A Bacteriophage-Derived Primase-Helicase Orchestrates Plant Organellar DNA Replication

Area of Science:

• Plant molecular biology
• Organellar DNA replication
• Evolutionary origins of replication machinery

Background:

• Plant organellar DNA replication mechanisms are poorly understood.
• Unlike animal mitochondria, plant organellar replication uses genes with diverse origins (unique, bacterial, bacteriophage).
• The role of bacteriophage-related proteins in plant organellar DNA replication is unclear.

Purpose of the Study:

• To investigate the function of the bacteriophage-related primase-helicase (AtTwinkle) in Arabidopsis thaliana.
• To elucidate the interaction between AtTwinkle and bacterial-related organellar DNA polymerases (AtPolIs).
• To understand the contribution of AtTwinkle to plant organellar DNA replication and genome stability.

Main Methods:

• Analysis of T-DNA insertion mutants of AtTwinkle (ph1 and ph2).
• Phenotypic characterization of mutant lines, including viability and developmental assessment.
• Quantification of organellar DNA copy numbers and assessment of sensitivity to DNA-damaging agents.

Main Results:

• AtTwinkle is essential for double-stranded DNA unwinding in plant organelles.
• AtTwinkle functionally interacts with AtPolIs, coupling DNA unwinding to DNA synthesis.
• Mutants exhibit reduced organellar DNA copy numbers and increased sensitivity to genotoxic agents, indicating impaired DNA repair.

Conclusions:

• AtTwinkle is crucial for plant organellar DNA replication.
• The study reveals a co-evolution of AtTwinkle and AtPolIs from distinct origins to coordinate organellar DNA replication.
• Loss of AtTwinkle function compromises organellar genome integrity and repair pathways.