The DIF1 gene of Arabidopsis is required for meiotic chromosome segregation and belongs to the REC8/RAD21 cohesin gene family

Cohesins are a group of conserved proteins responsible for cohesion between replicated sister chromatids during mitosis and meiosis and which are impl icated in double-strand break repair and meiotic recombination. We describe here the identification and characterisation of an Arabidopsis gene - DETE RMINATE, INFERTILE1 (DIF1), which is a homolog of the Schizosaccharomyces p ombe REC8/RAD21 cohesin genes, and is essential for meiotic chromosome segr egation. Five independent alleles of the DIF1 gene were isolated by transpo son mutagenesis, and the mutants show complete male and female sterility. P ollen mother cells (PMCs) of dif1 mutants show multiple meiotic defects whi ch are represented by univalent chromosomes and chromosome fragmentation at metaphase I, and acentric fragments and chromatin bridges in meiosis I and II. Consequently, chromosome segregation is strongly affected, resulting i n meiotic products of uneven size, shape and of variable ploidy. The simila rities in phenotype, and the sequence homology between DIF1 and the REC8/RA D21 cohesins suggests that cohesin function is largely conserved between eu karyotes and highlights the essential role cohesins play in plant meiosis.