Ribosomal DNA repeat unit polymorphism in 25 Hordeum species

Area of Science:

• Genetics
• Molecular Biology
• Plant Science

Background:

• Ribosomal DNA (rDNA) sequences are crucial for cellular function and exhibit variation across species.
• Understanding rDNA organization provides insights into genome evolution and phylogenetic relationships.

Purpose of the Study:

• To investigate the diversity of tandemly repeated ribosomal DNA (rDNA) sequences in 25 Hordeum species.
• To characterize rDNA repeat unit lengths, organization, and restriction site variations.
• To infer phylogenetic relationships within the Hordeum genus based on rDNA analysis.

Main Methods:

• Utilized the wheat rDNA probe pTA71 for Southern blot analysis of 25 Hordeum species.
• Determined rDNA repeat unit lengths and analyzed restriction fragment patterns (EcoRI, SacI, BamHI, HindIII).
• Correlated rDNA length classes with nucleolar organizing regions (NORs) and mapped restriction sites.

Main Results:

• rDNA repeat unit lengths varied from 8.5 to 10.7 kb, with 1-3 length classes per species generally matching NOR numbers.
• Intraspecific variation in rDNA was observed in H. parodii, H. spontaneum, and H. leporinum.
• Restriction analysis revealed conserved rRNA gene sites but variation in intergenic spacers; five distinct BamHI restriction maps were identified, grouping Hordeum species and suggesting closer relationships for H. bulbosum with certain species.

Conclusions:

• rDNA repeat unit length variation in Hordeum is primarily driven by changes in the intergenic spacer region.
• BamHI restriction site mapping provides a valuable tool for understanding phylogenetic relationships within the Hordeum genus.
• The study highlights the utility of rDNA analysis for elucidating evolutionary patterns in plants.