AOBPreview originally published online on February 15, 2006
Annals of Botany 2006 97(4):541-548; doi:10.1093/aob/mcl017
Characterization and Physical Mapping of Ribosomal RNA Gene Families in Plantago
1 Department of Biotechnology, University of Jammu, Jammu — 180 006, J & K, India and 2 Department of Plant Pathology, Wheat Genetics Resource Center, 4024 Throckmorton Plant Sciences Center, Kansas State University, Manhattan, KS 66506-5502, USA
* For correspondence. E-mail manojkdhar{at}rediffmail.com
Received: 15 August 2004 Returned for revision: 28 October 2004 Accepted: 22 December 2005 Published electronically: 15 February 2006
• Background and Aims The organization of rRNA genes in cultivated Plantago ovata Forsk. and several of its wild allies was analysed to gain insight into the phylogenetic relationships of these species in the genus which includes some 200 species.
• Methods Specific primers were designed to amplify the internal transcribed spacer (ITS1 and ITS2) regions from seven Plantago species and the resulting fragments were cloned and sequenced. Similarly, using specific primers, the 5S rRNA genes from these species were amplified and subsequently cloned. Fluorescence in-situ hybridization (FISH) was used for physical mapping of 5S and 45S ribosomal RNA genes.
• Results The ITS1 region is 19–29 bp longer than the ITS2 in different Plantago species. The 5S rRNA gene-repeating unit varies in length from 289 to 581 bp. Coding regions are highly conserved across species, but the non-transcribed spacers (NTS) do not match any database sequences. The clone from the cultivated species P. ovata was used for physical mapping of these genes by FISH. Four species have one FISH site while three have two FISH sites. In P. lanceolata and P. rhodosperma, the 5S and 45S (18S-5·8S-25S) sites are coupled.
• Conclusions Characterization of 5S and 45S rRNA genes has indicated a possible origin of P. ovata, the only cultivated species of the genus and also the only species with x = 4, from a species belonging to subgenus Psyllium. Based on the studies reported here, P. ovata is closest to P. arenaria, although on the basis of other data the two species have been placed in different subgenera. FISH mapping can be used as an efficient tool to help determine phylogenetic relationships in the genus Plantago and show the interrelationship between P. lanceolata and P. lagopus.
Key words: Plantago, Psyllium, rRNA genes, internal transcribed spacers, FISH mapping, phylogeny