Research On B Chromosomes That From Rice Aneuploid Variation

An awned rice plant was discovered among the progeny of the triploid Zhongxian 3037. Cytological investigation showed that this awned plant was a variation with extra chromosomes. Based on the properties of the extra chromosomes during meiosis -e.g., short stature, darkly staining, instability in chromosome number, and lack of synapsis with A chromosomes– they could be considered to be B chromosomes in rice.In our studies, the structure and comment of the extra chromosome, as well as its origin and behavior in meiosis were indicated by using the technique of chromosome microscopy and fluorescence in situ hybridization (FISH). The main results of our studies are as follows:1. B chromosomes in this study are a type of ring chromosomes without telomere revealed by FISH with telomeric repeats. The rice centromeric satellite repeat, CentO and centromere-specific retrotransposon, CRR were used as probes to hybridized to the B chromosomes. The results showed that B chromosomes only had CRR sequence, which might be a key DNA element for B chromosomes'centromere function based on the result of CENH3 immunostaining as well.2. Some BAC clones were selected as probes based on the phenotype of this awned plant with B chromosomes. The results of BAC-FISH showed that, the distinct signals were constantly detected on both chromosome 4 and B chromosomes when hybridized with probes from chromosome 4. Thereout, we confirm that B chromosomes were from rice chromosome 4. 3. In meiosis, the behavior of pollen mother cells (PMCs) that has different number of B chromosomes was distinguished. In meiotic anaphaseⅠ, the sister chromatid of B chromosome in monosomic condition moved into opposite pole. And those in disomic condition got partnership in meiotic prophaseⅠ, the"chromosome bridge"was discovered in anaphaseⅠafter recombination between the ring chromosomes, which resulted in bigger or smaller B chromosomes in the offsprings.4. In the selfing generation, the number of B chromosomes is different among different plants generated from a same B chromosome plant. This result indicates that the transmission of B chromosomes is abnormal from that of the normal A chromosomes.5. B chromosomes were inclined to be lost during somatic propagation. Within the 12 somatic propagated plants, eight were detected with B chromosomes and four without, which became the diploid plant.