Karyotype and DNA content patterns of the genus Arachis in a phylogenetic context.

SILVESTRI, M.C.; ORTIZ, A. M.; ROBLEDO, G.; SAMOLUK, S.; SEIJO, J.G.; LAVIA, G.I.

Foz do Iguacu

Conferencia; 21st INTERNATIONAL CHROMOSOME CONFERENCE; 2016

The genus Arachis includes 82 autogamous and geocarpic species distributed within a large region of South America. Most of species are diploids with x=10, four are diploids with x=9, and five are tetraploids with x=10. Based on morphology and cross-compatibility these species were arranged in nine sections. Classical and modern molecular cytogenetics revealed huge karyotypic variability within and among species of different sections, which has been useful to establish the genome constitution of some species. In order to extend the karyotypic characterization to representative species of different sections, and infer the role of chromosome changes in the evolution of genus, the bulk of available cytogenetic data was analyzed in the context of phylogenetic relationships established from analysis of ITS sequences. This analysis revealed: 1) a trend towards the expansion of genome size in relation to the increase of chromosome size, 2) chromosome reductions or duplications occurred more than once in the genus, and in two cases were implicated in the origin of genomes, 3) ?A chromosomes? were originated as a unique event in the history of the genus, 4) the presence of four different patterns of C-DAPI+ heterochromatin distribution common to species of different genome and even sections, with an increase of the amount of heterochromatin in the most derived clades, except for B genome species, 5) the presence of one 5S rDNA locus is uniform in almost all species, but in some lineages the increase of number was related to genome differentiation, 6) a more variable number and distribution of 45S rDNA than of 5S loci, and the numerical variation of 45S rDNA was involved in the speciation of particular groups. In conclusion, unlike other genus, diversification in Arachis has occurred by changes in the repeated fractions of genomes (ribosomal, heterochromatine sequences, and possibly others) and not by major structural rearrangements.