Cytogenetic Analysis of <i>Populus trichocarpa</i> – Ribosomal DNA, Telomere Repeat Sequence, and Marker-selected BACs

The 18S-28S rDNA and 5S rDNA loci in <i>Populus trichocarpa</i> were localized using fluorescent in situ hybridization (FISH). Two 18S-28S rDNA sites and one 5S rDNA site were identified and located at the ends of 3 different chromosomes. FISH signals from the <i>Arabidopsis</i>-type telomere repeat sequence were observed at the distal ends of each chromosome. Six BAC clones selected from 2 linkage groups based on genome sequence assembly (LG-I and LG-VI) were localized on 2 chromosomes, as expected. BACs from LG-I hybridized to the longest chromosome in the complement. All BAC positions were found to be concordant with sequence assembly positions. BAC-FISH will be useful for delineating each of the <i>Populus trichocarpa</i> chromosomes and improving the sequence assembly of this model angiosperm tree species.