Recently, four novel genes named Pinb-2, with 57–60% sequence similarity with wild-type allele Pinb-D1a coding for grain-hardness related puroindoline B have been shown to occur on homoeologous group 7 chromosomes in bread wheat (Triticum aestivum). In the present report, T. monococcum ssp. monococcum (Am genome) revealed a Pinb-2 gene with a poly-G tract and an in-frame TAG stop codon at the 5′ terminus of the coding DNA sequence. The stop codon was observed in 53 accessions of different geographic origins, suggesting that Pinb-2 in ‘monococcum’ wheat is unlikely to be expressed. By contrast, the coding DNA sequence of Pinb-2 in T. urartu (Au genome) was found to be 99% identical to its counterpart on chromosome 7AL in bread and durum (T. turgidum ssp. durum) wheat. Moreover, a sequence very similar to “urartu” Pinb-2 was found in tetraploid wheat T. timopheevii and hexaploid wheat T. zhukovskyi. This latter species exhibited an additional Pinb-2 pseudogene inherited from T. monococcum. The results are discussed in relation to the lineage of T. zhukovskyi and the potential role of Pin-b2 on kernel texture.
Authors:L. Tyryshkin, M. Gashimov, M. Kolesova, and N. Anphilova
Seedling (juvenile) resistance to 3 foliar diseases was studied in 540 samples of 24
L. species from VIR World Collection. Samples of
T. timopheevii, T. militinae, T. zhukovskyi, T. timococcum
and 4 of
were highly resistant to complex population of leaf rust causal agent. Presence of
clones virulent to samples of
(synthetic hexaploids with genome A
GD) indicates to partial suppression of resistance from species with A
G genome by D genome of
. Two samples of
and one of
were resistant to dark-brown leaf spot blotch. Three samples of
and two of
were classified as resistant after inoculation with mixture of 7
isolates. All 239 samples of 6 species studied were susceptible to common root rot. The causes of differences between our results and that obtained in other studies are discussed.
There is still disagreement among scientists on the exact origin of common wheat (Triticum aestivum ssp. aestivum), one of the most important crops in the world. The first step in the development of the hexaploid aestivum group (ABD) may have been hybridisation between T. urartu (A), as pollinator, and a species related to the Sitopsis section of the Aegilops genus (S) as cytoplasm donor, leading to the creation of the tetraploid species T. turgidum ssp. dicoccoides (AB). The following step may have involved hybridisation between T. turgidum ssp. dicoccon (AB genome, cytoplasm donor), a descendant of T. turgidum ssp. dicoccoides, and Ae. tauschii (D genome, pollinator), resulting in the hexaploid species T. aestivum ssp. spelta (ABD) or some other hulled type. This form may have given rise to naked types, including T. aestivum ssp. aestivum (ABD). The ancestors of the tetraploid T. timopheevii (AG) may have been the diploid T. urartu (A genome, pollinator) and Ae. speltoides (S genome, cytoplasm donor). Species in the timopheevii group developed later than those in the turgidum group, as confirmed by the fact that the G genome is practically identical to the S genome of Ae. speltoides, while the more ancient B genome has undergone divergent evolution. Hybridisation between T. timopheevii (AG, cytoplasm donor) and T. monococcum (A m, pollinator) may have resulted in the species T. zhukovskyi (AGA m). Research into the relationships between the various species is of assistance in compiling the taxonomy of wheat and in avoiding misunderstandings arising from the fact that some species are known by two or more synonymous names.