Ribonucleotide and R-Loop Damage in Plastid DNA and Mitochondrial DNA during Maize Development.

Area of Science:

• Plant molecular biology
• Organelle genetics
• DNA damage and repair

Background:

• Temporary ribonucleotides in DNA are normal, but persistent ones cause DNA damage.
• Organellar genomes (orgDNAs) in maize plastids and mitochondria fragment during leaf development.
• Previous studies identified oxidative and glycation damage in maize orgDNAs.

Purpose of the Study:

• To assess ribonucleotide damage and defense mechanisms in maize organellar DNA during leaf development.
• To investigate the role of ribonucleotide damage in the decline of organellar genome integrity.
• To compare organellar DNA damage in plants grown under light versus dark conditions.

Main Methods:

• Quantification of ribonucleotides and R-loops in organellar DNA throughout maize leaf development.
• Measurement of RNase H protein levels within organelles.
• Comparison of organellar DNA damage markers in leaves grown in light and dark.

Main Results:

• Ribonucleotide damage to maize organellar DNA increased 2- to 5-fold from leaf base to leaf blade.
• This damage was significantly higher in leaves grown under normal light compared to dark conditions.
• Levels of RNase H, a key DNA repair protein, decreased during this developmental transition.

Conclusions:

• Ribonucleotide incorporation represents a significant form of DNA damage in maize organellar genomes.
• Developmental changes and light exposure exacerbate organellar DNA damage.
• Declining RNase H levels, coupled with oxidative and glycation damage, likely contribute to organellar genome fragmentation.