RESUMO
The maize B chromosome is a dispensable chromosome and therefore serves as a model system to study centromere function. The B centromere region is estimated to be approximately 9,000 kb in size and contains a 1.4 kb repeat that is specific to this centromere. When maintained as a univalent, the B chromosome occasionally undergoes centric misdivision. Consecutive misdivision analysis of the maize B chromosome centromere has generated a collection of functional centromeres that are greatly reduced in complexity. These small centromeres are often correlated with strongly reduced meiotic transmission. Molecular analyses of the misdivision collection have revealed that the smallest functional maize B centromere is a minimum of 110 kb in size. Considering the collection as a whole, meiotic transmission becomes severely compromised when the estimated centromere size is reduced to a few hundred kilobases.
Assuntos
Centrômero/genética , Cromossomos de Plantas/genética , Zea mays/genética , Segregação de Cromossomos/genética , DNA/química , DNA/genética , Meiose/genética , Modelos Genéticos , Peso Molecular , Fuso Acromático/genéticaAssuntos
MicroRNAs/genética , Desenvolvimento Vegetal , Plantas/genética , RNA de Plantas/genética , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/metabolismo , Padronização Corporal/genética , Regulação da Expressão Gênica no Desenvolvimento , Meristema/crescimento & desenvolvimento , MicroRNAs/biossíntese , Modelos Biológicos , Folhas de Planta/crescimento & desenvolvimento , Plantas/metabolismo , RNA de Plantas/biossíntese , Transdução de Sinais/genéticaRESUMO
Meiotic drive is the subversion of meiosis so that particular genes are preferentially transmitted to the progeny. Meiotic drive generally causes the preferential segregation of small regions of the genome; however, in maize we propose that meiotic drive is responsible for the evolution of large repetitive DNA arrays on all chromosomes. A maize meiotic drive locus found on an uncommon form of chromosome 10 [abnormal 10 (Ab10)] may be largely responsible for the evolution of heterochromatic chromosomal knobs, which can confer meiotic drive potential to every maize chromosome. Simulations were used to illustrate the dynamics of this meiotic drive model and suggest knobs might be deleterious in the absence of Ab10. Chromosomal knob data from maize's wild relatives (Zea mays ssp. parviglumis and mexicana) and phylogenetic comparisons demonstrated that the evolution of knob size, frequency, and chromosomal position agreed with the meiotic drive hypothesis. Knob chromosomal position was incompatible with the hypothesis that knob repetitive DNA is neutral or slightly deleterious to the genome. We also show that environmental factors and transposition may play a role in the evolution of knobs. Because knobs occur at multiple locations on all maize chromosomes, the combined effects of meiotic drive and genetic linkage may have reshaped genetic diversity throughout the maize genome in response to the presence of Ab10. Meiotic drive may be a major force of genome evolution, allowing revolutionary changes in genome structure and diversity over short evolutionary periods.
