Evolution and origin of bread wheat

Abstract

Bread wheat (Triticum aestivum, genome BBAADD) is a young hexaploid species formed only 8500-9000 years ago through hybridization between a domesticated free-threshing tetraploid progenitor, genome BBAA, and Aegilops tauschii, the diploid donor of the D subgenome. Very soon after its formation, it spread globally from its cradle in the fertile crescent into new habitats and climates, to become a staple food of humanity. This extraordinary global expansion was probably enabled by allopolyploidy that accelerated genetic novelty through the acquisition of new traits, new intergenomic interactions, and buffering of mutations, and by the attractiveness of bread wheat’s large, tasty, and nutritious grain with high baking quality. New genome sequences suggest that the elusive donor of the B subgenome is a distinct (unknown or extinct) species rather than a mosaic genome. We discuss the origin of the diploid and tetraploid progenitors of bread wheat and the conflicting genetic and archaeological evidence on where it was formed and which species was its free-threshing tetraploid progenitor. Wheat experienced many environmental changes throughout its evolution, therefore, while it might adapt to current climatic changes, efforts are needed to better use and conserve the vast gene pool of wheat biodiversity on which our food security depends.

36-year study reveals stability of a wild wheat population across microhabitats

“…However, plant density was similar in 1984 and in 2020, suggesting that, so far, this has not occurred. Alternatively, it might be that wild emmer wheat has evolved to be resilient to temperature fluctuations that occurred since its speciation 0.8 MYA ago (Levy and Feldman, 2022) and that recent climate changes have not yet reached critical levels - while local adaptation is very local indeed.…”

“…Wild emmer wheat, a self-pollinating, allotetraploid annual cereal (genome BBAA), is the progenitor of durum wheat ( T. turgidum ssp. durum ) and the maternal donor of the A and B sub-genomes of bread wheat ( T. aestivum , genome BBAADD)(Levy and Feldman, 2022), and any gene from wild emmer wheat can be easily transferred to the background of domesticated wheat. Dense population transects were regularly sampled nine times between 1984 and 2020, and each plant was genotyped by sequencing.…”

Significance of introgression hybridization for extension of genetic variability in recipient genome

“…Currently, a huge amount of evidence has been accumulated regarding the participation of transposons in numerous molecular processes that occur when the stability of the genome is disturbed: during hybridization and polyploidization, which constantly accompany the evolution of plants [61,[67][68][69][70]. The activity of transposons induces structural changes in the genome, causes deletions and duplications, and affects gene expression [67][68][69].…”

Transcriptome-wide analyses of RNA m6A methylation in hexaploid wheat reveal its roles in mRNA translation regulation

“…It has a hexaploidy genome (2n = 6× = 42, AABBDD) consisting of three sub-genomes, which is believed to be a result of two rounds of hybridization speciation, with the latest hybridization event occurring between a domesticated emmer ( T. dicoccum , AABB) and a goatgrass ( Aegilops tauschii , DD) ∼8500 years ago. Due to this short period of speciation of bread wheat, many homeologous genes across the sub-genomes are functionally redundant and mutual complementary ( Peng et al, 2011 ; Levy and Feldman, 2022 ). Many genomic blocks including genes in sub-genomes can be well aligned.…”