Evolutionary relationships in the genus Zea: analysis of repetitive sequences used as cytological FISH and GISH markers

The present study is a revision of our work on evolutionary cytogenetics of the genus Zea, including several new experiments which give a deeper insig ht into the nature of the DNA sequences involved in telomeric regions of Ze a luxurians. These new experiments, based on the Southern blotting techniqu e and in situ hybridization, have demonstrated the following: 1) in situ hy bridization (FISH) demonstrated the presence of the 180-bp repeat maize-kno b-repeat-sequence in DAPI-positive terminal heterochromatic blocks of Z. lu xurians (ZL-THB region), 2) Southern blot analysis confirmed that the 180-b p repeat present in maize is also present in Z diploperennis, Z luxurians a nd Tripsacum dactyloides, but not in Z. perennis; 3) another sequence with targeted sites for endonucleases, but without recognition sites for the 180 -bp repeat, may be interspersed with the 180-bp repeat in a tandem array si ted in the ZL-THB region; 4) in situ hybridization (GISH) of probes and blo cking-probes with chromosomes of Z. luxurians busing Z luxurians as a probe and Z diploperennis or Z perennis as a blocking-probe) gave strong fluores cence in both cases. Since Z diploperennis possesses the 180-bp repeat, flu orescence on Z luxurians chromosomes was not expected. These results can be explained if the ZL-THB regions are composed not only of 180-bp repeats in terspersed with other sequences, but also of other tandem arrays unique to Z. luxurians, which, according to our GISH results, are probably located at the subterminal position.