Novel cellular factors involved in regulation of BRCA2-driven homologous recombination in Ustilago maydis

Abstract

Maintaining genome integrity is critical for all organisms, requiring efficient DNA repair mechanisms to counteract damage from both internal and external sources. Homologous recombination (HR) is a conserved and accurate pathway for repairing DNA double-strand breaks (DSBs). While yeast uses Rad52 as a central HR mediator, higher eukaryotes, including humans, rely on BRCA2. The phytopathogenic fungus Ustilago maydis possesses a BRCA2 homolog, Brh2, and an HR system strikingly similar to that of humans, making it an excellent model for studying recombination. To uncover novel HR regulators, we conducted a genetic screen for suppressors of hydroxyurea (HU) sensitivity in blm mutants. Blm encodes a RecQ-family helicase, and its loss causes defects in replication-associated repair. The screen identified eight suppressor genes: three known HR factors (rad51, dna2, and mph), paraplegin (nuclear-encoded metalloprotease protein that is a member of the AAA protein family, that is located to the inner mitochondrial membrane) and four novel genes—rec3, zdr1, bls9, and bls2. • Rec3 is a Rad51-family ATPase essential for allelic recombination and meiosis, and shows a strong functional connection with Brh2. • Zdr1 is a C2H2-type zinc finger protein; although its deletion does not overtly affect HR, it contributes to general DNA repair processes. • Bls9 and Bls2 are uncharacterized proteins, but Bls9 is involved in HR between chromosome homologs, while Bls2 shows a slow-growth phenotype. Importantly, deletions of rec3, zdr1, bls2, and paraplegin also suppress HU sensitivity in Δgen1 and Δmus81 mutants, suggesting broader roles in recombination-associated repair. In contrast, bls9 deletion does not rescue HU sensitivity in Δgen1, indicating functional specificity. These newly identified factors expand our understanding of HR regulation and provide insights into the complexity and coordination of DNA repair pathways in eukaryotic cells.Book of abstract: 8th EU-US Conference on endogenous DNA damage and repair, TRONDHEIM, NTNU October 5th—8th | 202