Fluorescent in situ hybridization of the ribosomal RNA genes (5S and 35S) in the genus Lolium: Lolium canariense, the missing link with Festuca?

Abstract

Two groups of taxa can be distinguished within the genus Lolium L. based on the pollination system, chromosome size, chromosomal location of nrDNA (5S and 35S (18S-5.8S-26S)] and nrDNA phylogeny. The first group includes self-pollinated taxa (L. temulentum, L. persicum and L. remotum), whereas the second group comprises cross-pollinated species (L. perenne, L. multiflorum and L. rigidum). Here we describe that the autogamous species have two 5S sites and four 35S sites in their genome. Two of the 35S sites are present in the chromosomes containing the 5S regions. The allogamous taxa possess two 5S rDNA sites and 6-10 35S sites per genome, depending on the species. Two of these regions (35S) may also be present in the chromosomes bearing 5S sites. Our study also demonstrates that Lolium canariense shows a distinctive pattern. It has two 5S and four 35S sites. In this case, the 35S loci are located in different chromosomes than the 5S. This cytogenetic pattern is consistent with that of Festuca pratensis. Thus, despite being allogamous, Lolium canariense does not entirely fit in either of the groups defined for the genus Lolium. The physical mapping of the nrDNA regions in L. canariense is different, and resembles that of F. pratensis, suggesting that this Macaronesian Lolium could be intermediate between Festuca and Lolium.