Evidence of Genomic Exchanges between Homeologous Chromosomes in a Cross of Peanut with Newly Synthetized Allotetraploid Hybrids
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Citation
Joel Romaric Nguepjop, Hodo-Abalo Tossim, Joseph M. Bell, Jean-Francois Rami, Shivali Sharma, Brigitte Courtois, Nalini Mallikarjuna, Djibril Sane, Daniel Fonceka. (2/11/2016). Evidence of Genomic Exchanges between Homeologous Chromosomes in a Cross of Peanut with Newly Synthetized Allotetraploid Hybrids. Frontiers in Plant Science, 7 (1635), pp. 1-12.
Abstract
Cultivated peanut and synthetics are allotetraploids (2n D 4x D 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.