Two meiotic crossover classes cohabit in Arabidopsis: one is dependent on MER3,whereas the other one is not.
BACKGROUND
Crossovers are essential for the completion of meiosis. Recently, two pathways of crossover formation have been identified on the basis of distinct genetic controls. In one pathway, crossover inhibits the occurrence of another such event in a distance-dependent manner. This phenomenon is known as interference. The second kind of crossover is insensitive to interference. The two pathways function independently in budding yeast. Only interference-insensitive crossovers occur in Schizosaccharomyces pombe. In contrast, only interference-sensitive crossovers occur in Caenorabditis elegans. The situation in mammals and plants remains unclear. Mer3 is one of the genes shown to be required for the formation of interference-sensitive crossovers in Saccharomyces cerevisiae.


RESULTS
To unravel the crossover status in the plant Arabidopsis thaliana, we investigated the role of the A. thaliana MER3 gene through the characterization of a series of allelic mutants. All mer3 mutants showed low levels of fertility and a significant decrease (about 75%) but not a total disappearance of meiotic crossovers, with the number of recombination events initiated in the mutants being similar to that in the wild-type. Genetic analyses showed that the residual crossovers in mer3 mutants did not display interference in one set of adjacent intervals.


CONCLUSIONS
Mutation in MER3 in Arabidopsis appeared to be specific to recombination events resulting in interference-sensitive crossovers. Thus, MER3 function is conserved from yeast to plants and may exist in other metazoans. Arabidopsis therefore has at least two pathways for crossover formation, one giving rise to interference-sensitive crossover and the other to independently distributed crossovers.
Mercier
Raphaël
R
Station de Génétique et d'Amélioration des Plantes, Institut National de la Recherche Agronomique, Versailles, France. rmercier@versailles.inra.fr
Jolivet
Sylvie
S
Vezon
Daniel
D
Huppe
Emelyne
E
Chelysheva
Liudmila
L
Giovanni
Maité
M
Nogué
Fabien
F
Doutriaux
Marie-Pascale
MP
Horlow
Christine
C
Grelon
Mathilde
M
Mézard
Christine
C
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D032461:Chromosomes, Plant / Q000235:genetics*; D003433:Crosses, Genetic; D003434:Crossing Over, Genetic / Q000235:genetics / Q000502:physiology*; D020732:Cytogenetic Analysis; D004265:DNA Helicases / Q000235:genetics / Q000502:physiology; D004252:DNA Mutational Analysis; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D005819:Genetic Markers; D008540:Meiosis / Q000502:physiology*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D029681:Arabidopsis Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D005819:Genetic Markers; D029701:Saccharomyces cerevisiae Proteins; C455499:HFM1 protein, S cerevisiae; D004265:DNA Helicases; C502723:MER3 protein, Arabidopsis