Hybrid incompatibilities in interspecific crosses between tetraploid wheat and its wild diploid relative Aegilops umbellulata

Abstract

Hybrid abnormalities, severe growth abortion and grass-clump dwarfism, were found in the tetraploid wheat/Aegilops umbellulata hybrids, and the gene expression changes were conserved in the hybrids with those in other wheat synthetic hexaploids. Aegilops umbellulata Zhuk., a diploid goatgrass species with a UU genome, has been utilized as a genetic resource for wheat breeding. Here, we examine the reproductive barriers between tetraploid wheat cultivar Langdon (Ldn) and various Ae. umbellulata accessions by conducting interspecific crossings. Through systematic cross experiments, three types of hybrid incompatibilities were found: seed production failure in crosses, hybrid growth abnormalities and sterility in the ABU hybrids. Hybrid incompatibilities were widely distributed over the entire range of the natural species, and in about 50% of the cross combinations between tetraploid Ldn and Ae. umbellulata accessions, ABU F hybrids showed one of two abnormal growth phenotypes: severe growth abortion (SGA) or grass-clump dwarfism. Expression of the shoot meristem maintenance-related and cell cycle-related genes was markedly repressed in crown tissues of hybrids showing SGA, suggesting dysfunction of mitotic cell division in the shoot apices. The grass-clump dwarf phenotype may be explained by down-regulation of wheat APETALA1-like MADS box genes, which act as flowering promoters, and altered expression in crown tissues of the miR156/SPLs module, which controls tiller number and branching. These gene expression changes in growth abnormalities were well conserved between the Ldn/Ae. umbellulata plants and interspecific hybrids from crosses of Ldn and wheat D-genome progenitor Ae. tauschii.

Effect of the U genome on grain hardness in nascent synthetic hexaploids derived from interspecific hybrids between durum wheat and Aegilops umbellulata

“…The values for nucleotide diversity (π) were 0.0046 for Pina and 0.0086 for Pinb, which were higher than values that we previously reported (π = 0.0036) based on three single-copy genomic sequences, which included a gene controlling flowering time, Ppd-1, an ascorbate peroxidase gene, APX, and a carotenoid biosynthetic cyclase gene, e-LCY (Okada et al, 2017).…”

“…Some triploid F1 hybrids between Ldn and Ae. umbellulata show abnormal growth, such as grass-clump dwarfness and severe growth abortion (Okada et al, 2017).…”

“…The regions amplified by ExTaq polymerase (Takara Bio, Shiga, Japan) were sequenced using a BigDye terminator cycle sequencing kit (Applied Biosystems, Foster City, CA, USA) and an Applied Biosystems 3730xl DNA Analyzer (Applied Biosystems). Multiple sequence alignment and population genetic analyses for estimating within-species diversity were performed according to our previous study (Okada et al, 2017). The nucleotide sequences of Pina and Pinb in Ae.…”

“…Hybrid growth abnormalities are frequently observed in interspecific crosses between tetraploid wheat and Ae. umbellulata, while selfed seeds can be obtained in ABU triploid hybrids from some interspecific cross combinations (Okada et al, 2017). Here, we sequenced the Pina-U1 and Pinb-U1 genes in more than 40 accessions of Ae.…”

Phenotypic effects of the U-genome variation in nascent synthetic hexaploids derived from interspecific crosses between durum wheat and its diploid relative Aegilops umbellulata

“…In about 50% of cross combinations between the tetraploid wheat cultivar Langdon (Ldn) and various Ae. umbellulata accessions, the F 1 hybrids with the ABU genome show one of two types of hybrid growth abnormalities, severe growth abortion (SGA) or grass-clump dwarfism (GCD) [29]. Synthetic wheat hexaploids with the AABBUU genome can be obtained from ABU F 1 hybrids showing normal growth and be used as bridges to introduce useful traits from Ae.…”