Submitted to: Proceedings of the National Academy of Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/1998
Publication Date: N/A
Interpretive Summary: Decoding how the genetic material, the DNA, of corn is organized and how this DNA organization relates to cellular functions is a challenging task because of its great complexity. A better understanding of this DNA organization in corn would help researchers modify the DNA to improve the crop. The amount of DNA in a cell of a corn plant is similar to that in a human cell, about 2.5 billion basic chemical units strung together. The DN sequences are further organized into physical structures called chromosomes. Each species has a characteristic number of chromosomes. For corn, that number is 10. During normal cell division the chromosomes duplicate so that each of the two resulting cells receive a copy of each chromosome. On each chromosome there is a region called a centromere where special structures attach to pull one copy of each chromosome into each daughter cell. However, little is known about the DNA of these centromeric regions. We have used some novel genetic materials that we recently developed, oat plants that each have one different chromosome of corn added to their own genetic material, to study the DNA organization of centromeres of individual chromosomes of corn. We found two pieces of DNA that were unique to the centromeric regions of the corn chromosomes. Furthermore, the number of copies of each DNA piece in the centromeres varied among the chromosomes demonstrating that each corn chromosome centromere has a unique DNA organization. The discovery of these chromosome centromere components and their organization helps researchers better understand how the genetic material of corn is organized, and thus how breeders can genetically manipulate corn to produce for the farmer corn that is more productive, stress tolerant, and of higher value composition.
Technical Abstract: A set of oat-maize chromosome addition lines with individual maize (Zea mays L.) chromosomes present in plants with a complete oat (Avena sativa L.) chromosome complement provides a unique opportunity to analyze the organization of centromeric regions of each maize chromosome. A DNA sequence MCS1a, described previously as a maize centromere-associated sequence, was used as a probe to isolate cosmid clones from a genomic library made of DNA purified from a maize chromosome 9 addition line. Analysis of six cosmid clones containing centromeric DNA segments revealed a complex organization. The MCS1a sequence was found to comprise a portion of the long terminal repeats (LTRs) of a novel retrotransposon-like repeated element, termed CentA. Two of the six cosmid clones contained regions composed of a newly identified family of tandem repeats, termed CentC. Copies of CentA and tandem arrays of CentC are interspersed with other repetitive elements, including the previously identified maize retroelements Huck and Prem2. Fluorescence in situ hybridization revealed that CentC and CentA elements are limited to the centromeric region of each maize chromosome. The retroelements Huck and Prem2 are dispersed along all maize chromosomes, although Huck elements are present in an increased concentration around centromeric regions. Significant variation in size of the blocks of CentC and in copy number of CentA elements as well as restriction fragment length variations were detected within the centromeric region of each maize chromosome studied. The different proportions and arrangements of these elements and likely others provides each centromeric region a unique overall structure.