Mahelka, V., Kopecký, D., Paštová, L.
BMC EVOLUTIONARY BIOLOGY
11:
127,
2011
Klíčová slova:
Abstrakt:
The wheat tribe Triticeae (Poaceae) is a diverse group of grasses representing a textbook example of
reticulate evolution. Apart from globally important grain crops, there are also wild grasses which are of great
practical value. Allohexaploid intermediate wheatgrass, Thinopyrum intermedium (2n = 6x = 42), possesses many
desirable agronomic traits that make it an invaluable source of genetic material useful in wheat improvement.
Although the identification of its genomic components has been the object of considerable investigation, the
complete genomic constitution and its potential variability are still being unravelled. To identify the genomic
constitution of this allohexaploid, four accessions of intermediate wheatgrass from its native area were analysed by
sequencing of chloroplast trnL-F and partial nuclear GBSSI, and genomic in situ hybridization.
The results confirmed the allopolyploid origin of Thinopyrum intermedium and revealed new aspects in its
genomic composition. Genomic heterogeneity suggests a more complex origin of the species than would be
expected if it originated through allohexaploidy alone. While Pseudoroegneria is the most probable maternal parent
of the accessions analysed, nuclear GBSSI sequences suggested the contribution of distinct lineages corresponding
to the following present-day genera: Pseudoroegneria, Dasypyrum, Taeniatherum, Aegilops and Thinopyrum. Two
subgenomes of the hexaploid have most probably been contributed by Pseudoroegneria and Dasypyrum, but the
identity of the third subgenome remains unresolved satisfactorily. Possibly it is of hybridogenous origin, with
contributions from Thinopyrum and Aegilops. Surprising diversity of GBSSI copies corresponding to a Dasypyrum-like
progenitor indicates either multiple contributions from different sources close to Dasypyrum and maintenance of
divergent copies or the presence of divergent paralogs, or a combination of both. Taeniatherum-like GBSSI copies
are most probably pseudogenic, and the mode of their acquisition by Th. intermedium remains unclear.
Hybridization has played a key role in the evolution of the Triticeae. Transfer of genetic material via
extensive interspecific hybridization and/or introgression could have enriched the species’ gene pools significantly.
We have shown that the genomic heterogeneity of intermediate wheatgrass is higher than has been previously
assumed, which is of particular concern to wheat breeders, who frequently use it as a source of desirable traits in
wheat improvement.
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