Plant Organellar Homologous Recombination Depends on Accessory Factors for Recombinase Activity

Plant organellar HR reconstitution in Arabidopsis shows chloroplast AtRecA1 uniquely executes end-joining recombination on large DNA substrates, unlike bacterial-derived AtRecAs.

• Why it matters: Organellar HR depends on diverse proteins of mixed evolutionary origins, but how these components assemble into a functional repair pathway is unclear.
• What they did: The Arabidopsis organellar HR pathway was reconstructed, testing bacterial-derived recombinases, plant-unique ssDNA-binding proteins (Whirly/OSB), RadA/RecG helicases, and AtRecX inhibition.
• The result: Whirly/OSB proteins enhance AtRecA1 end-joining recombination but are mandatory for AtRecA2 and mitochondrial AtRecA3 activities; RadA resolves AtRecAs intermediates, RecG does not, and AtRecX inhibits AtRecA2 while leaving AtRecA1/AtRecA3 largely insensitive.