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

SILVESTRI, M C; SAMOLUK SS; ROBLEDO G.; LAVIA, G.; ORTÍZ A.; JOSÉ G. SEIJO

Foz de Iguazu

Conferencia; 21st International Chromosome Conference; 2016

The genus Arachis is a South American genus that includes 82 autogamous and geocarpic species. Most 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 and different genomes. Classical and molecular cytogenetics revealed a large karyotype variability among species and they have also been very important for the infrageneric arrangement of the genus. The objective of this research was to make inferences about the direction of changes in different chromosome markers and DNA content during the evolution of the genus. For this purpose, new and available data about cytogenetic (FISH with 45S and 5S rDNA and heterochromatic markers) and DNA genome size (flow cytometry estimated 2C values) were analyzed in a phylogenetic context based on ITS sequences. This analysis revealed key aspects regarding to the evolutionary history of the genus: 1) there is a general tendency of a genome size (Cx) increase, although independent reductions occurred more than once; 2) reduction of the basic chromosome number (from x=10 to x=9) occurred twice; 3) polyploidization based on x=10 occurred more than once; 4) ?A chromosomes? originated only once; 5) different patterns of DAPI/CMA heterochromatic bands were observed in two (out of three) of the main clades; and 6) the number of 5S rDNA loci is generally one pair (exception are found in different clades), while the number of 45S rDNA is variable (2-5 pairs). Most of the chromosome characters analyzed according to the ITS phylogenetic hypothesis for Arachis genus did not show an unidirectional evolutionary history.