Poster: Comparative Genomics

Abs # 18: Karyotyping and sex chromosomes identification in the dioecious plant Humulus lupulus by in situ hybridization

Presenter:	Danilova, Tatiana V, dani095@cityline.ru
Additional Authors	Weber, Gerd  (B)   Karlov, Gennady  (A)
Affiliations:	(A): Department of Biotechnology, Timiryazev Moscow Agricultural Academy (B): University of Hohenheim

About 90% of angiosperms are hermaphroditic, but 3/4 of dicotyledon and monocotyledon families include species with separate staminate and pistillate flowers (dioecious or monoecious). The small number of dioecious species has heteromorphic sex chromosomes. The structure and origin of plants sex chromosomes and their role in sex determination are poorly understood in spite of the long history of their studies. The molecular genetic and cytogenetic approach could give an improved insight into these studies. Our object was to create the karyotype of hops, Humulus lupulus L. (Cannabiaceae) (2n=2x=20), dioecious with heteromorphic sex chromosomes, which are easily distinguishable at meiotic metaphase 1. The mitotic hop metaphase chromosomes are hardly distinguishable because of their homomorphic structure. Only rough hop karyotype descriptions exist. For hops chromosomes identification we carried out the fluorescent in situ hybridization (FISH) with tandemly organized repetitive sequences (18S-25S rDNA, 5S rDNA) in combination with DAPI banding technique and chromosome measurements. The combination of the methods enabled identification of all mitotic hop chromosomes including sex chromosomes. DNA probes revealed hybridization sites on 3 pairs of autosomes in both male and female mitotic plates. All hops autosomes had telomeric DAPI-positive bands. The shortest chromosome in metaphase plate of male plant without DAPI band was defined as chromosome Y. Middle size metacentric chromosome with interstitial DAPI band on the short arm was detected as X. This study is the first step in understanding the structure and evolution of sex chromosomes in hops.