Centromere function and nondisjunction are independent components of the maize B chromosome accumulation mechanism.
Supernumerary or B chromosomes are selfish entities that maintain themselves in populations by accumulation mechanisms. The accumulation mechanism of the B chromosome of maize (Zea mays) involves nondisjunction at the second pollen mitosis, placing two copies of the B chromosome into one of the two sperm. The B chromosome long arm must be present in the same nucleus for the centromere to undergo nondisjunction. A centromere, containing all of the normal DNA elements, translocated from the B chromosome to the short arm of chromosome 9 was recently found to be epigenetically silenced for centromeric function. When intact B chromosomes were added to this genotype, thus supplying the long arm, the inactive centromere regained the property of nondisjunction causing the translocation chromosome 9 to be differentially distributed to the two sperm or resulted in chromosome breaks in 9S, occasionally producing new translocations. Translocation of the inactive B centromere to chromosome 7 transferred the nondisjunction property to this chromosome. The results provide insight into the molecular and evolutionary basis of this B chromosome accumulation mechanism by demonstrating that nondisjunction is caused by a process that does not depend on normal centromere function but that the region of the chromosome required for nondisjunction resides in the centromeric region.
Han
Fangpu
F
Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211-7400, USA.
Lamb
Jonathan C
JC
Yu
Weichang
W
Gao
Zhi
Z
Birchler
James A
JA
D002503:Centromere / Q000378:metabolism*; D019457:Chromosome Breakage; D032461:Chromosomes, Plant; D003582:Cytogenetics; D017404:In Situ Hybridization, Fluorescence; D009630:Nondisjunction, Genetic; D011058:Pollen / Q000235:genetics; D003313:Zea mays / Q000033:anatomy & histology / Q000235:genetics*