Plant & Animal Genomes XVI Conference

January 12-16, 2008
Town & Country Convention Center
San Diego, CA

The Relation Of Mre11 Protein To Early Recombination Nodules During Meiosis

Leslie Lohmiller¹ , Arnaud De Muyt² , Brittany Howard¹ , Hildo Offenberg³ , Christa Heyting³ , Mathilde Grelon² , Lorinda Anderson¹

¹  Department of Biology and Plant Molecular Biology Program, Colorado State University, FT. Collins, CO 80523

²  Institut Jean-Pierre Bourgin, INRA de Versailles, Station de Génétique et d'Amélioration des Plantes UR-254, Route de Saint-Cyr, 78026 Versailles Cedex, France

³  Molecular Genetics Group, Wageningen University, 6703 BD Wageningen, The Netherlands

Early recombination nodules (ENs) are multi-protein complexes that are thought to be involved in synapsis and recombination, but little is known about how they might accomplish these functions. One approach is to examine the cytological behavior of possible EN components such as Mre11, a conserved protein important for repair of numerous, programmed DNA double-strand breaks (DSBs) that occur early in meiotic prophase. To do this, we used light and electron microscopic (EM) immunolocalization of Mre11 protein in Arabidopsis thaliana and tomato (Solanum lycopersicum). Primary microsporocytes from wild-type Arabidopsis plants had numerous fluorescent Mre11 foci associated with chromosomal axes while those from Atmre11 null plants had no label at all. Two mutants that do not make meiotic DSBs (Atspo11-1 and Atprd1) still had numerous Mre11 foci associated with chromosomal axes. In wild-type tomato, numerous Mre11 foci associated preferentially with chromosomal axes, and Mre11 foci were more common in distal euchromatic than in proximal heterochromatic regions of chromosomes, both of which are consistent with known EN patterns from EM. However, by immuno-EM most Mre11 label was associated with synaptonemal complex components rather than ENs. Only 10% (27/241) of ENs were labeled, but the number and distribution of Mre11-labeled ENs are comparable to crossovers for tomato chromosomes. Immunolocalizations of proteins involved in later aspects of recombination are currently underway to explore the possibility that Mre11-labeled ENs indicate later crossovers. Overall, our results show that morphologically similar ENs may have different protein profiles, which likely reflect underlying molecular events and may provide clues to understanding how recombination is regulated.