chloroplast transcription, translation and post-translational turnover. Comprehensive genetic analyses with var2 suppressors defective in chloroplast translation have established that the enhancement of var2 leaf variegation by cytosolic ribosomal protein mutants depends upon chloroplast translation (Wang et al 2018).…”

Genome-wide signatures of plastid-nuclear coevolution point to repeated perturbations of plastid proteostasis systems across angiosperms

“…Recent evidence suggests that changes in cytosolic translation may have strong genetic interactions with plastid proteostasis machinery. Specifically, mutation of a cytosolic ribosome subunit was shown to enhance variegation phenotypes in thylakoid FtsH mutants (Wang et al, 2018). Given that disruption of plastid translation can suppress these same phenotypes (Yu et al, 2008;Liu et al, 2010;Zheng et al, 2016), it appears that ribosomes in both compartments play a key role in maintenance of plastid-nuclear stoichiometric balance.…”