MAIZE A-CHROMOSOME CENTROMERE-ASSOCIATED TANDEM REPEAT (CENTC) FORMS SEVERAL CLUSTERS ALONG A B CHROMOSOME

¹ Department of Agronomy and Plant Genetics and Plant Molecular Genetics Institute, University of Minnesota, St. Paul, MN 55108 USA

² U.S. Department of Agriculture - Agricultural Research Service and Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108 USA

Genomic DNA segments associated with the centromere of maize chromosome 9 were isolated from a cosmid library and previously characterized. One tandem repeat, CentC, was found in the form of well-defined clusters adjacent to or spanning through the centromeric regions of all maize A-chromosomes in the hybrid Seneca 60. Here we report on analyses of the distribution of the CentC repeats along maize chromosomes in Wilbur's Knobless Flint and in a tropical race Zapalote chico; these two are considered correspondingly as varieties with minimal and maximal proportions of heterochromatin per maize genome. Even though these two varieties have dramatic differences in copy number of 180-bp and 350-bp (TR1) knob-associated tandem repeats, the distribution and proportion of CentC centromere-associated tandem repeats in A-chromosomes of these two varieties are quite similar. However, a B chromosome pair present in Zapalote chico has several (about 10) clusters of CentC repeats. One cluster is located at the essentially terminal centromere region while other clusters are unevenly placed through the distal part of the B chromosome. There is a small cryptic knob region on the B chromosome, which is composed of small clusters of 180-bp and TR1 repeats. These observations raise the question of the function of CentC repeats in maize B and A chromosomes and provide the first data on the presence of a significant amount of a specific class of tandem repeat, CentC, in a maize B chromosome.