First report of bicolour FISH of Berberis diaphana and B. soulieana reveals interspecific differences and co-localization of (AGGGTTT)(3) and rDNA 5S in B. diaphana

BACKGROUND: Berberis consists of approximately 500 species and is the largest genus in Berberidaceae. Most Berberis species lack cytological data, and bicolour fluorescence in situ hybridization (FISH) has never been performed on Berberis. In this work, a karyotype of Berberis diaphana, an alpine Berberis species obtained from an altitude of 3600 m in Wolong National Nature Reserve, China, was analysed and compared with Berberis soulieana Schneid. via FISH using oligonucleotide telomere probes for (AGGGTTT)(3) and 5S rDNA (41 bp) for the first time. RESULTS: Berberis diaphana belonged to cytotype 2A and had the karyotype formula 2n = 2x = 28 = 26 m + 2 sm (2SAT). The mitotic metaphase chromosome lengths ranged from 1.82 ± 0.04 μm to 2.75 ± 0.00 μm. Clear (AGGGTTT)(3) signals were detected at two telomeres in every chromosome and were co–localized with 5S rDNA at the terminal regions of the long arms in the 6(th) pair of chromosomes. One pair of (AGGGTTT)(3) sites was localized in the satellites of the 7(th) pair of chromosomes, which are the only submetacentric chromosomes in this species. Totally 28 chromosomes with one pair of satellited chromosomes were observed in B. soulieana. This species had four 5S rDNA signals with two weak signals at the end of long arms in the 5(th) pair of chromosomes and another two strong signals detected in the interstitial region close to the end of short arms in the 6(th) pair of chromosomes. Each large signal consisted of two smaller signals with secondary constrictions around them. CONCLUSIONS: FISH physical mapping of B. diaphana suggested that (AGGGTTT)(3) and rDNA 5S co-localize at the 6(th) pair of chromosomes. The density, location and number difference of 5S rDNA loci indicated structural differences among the chromosomes between B. diaphana and B. soulieana. Our results provide information that may contribute to future studies on the physical assembly of the Berberis genome and the evolution of rDNA and telomere FISH patterns in Berberis.