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 insight into the nature of the DNA sequences involved in telomeric regions of Zea luxurians. These new experiments, based on the Southern blotting technique and in situ hybridization, have demonstrated the following: 1) in situ hybridization (FISH) demonstrated the presence of the 180-bp repeat maize-knob-repeat-sequence in DAPI-positive terminal heterochromatic blocks of Z. luxurians (ZL-THB region); 2) Southern blot analysis confirmed that the 180-bp repeat present in maize is also present in Z. diploperennis, Z. luxurians and 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 sited in the ZL-THB region; 4) in situ hybridization (GISH) of probes and blocking-probes with chromosomes of Z. luxurians (using Z. luxurians as a probe and Z. diploperennis or Z. perennis as a blocking-probe) gave strong fluorescence in both cases. Since Z. diploperennis possesses the 180-bp repeat, fluorescence 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 interspersed 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.