Localization and activity of rRNA genes on fenugreek (Trigonella foenum-graecum L.) chromosomes by fluorescent in situ hybridization and silver staining

 Fenugreek (Trigonella foenum-graecum L.), an annual legume crop grown mainly for seed at present, has the potential to be a high-quality forage crop in western Canada. A cytological survey of germplasm stored at the USDA germplasm center demonstrated a somatic karyotype with a chromosome number of 2n=16. Structural details of two pairs of chromosomes (numbers 1 and 2) showed secondary constrictions that were presumed to be the site of rRNA genes. Fluorescent in situ hybridization (FISH) with a heterologous rRNA gene probe from wheat was utilized to physically map their location for the first time on fenugreek chromosomes. Strong hybridization signals of apparently similar copy-number sequences were detected primarily near the centromere on the metacentric chromosome 1 and near the telomere on the acrocentric chromosome 2. Silver staining of the nucleolar organizing region provided evidence that both the sites were transcriptionally active and independently capable of forming a nucleolus. However, the site on chromosome number 2 was relatively more active than the one on chromosome number 1.