RICE (ORYZA-SATIVA) CENTROMERIC REGIONS CONSIST OF COMPLEX DNA

Rice bacterial artificial chromosome clones containing centromeric DNA were isolated by using a DNA sequence (pSau3A9) that is present in th e centromeres of Gramineae species. Seven distinct repetitive DNA elem ents were isolated from a 75-kilobase rice bacterial artificial chromo some clone. All seven DNA elements are present in every rice centromer e as demonstrated by fluorescence in situ hybridization. Six of the el ements are middle repetitive, and their copy numbers range from approx imate to 50 to approximate to 300 in the rice genome. Five of these si x middle repetitive DNA elements are present in all of the Gramineae s pecies, and the other element is detected only in species within the B ambusoideae subfamily of Gramineae, All six middle repetitive DNA elem ents are dispersed in the centromeric regions. The seventh element, th e RCS2 family, is a tandem repeat of a 168-bp sequence that is represe nted approximate to 6,000 times in the rice genome and is detected onl y in Oryza species. Fiber-fluorescence in situ hybridization analysis revealed that the RCS2 family is organized into long uninterrupted arr ays and resembles previously reported tandem repeats located in the ce ntromeres of human and Arabidopsis thaliana chromosomes. We characteri zed a large DNA fragment derived from a plant centromere and demonstra ted that rice centromeres consist of complex DNA, including both highl y and middle repetitive DNA sequences.