The genome structure of Arachis hypogaea (Linnaeus, 1753) and an induced Arachis allotetraploid revealed by molecular cytogenetics

Abstract

Peanut, Arachis hypogaea (Linnaeus, 1753) is an allotetraploid cultivated plant with two subgenomes derived from the hybridization between two diploid wild species, A. duranensis (Krapovickas & W. C. Gregory, 1994) and A. ipaensis (Krapovickas & W. C. Gregory, 1994), followed by spontaneous chromosomal duplication. To understand genome changes following polyploidy, the chromosomes of A. hypogaea, IpaDur1, an induced allotetraploid (A. ipaensis × A. duranensis)4x and the diploid progenitor species were cytogenetically compared. The karyotypes of the allotetraploids share the number and general morphology of chromosomes; DAPI+ bands pattern and number of 5S rDNA loci. However, one 5S rDNA locus presents a heteromorphic FISH signal in both allotetraploids, relative to corresponding progenitor. Whilst for A. hypogaea the number of 45S rDNA loci was equivalent to the sum of those present in the diploid species, in IpaDur1, two loci have not been detected. Overall distribution of repetitive DNA sequences was similar in both allotetraploids, although A. hypogaea had additional CMA3+ bands and few slight differences in the LTR-retrotransposons distribution compared to IpaDur1. GISH showed that the chromosomes of both allotetraploids had preferential hybridization to their corresponding diploid genomes. Nevertheless, at least one pair of IpaDur1 chromosomes had a clear mosaic hybridization pattern indicating recombination between the subgenomes, clear evidence that the genome of IpaDur1 shows some instability comparing to the genome of A. hypogaea that shows no mosaic of subgenomes, although both allotetraploids derive from the same progenitor species. For some reasons, the chromosome structure of A. hypogaea is inherently more stable, or, it has been at least, partially stabilized through genetic changes and selection.

Major QTLs for resistance to early and late leaf spot diseases are identified on chromosomes 3 and 5 in peanut (Arachis hypogaea)

“…Cultivated peanut is an allotetraploid (AABB genome) with a genome size of 2.7 Gb (Dhillon et al, 1980;Bertioli et al, 2016;Nascimento et al, 2018). It's inbred nature, recent domestication, perhaps single polyploidization event, and the presence of crossing barriers between the cultivated species lines and its wild diploid relatives contribute to the paucity of genetic polymorphism within this species.…”

Brazilian Kayabi Indian accessions of peanut, Arachis hypogaea (Fabales, Fabaceae): origin, diversity and evolution

“…The Xingu accessions had two pairs of chromosomes displaying CMA 3 + bands, situated on the proximal regions of the chromosomes A10 and B10 ( Figures 3A, B) and representing the sum of CMA 3 + bands observed in A. duranensis and A. ipaënsis (Nascimento et al, 2018). These bands differed from those present in the other tetraploids studied.…”

Characterization of mTERF family in allotetraploid peanut and their expression levels in response to dehydration stress

“…Genome structural variations represent large rearrangements of genomic types including deletion, insertion, inversions, duplications and copy number variations [31]. It was reported that at least one pair of chromosomes of IpaDur1, an induced allotetraploid (A. ipaensis  A. duranensis) 4x , has a clear mosaic hybridization pattern indicating recombination between the subgenomes [7]. According to the homology of sequences, most of mTERFs in allotetraploid peanut were obtained from wild diploid, such as AhmTERF1-7, AhmTERF11, AhmTERF13-15, AhmTERF35-36 and AhmTERF50-51.…”

“…Cultivated peanut (Arachis hypogaea) is an allotetraploid species (AABB genome, 2n ¼ 4x ¼ 40) whose ancestral genomes are probably derived from the Agenome species, A. duranensis (AA genome, 2n ¼ 2x ¼ 20), and the B-genome species, A. ipaensis (BB genome, 2n ¼ 2x ¼ 20) [2][3][4]. The hybridization event between two diploid species most likely resulted in the allotetraploid A. hypogaea [4][5][6][7], which occurred about 11,690 years ago and the domestication of A. hypogaea happened about 4500 years ago [8].…”