Evidence of Genomic Exchanges between Homeologous Chromosomes in a Cross of Peanut with Newly Synthetized Allotetraploid Hybrids

Abstract

Cultivated peanut and synthetics are allotetraploids (2n = 4x = 40) with two homeologous sets of chromosomes. Meiosis in allotetraploid peanut is generally thought to show diploid-like behavior. However, a recent study pointed out the occurrence of recombination between homeologous chromosomes, especially when synthetic allotetraploids are used, challenging the view of disomic inheritance in peanut. In this study, we investigated the meiotic behavior of allotetraploid peanut using 380 SSR markers and 90 F2 progeny derived from the cross between Arachis hypogaea cv Fleur 11 (AABB) and ISATGR278-18 (AAKK), a synthetic allotetraploid that harbors a K-genome that was reported to pair with the cultivated B-genome during meiosis. Segregation analysis of SSR markers showed 42 codominant SSRs with unexpected null bands among some progeny. Chi-square tests for these loci deviate from the expected 1:2:1 Mendelian ratio under disomic inheritance. A linkage map of 357 codominant loci aligned on 20 linkage groups (LGs) with a total length of 1728 cM, averaging 5.1 cM between markers, was developed. Among the 10 homeologous sets of LGs, one set consisted of markers that all segregated in a polysomic-like pattern, six in a likely disomic pattern and the three remaining in a mixed pattern with disomic and polysomic loci clustered on the same LG. Moreover, we reported a substitution of homeologous chromosomes in some progeny. Our results suggest that the homeologous recombination events occurred between the A and K genomes in the newly synthesized allotetraploid and have been highlighted in the progeny. Homeologous exchanges are rarely observed in tetraploid peanut and have not yet been reported for AAKK and AABB genomes. The implications of these results on peanut breeding are discussed.

Partial preferential chromosome pairing is genotype dependent in tetraploid rose

“…This is not the first reported instance of intra‐chromosomal ‘mixosomy’; in rainbow trout it has been proposed that there may be ‘residual tetrasomy’ (Allendorf and Danzmann, ) leading to variable pairing behaviour along a chromosome, albeit with disomic regions confined to the more central regions. A similar phenomenon has also recently been reported in peanut (Leal‐Bertioli et al ., ; Nguepjop et al ., ). It is possible that the pairing behaviour in cultivated tetraploid Rosa is a consequence of its rather exotic pedigree, similar to an observation on the increased occurrence of mixed segregation patterns in trout populations derived from interspecific hybridisation (Allendorf et al ., ).…”

Segmental allopolyploidy in action: Increasing diversity through polyploid hybridization and homoeologous recombination

“…Whilst there are four genomes segregating (maternal and paternal, A and B genomes), SNP markers are biallelic; they can only detect two alleles (fortunately, for our data, it was possible to distinguish allelic dosage). Furthermore, genetic studies of peanut have generally assumed that genetic behavior was of a classic allotetraploid (A and B genomes not recombining), to further complicate analyses, recent evidence indicates that there is some genetic exchange between subgenomes of Arachis allotetraploids (Bertioli et al., ; Leal‐Bertioli et al., ; Nguepjop et al., ). These genetic exchanges can change genome composition from the expected AABB to conformations that could be described as AAAA or BBBB.…”

“…In these cases, the wild chromosome segments have been reported to substitute the homologous segments from the corresponding subgenome of A. hypogaea , in accordance with the common working assumption of classic diploid‐like allotetraploid genetics in cultivated peanut and induced allotetraploids (the A subgenome only recombines with the A genome, and the B subgenome only recombines with the B). However, there have been recent reports of limited autotetraploid genetic behavior (A and B subgenomes recombine) in progenies of cultivated peanut and induced allotetraploids (Leal‐Bertioli et al., ; Bertioli et al., ; Nguepjop et al., ). Thus, it is likely that this genetic behavior has had a previously overlooked impact on the genome and genetics of cultivated peanut and, therefore, of breeding.…”

The genome sequence of segmental allotetraploid peanut Arachis hypogaea

“…These diploid genomes afforded new insights into peanut genetics. Notably, it was possible to infer that some chromosome ends of A. hypogaea had changed from the expected AABB structure to AAAA or BBBB, implying a particular complexity in peanut genetics 6,[15][16][17][18] .…”