Cytoplasmic organelle DNA preferentially inserts into open chromatin

Area of Science:

• Genetics
• Molecular Biology
• Genomics

Background:

• DNA transfer from organelles (chloroplasts and mitochondria) to the nucleus is a known phenomenon in eukaryotes.
• The precise mechanisms facilitating this organelle DNA integration into the nuclear genome remain largely unelucidated.
• Previous studies in Nicotiana tabacum suggested mitochondrial DNA integration occurs through DNA double-strand break repair.

Purpose of the Study:

• To identify and characterize nuclear insertions of chloroplast DNA (nupts) in Oryza sativa subsp. indica.
• To investigate the mechanism of chloroplast DNA integration into the nuclear genome.
• To determine if organelle DNA integration preferentially occurs in specific nuclear chromatin environments.

Main Methods:

• Comparative genomics to identify unique nupts in O. sativa subsp. indica compared to O. sativa subsp. japonica.
• Analysis of public DNase-seq data to assess chromatin accessibility at nupt insertion sites.
• Cross-species comparison using chimpanzee and human genomes to analyze mitochondrial DNA (mtDNA) insertions (numts) and chromatin accessibility via DNase-seq and FIRE-seq data.

Main Results:

• Fourteen unique nupts were identified in Oryza sativa subsp. indica.
• Chloroplast DNA integration into the nucleus was found to occur via nonhomologous end joining (NHEJ).
• Both nupts in rice and numts in primates showed a significant preference for insertion into open chromatin regions.

Conclusions:

• Nonhomologous end joining is a key mechanism for chloroplast DNA integration into the nuclear genome in rice.
• Organelle DNA integration into the nucleus is not random and is influenced by the chromatin landscape, favoring accessible regions.
• These findings provide insights into the dynamics of organelle genome evolution and nuclear-genome interactions.