Whirly proteins maintain plastid genome stability in Arabidopsis.
Maintenance of genome stability is essential for the accurate propagation of genetic information and cell growth and survival. Organisms have therefore developed efficient strategies to prevent DNA lesions and rearrangements. Much of the information concerning these strategies has been obtained through the study of bacterial and nuclear genomes. Comparatively, little is known about how organelle genomes maintain a stable structure. Here, we report that the plastid-localized Whirly ssDNA-binding proteins are required for plastid genome stability in Arabidopsis. We show that a double KO of the genes AtWhy1 and AtWhy3 leads to the appearance of plants with variegated green/white/yellow leaves, symptomatic of nonfunctional chloroplasts. This variegation is maternally inherited, indicating defects in the plastid genome. Indeed, in all variegated lines examined, reorganized regions of plastid DNA are amplified as circular and/or head-tail concatemers. All amplified regions are delimited by short direct repeats of 10-18 bp, strongly suggesting that these regions result from illegitimate recombination between repeated sequences. This type of recombination occurs frequently in plants lacking both Whirlies, to a lesser extent in single KO plants and rarely in WT individuals. Maize mutants for the ZmWhy1 Whirly protein also show an increase in the frequency of illegitimate recombination. We propose a model where Whirlies contribute to plastid genome stability by protecting against illegitimate repeat-mediated recombination.
Maréchal
Alexandre
A
Department of Biochemistry, Université de Montréal, Station Centre-ville, Montréal, QC, Canada.
Parent
Jean-Sébastien
JS
Véronneau-Lafortune
Félix
F
Joyeux
Alexandre
A
Lang
B Franz
BF
Brisson
Normand
N
D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D018742:DNA, Chloroplast / Q000235:genetics*; D004277:DNA, Single-Stranded / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D005838:Genotype; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D016133:Polymerase Chain Reaction; D011485:Protein Binding; D003313:Zea mays / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
D029681:Arabidopsis Proteins; D018742:DNA, Chloroplast; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D010940:Plant Proteins; C503333:Whirly1 protein, Arabidopsis; C503335:Whirly3 protein, Arabidopsis; D049452:Green Fluorescent Proteins