Genomic affinities in Arachis section Arachis (Fabaceae): molecular and cytogenetic evidence

Abstract

Section Arachis is the largest of nine sections in the genus Arachis and includes domesticated peanut, A. hypogaea L. Most species are diploids (x = 10) with two tetraploids and a few aneuploids. Three genome types have been recognized in this section (A, B and D), but the genomes are not well characterized and relationships of several newly described species are uncertain. To clarify genomic relationships in section Arachis, cytogenetic information and molecular data from amplified fragment length polymorphism (AFLP) and the trnT-F plastid region were used to provide an additional insight into genome composition and species relationships. Cytogenetic information supports earlier observations on genome types of A. cruziana, A. herzogii, A. kempff-mercadoi and A. kuhlmannii but was inconclusive about the genome composition of A. benensis, A. hoehnei, A. ipaensis, A. palustris, A. praecox and A. williamsii. An AFLP dendrogram resolved species into four major clusters and showed A. hypogaea grouping closely with A. ipaensis and A. williamsii. Sequence data of the trnT-F region provided genome-specific information and showed for the first time that the B and D genomes are more closely related to each other than to the A genome. Integration of information from cytogenetics and biparentally and maternally inherited genomic regions show promise in understanding genome types and relationships in Arachis.

Characterization of the Arachis (Leguminosae) D genome using fluorescence in situ hybridization (FISH) chromosome markers and total genome DNA hybridization

“…However, dot blot hybridization challenges those results, since A. glandulifera DNA showed less genomic affinity with A. batizocoi than with any other species of the B genome group and even than the species included in A genome group. Considering the B genome taxa, the fact that A. glandulifera DNA showed strongest hybridization with A. williamsi followed by A. ipaensis, resembles the results obtained with the analysis of the plastid trnT-L region, in which A. glandulifera clustered in a sister clade to that formed by A. batizocoi and some other B genome species (Tallury et al, 2005). Moreover, in that analysis A. williamsi was joined by a polytomy to the cluster of D genome species, whereas A. ipaensis was included (although with a low bootstrap value) into the base of the clade of the B genome species.…”

“…Molecular markers have shown that A. glandulifera is more distantly related to the A genome species than to the B genome species Tallury et al, 2005). Within the latter group, A. batizocoi appears as the species with higher genome affinity with A. glandulifera.…”

“…On the other hand, the weaker hybridization of A. glandulifera DNA with A. benensis is in accordance with the phylogenetic analysis based on amplified fragment length polymorphism (AFLP) since these species clustered in different clades . The strong hybridization of A. glandulifera DNA with A. trinitensis, A. kuhlmannii and A. kempff-mercadoi, which grouped into the cluster of the A genome entities by AFLP analysis Tallury et al, 2005;Moretzsohn et al, 2004), may reflects an intermediate position of A. glandulifera between the A and B genome clades, as was proposed from the analyses of the plastid trnT-L region (Tallury et al, 2005). Dot blot analysis in plants relies largely on the hybridization of genome repetitive sequences since they are a major component of genomes.…”

“…Different analyses using molecular markers have shown a closer relationship between A. glandulifera and the B genome group of species, particularly with A. batizocoi, and a more distant relationship with the A genome species Tallury et al, 2005). However, analysis of the plastid trnT-L region has shown that A. glandulifera lies in an unresolved polytomy out of the clusters formed by A and B genome species (Tallury et al, 2005).…”

“…However, analysis of the plastid trnT-L region has shown that A. glandulifera lies in an unresolved polytomy out of the clusters formed by A and B genome species (Tallury et al, 2005). Additionally, a simple sequence repeat (SSR) analysis by Moretzsohn et al (2004) showed that A. glandulifera formed a cluster with one 2n = 18 species and with Arachis cruziana.…”