Distribution and sequence analysis of the centromere-associated repetitiveelement CEN38 of Sorghum bicolor (Poaceae)

Fluorescence in situ hybridization (FISH) of a large-insert genomic clone, BAC 27B2, previously suggested that Sorghum bicolor (2n = 20) has the tetra ploid architecture A(b)A(b)B(b)B(b). Here, we report on BAC 22B2 subclone p CEN38 (1047-bp insert) as related to sorghum and sugarcane. Mitotic FISH of six different subclones of BAC 22B2 showed that pCEN38 produced the strong est specificity to the A(b) subgenome and signal occurred primarily near ce ntromeres. Southern blots of pCEN38 to 21 crop plants revealed a narrow tax onomic distribution. Meiotic metaphase I FISH positioned pCEN38 sequences n ear active centromeres. Pachytene FISH revealed that the distributions are trimodal in several B-b and possibly all sorghum chromosomes. DNA sequencin g revealed that the pCEN38 fragment contains three tandemly repeated dimers (<280 bp) of the same sequence family found in sorghum clone pSau3A10, and that each dimer consists of two divergent monomers (<140 bp). Sequence com parisons revealed homology between the pCEN38 monomers and the SCEN 140 bp tandem repeat family of sugarcane. FISH of pCEN38 yielded signal in centrom ere regions of most but not all sugarcane chromosomes. Results suggest that sugarcane and sorghum share at least one ancestor harboring elements simil ar to pCEN38 and SCEN and that each species had an ancestor in which the re petitive element was weakly present or lacking.