Spontaneous generation of diversity inArachisneopolyploids (Arachis ipaënsis×Arachis duranensis)4x replays the early stages of peanut evolution

Abstract

Polyploidy is considered a driving force in plant evolution and domestication. Although in the genus Arachis, several diploid species were traditionally cultivated for their seeds, only the allotetraploid peanut Arachis hypogaea became the successful, widely spread legume crop. This suggests that polyploidy has given selective advantage for domestication of peanut. Here we study induced allotetraploid (neopolyploid) lineages obtained from crosses between the peanut’s progenitor species, A. ipaënsis and A. duranensis, at earlier and later generations. We observed plant morphology, seed dimensions, and genome structure using cytogenetics (FISH and GISH) and SNP genotyping. The neopolyploid lineages show more variable fertility and seed morphology than their progenitors and cultivated peanut. They also showed sexual and somatic genome instability, evidenced by changes of number of detectable 45S rDNA sites, and extensive homoeologous recombination indicated by mosaic patterns of chromosomes and changes in dosage of SNP alleles derived from the diploid species. Genome instability was not randomly distributed across the genome: the more syntenic chromosomes, the higher homoeologous recombination. Instability levels are higher than observed on peanut lines, therefore it is likely that more unstable lines tend to perish. We conclude that early stages of the origin and domestication of the allotetraploid peanut involved two genetic bottlenecks: the first, common to most allotetraploids, is composed of the rare hybridization and polyploidization events, followed by sexual reproductive isolation from its wild diploid relatives. Here we suggest a second bottleneck: the survival of the only very few lineages that had stronger mechanisms for limiting genomic instability.

Use of wild and exotic germplasm for resistance in peanut

“…However, Simpson and Faries (2001) suggested the possibility of multiple duplication events based on archeological evidence. As more species have been studied, genetic differences have led to new insights into the early stages of peanut evolution and how variability was created (Leal-Bertioli et al, 2021;Suassuna et al, 2020). Other genomes were also suggested (Robledo & Seijo, 2010;Seijo et al, 2004;Stalker, 1991), and many species have been considered as the possible donor species for the cultivated peanut (Milla et al, 2005;Raina & Mukai, 1999;Raina et al, 2001;Smartt et al, 1978a).…”

Photosynthetic Efficiency and Glyco-Metabolism Changes in Artificial Triploid Loquats Contribute to Heterosis Manifestation

“…However, with an increased genome dosage, polyploidization often triggers extensive genomic instabilities, causing genetic variations such as genomic rearrangements (genomic exchange and gene loss) [ 2 , 10 , 11 ]. It was reported that the more closely genomes are related to polyploidy, the more likely it is for them to match homoeologous chromosomes, leading to chromosomal exchanges between the two genomes during meiosis [ 12 ].…”