Chromatin differentiation between Vigna radiata (L.) R. Wilczek and V. unguiculata (L.) Walp. (Fabaceae)

Abstract

A comparative chromosomal evaluation was carried out between Vigna unguiculata (cowpea) and V. radiata (mung bean) with chromomycin A3 (CMA3)/4’,6-diamidino-2-phenylindole (DAPI) banding and fluorescent in situ hybridization (FISH) using 5S/45S ribosomal DNA (rDNA) probes. Both species had symmetric karyotypes (2n = 22), with prevalence of centromeres in chromosomes at median (m) and submedian (sm) regions and chromosomes ranging in size from 2.1 to 1.25 μm (V. unguiculata) and 2.18 to 0.93 μm (V. radiata). Three different banding patterns were identified for V. unguiculata: CMA3+/DAPI0, CMA3++/DAPI–, and CMA3+/DAPI–. The CMA3+/DAPI0 bands were observed in the pericentromeric regions of all chromosomes, while the CMA3++/DAPI– and CMA3+/DAPI– bands were co-localized with the 45S rDNA in the subtelomeric position (chromosomes B, G, and D, J, respectively) and in the proximal position in chromosome F. Two pairs of chromosomes (D and I) bearing interstitial 5S rDNA have been also identified. Vigna radiata displayed CMA30/DAPI+ bands distributed in the centromeric region of chromosomes B, C, and F, while CMA3++/DAPI– bands were co-localized with the 45S rDNA sites in the subtelomeric position of the short arm in the F and K chromosome pairs. Three pairs of 5S rDNA sites were identified, the first in the proximal region of the long arm in chromosome E and the two others in the proximal and subterminal positions in the long arm of chromosome J. These data highlight some divergences regarding the amount and composition of the heterochromatin in both species, allowing the identification of individual chromosomes in V. unguiculata and V. radiata, and a comparison with other members of the Phaseoloid clade.