The Physical Location of the Gene Ht1 (Helminthosporium Turcium Resistance1) in Maize (Zea Mays L.)

Abstract

A fluorescence in situ hybridization (FISH) procedure was adopted to physically map two RFLP markers, umc22 and umcl22, which are in linkage group 2 in the maize genetic map. The gene ht1 (Helminthosporium turcium resistance 1) is linked closely to umc22 with 4.3 cM on one side and umcl22 with 1.2 cM on the other side. In this study, the FISH results showed the two tested markers were located on both 2L (the long arm of chromosome2) and 7L. The percentage distance from the centromere to the hybridization site was 61.8 for umc22 and 63.0 for umcl22 on 2L, and 47.5 and 48.9 on 7L respectively. It demonstrated that both umc22 and umcl22 had their homologous or homoeologous sequences on 7L besides 2L and they were duplicated sequences. Because genetic and physical maps show the same marker order, the gene ht1 should be physically located between the hybridization sites of umc22 and umcl22 on 2L and probably also should have its homologous or homoeologous sequence between the two hybridization sites on 7L. Actually, the signal spots showing the hybridization sites of the markers umcl22 and umc22 probably also represent the physical location of the ht1, because each signal spot could occupy about 7% of the arm, while the percentage distance between uncl22 and umc22 is only 1.2. The FISH techniques of small low copy DNA sequences for plants are discussed.