Holliday junction resolvases mediate chloroplast nucleoid segregation

Abstract

Holliday junctions, four-stranded DNA structures formed during homologous recombination, are disentangled by resolvases that have been found in prokaryotes and eukaryotes but not in plant organelles. Here, we identify monokaryotic chloroplast 1 (MOC1) as a Holliday junction resolvase in chloroplasts by analyzing a green alga mutant defective in chloroplast nucleoid (DNA-protein complex) segregation. is structurally similar to a bacterial Holliday junction resolvase, resistance to ultraviolet (Ruv) C, and genetically conserved among green plants. Reduced or no expression of in leads to growth defects and aberrant chloroplast nucleoid segregation. In vitro biochemical analysis and high-speed atomic force microscopic analysis revealed that MOC 1 (AtMOC1) binds and cleaves the core of Holliday junctions symmetrically. MOC1 may mediate chloroplast nucleoid segregation in green plants by resolving Holliday junctions.

A Prunus persica genome‐wide RNA‐seq approach uncovers major differences in the transcriptome among chilling injury sensitive and non‐sensitive varieties

“…Genes related to the degradation of damaged proteins from the photosystem II displayed contrasting patterns among NS and SE varieties (Table S8, G2‐G6; Lu ), highlighting different abilities of early and late varieties to keep the plastids homeostasis under control during and after cold storage. In addition, the cold‐induced downregulation of MONOKARYOTIC CHLOROPLAST 1 ( MOC1 ), which mediates chloroplast nucleoid segregation in green plants (Kobayashi et al ), might also have a negative impact on plastids homeostasis in SE late varieties.…”

Chloroplast nucleoids as a transformable network revealed by live imaging with a microfluidic device

“…The fluorescence of HU:YFP was stable throughout the cell cycle. Additionally, the morphological changes to chloroplast nucleoids were clearly visualized during cell/chloroplast divisions, which were almost discernible in the images of SYBR Green I-stained cells 9,10 (Fig. 1).…”

“…An earlier study revealed that MOC1 gene, which is required for the final step of homologous recombination, is conserved from green algae to land plants. Reduced or no expression of MOC1 gene lead to aberrant chloroplast nucleoid aggregation and growth defects in the land plant Arabidopsis thaliana 10 .…”

“…Moreover, the abundance of cpHJR, which is one of the key factors involved in this unfolding process, increases after chloroplasts divide. The cpHJR enzyme also introduces nicks into cpDNA molecules that enable the segregation of HJs, thereby relieving torsional stress 10 . Our data also showed that the dynamic disintegration and reformation of spherical chloroplast nucleoids are precisely coordinated with the timing of cell/chloroplast division (Fig.…”

“…Whereas the mechanisms underlying chromatin remodeling in the nucleus or have been investigated extensively, our understanding on the dynamism of chloroplast nucleoids is still in its infancy 8 . Notably, during chloroplast division, nucleoids appear scattered throughout chloroplasts in green algae 9,10 and land plants 11 , likely to ensure the faithful and equal inheritance of chloroplast DNA molecules by daughter chloroplasts 10 . However, the actual behaviors of chloroplast nucleoids in dividing chloroplasts remain unknown.…”