Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

ORGANIZATION OF RDNA LOCI IN THE ANNUAL SPECIES MEDICAGO TRUNCATULA GAERT

FALISTOCCO E., MORETTI C.

Department of Plant Biology and Agro-environmental Biotechnology, University of Perugia, Borgo XX Giugno 74, Perugia, Italy

egiziaf@unipg.it

Medicago truncatula Gaertn., Leguminosae, rDNA, in situ hybridization

Annual species constitute the most numerous component of the genus Medicago. They are wide spread in the Mediterranean regions where they are assuming increasing importance in agriculture as a source of forage and use as a cover crop.

In recent years great interest has been given to M. truncatula, a diploid with 2n=16, characterized by remarkable variability in several morphological traits and synbiotic activity. Because of these characteristics and its small genome (0.98-1.15 pg), it has been proposed as a model species for genetic studies in legumes, especially alfalfa.

Molecular cytogenetic techniques are an extremely valuable means for investigating the genome structure of the species, however in the genus Medicago their use is still very limited. In M. truncatula, fluorescent in situ hybridization (FISH) has been recently applied to analyze the loci of ribosomal genes in two selected lines. Since such genes showed a different number of loci in the two lines, the present study was undertaken to investigate the variability of the genome organization of this species taking into consideration the distribution of rDNA sites. Simultaneous fluorescent in situ hybridization was performed with pTa71 and pXVI probes to determine the localization of 18S-5.8S-25S and 5S rDNA sequences, respectively. Five natural populations were examined.

The results pointed out that 18S-5.8S-25S ribosomal genes are always clustered in two sites which are localized in correspondence to the regions of the nucleolar organizers. On the contrary, noticeable variation was observed in the distribution of 5S sequences: two populations showed one pair of loci, one population two pairs and two populations three pairs of loci of these sequences.

By means of physically locating 5S genes and other sequences it will be possible to identify each chromosome to provide the bases to link genetic and physical maps.