Anti-SYN1 monoclonal antibody, clone 20.33

The faithful transmission of chromosomes during mitosis and meiosis requires the establishment and subsequent release of cohesion between replicated chromosomes. Sister chromatid cohesion is mediated, in large part, by the cohesin complex, which consists of four highly conserved proteins: SMC1, SMC3, SCC1/REC8 and SCC3. Mitotic cohesin complexes contain SSC1, whereas meiotic cohesin complexes contain the related REC8 protein. As part of studies to identify and characterize proteins required for meiosis in plants, we previously identified a putative Arabidopsis REC8 homolog, referred to as syn1. Preliminary cytological studies indicated that syn1 plants exhibit defects in meiotic chromosome cohesion and condensation that result in fragmentation of the chromosomes and the formation of polyads. In the experiments presented here we show that SYN1 encodes a protein that localizes to arms of meiotic chromosomes from approximately meiotic interphase to anaphase I. The protein is not detected at the centromeres or after metaphase I. Furthermore, fluorescence in situ hybridization experiments on microsporocytes from syn1 plants demonstrate that the mutation eliminates arm cohesion as early as interphase, whereas centromere cohesion is maintained until approximately anaphase I. These results indicate that although the main role of SYN1 is in chromosome arm cohesion, it is also important for maintaining cohesion at the centromeres during late stages of meiosis I.

Enzyme electrophoresis was used to measure genetic variation within, and divergence among, three generations of recently bred synthetic alfalfa generations (Syn(1), Syn(2), and Syn(3)) originating from a polycross of 12 selected parents and several cultivars. Three isozyme loci, exhibiting tetrasomic inheritance in 10-day seedlings, were detected from five enzymatic systems analyzed by polyacrylamide slab gel electrophoresis for about 100 individuals of each alfalfa population. Very high levels of heterozygosity (ranging from 0.521 to 0.699) were observed within alfalfa populations, using polymorphic loci. The reduction in heterozygosity was about 5% from Syn1 to Syn2 and from Syn2 to Syn3. The last open pollinated generation was found to be in W-H equilibrium as well as Gharayonja, a native ecotype under examination, using chi(2)-test. Application of Wright's F-statistics revealed that the estimated overall inbreeding coefficient, (FIT), of 9.4% was mainly related to inbreeding or double reduction in alfalfa (F(IS)= 8.61%) rather than random genetic drift or population differentiation (F(ST)= 1.6%). Therefore, due to very large intra-population diversity, the breeding program of the synthetic alfalfa did not generate a large variety differentiation. However, the use of seedling allozymic loci can be applied successfully for estimation of the population genetic parameters.