title: Analysis of the Relationships between DNA Double-Strand Breaks, Synaptonemal Complex and Crossovers Using the Atfas1-4 Mutant.
abstract: Chromatin Assembly Factor 1 (CAF-1) is a histone chaperone that assembles acetylated histones H3/H4 onto newly synthesized DNA, allowing the de novo assembly of nucleosomes during replication. CAF-1 is an evolutionary conserved heterotrimeric protein complex. In Arabidopsis, the three CAF-1 subunits are encoded by FAS1, FAS2 and MSI1. Atfas1-4 mutants have reduced fertility due to a decrease in the number of cells that enter meiosis. Interestingly, the number of DNA double-strand breaks (DSBs), measured by scoring the presence of γH2AX, AtRAD51 and AtDMC1 foci, is higher than in wild-type (WT) plants, and meiotic recombination genes such AtCOM1/SAE2, AtBRCA1, AtRAD51 and AtDMC1 are overexpressed. An increase in DSBs in this mutant does not have a significant effect in the mean chiasma frequency at metaphase I, nor a different number of AtMLH1 nor AtMUS81 foci per cell compared to WT at pachytene. Nevertheless, this mutant does show a higher gene conversion (GC) frequency. To examine how an increase in DSBs influences meiotic recombination and synaptonemal complex (SC) formation, we analyzed double mutants defective for AtFAS1 and different homologous recombination (HR) proteins. Most showed significant increases in both the mean number of synapsis initiation points (SIPs) and the total length of AtZYP1 stretches in comparison with the corresponding single mutants. These experiments also provide new insight into the relationships between the recombinases in Arabidopsis, suggesting a prominent role for AtDMC1 versus AtRAD51 in establishing interhomolog interactions. In Arabidopsis an increase in the number of DSBs does not translate to an increase in the number of crossovers (COs) but instead in a higher GC frequency. We discuss different mechanisms to explain these results including the possible existence of CO homeostasis in plants.
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Varas
authors.affiliation: School of Biosciences, University of Birmingham, Birmingham, United Kingdom.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Sánchez-Morán
authors.affiliation: Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America; Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina, United States of America.
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Copenhaver
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Juan L
authors.initials: JL
authors.lastname: Santos
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad Complutense de Madrid, Madrid, Spain.
authors.forename: Mónica
authors.initials: M
authors.lastname: Pradillo
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics*; D001482:Base Composition / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics; D023902:Chromosome Pairing / Q000235:genetics; D032461:Chromosomes, Plant / Q000235:genetics; D003434:Crossing Over, Genetic / Q000235:genetics*; D053903:DNA Breaks, Double-Stranded; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D008540:Meiosis / Q000235:genetics; D000072260:RNA Splicing Factors; D051135:Rad51 Recombinase / Q000235:genetics; D011938:Rec A Recombinases / Q000235:genetics; D013573:Synaptonemal Complex / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; C518085:At2g20020 protein, Arabidopsis; D018797:Cell Cycle Proteins; D018744:DNA, Plant; C422044:FAS protein, Arabidopsis; D000072260:RNA Splicing Factors; C513034:ATDMC1 protein, Arabidopsis; C495146:ATRAD51 protein, Arabidopsis; D051135:Rad51 Recombinase; D011938:Rec A Recombinases