Haploid meiosis in Arabidopsis: double-strand breaks are formed and repaired but without synapsis and crossovers.
Two hallmark features of meiosis are i) the formation of crossovers (COs) between homologs and ii) the production of genetically-unique haploid spores that will fuse to restore the somatic ploidy level upon fertilization. In this study we analysed meiosis in haploid Arabidopsis thaliana plants and a range of haploid mutants to understand how meiosis progresses without a homolog. Extremely low chiasma frequency and very limited synapsis occurred in wild-type haploids. The resulting univalents segregated in two uneven groups at the first division, and sister chromatids segregated to opposite poles at the second division, leading to the production of unbalanced spores. DNA double-strand breaks that initiate meiotic recombination were formed, but in half the number compared to diploid meiosis. They were repaired in a RAD51- and REC8-dependent manner, but independently of DMC1, presumably using the sister chromatid as a template. Additionally, turning meiosis into mitosis (MiMe genotype) in haploids resulted in the production of balanced haploid gametes and restoration of fertility. The variability of the effect on meiosis of the absence of homologous chromosomes in different organisms is then discussed.
INRA, UMR1318, Institut Jean-Pierre Bourgin, Versailles, France.
Marta
M
Cifuentes
Maud
M
Rivard
Lucie
L
Pereira
Liudmila
L
Chelysheva
Raphael
R
Mercier
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D023902:Chromosome Pairing / Q000235:genetics; D003434:Crossing Over, Genetic / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000235:genetics*; D004171:Diploidy; D005298:Fertility / Q000235:genetics; D006238:Haploidy; D007211:Indoles / Q000737:chemistry; D008540:Meiosis / Q000235:genetics*; D008938:Mitosis / Q000235:genetics; D000070957:MutL Protein Homolog 1; D009154:Mutation; D011058:Pollen / Q000235:genetics / Q000378:metabolism; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D013194:Staining and Labeling / Q000379:methods
D029681:Arabidopsis Proteins; D018797:Cell Cycle Proteins; D007211:Indoles; C507256:REC8 protein, Arabidopsis; C007293:DAPI; C513034:ATDMC1 protein, Arabidopsis; C495146:ATRAD51 protein, Arabidopsis; D051135:Rad51 Recombinase; D011938:Rec A Recombinases; D000251:Adenosine Triphosphatases; C524390:MLH1 protein, Arabidopsis; D000070957:MutL Protein Homolog 1