Genetic diversity of 74 T. urartu genotypes was studied using 11 SSR (simple sequence repeats) markers. The number of alleles ranged from 4 to 15, with an average of 8 alleles per primer. The mean values for the expected heterozygosity (He) and polymorphism information content (PIC) over all loci and populations were 0.56 and 0.52, respectively. From a geographic viewpoint the higher diversities were observed in Jordan, followed by Syria and Turkey. Diversity revealed within countries was higher than among them, even in the same regions of the relevant countries. The analysis of molecular variance revealed that most of the genetic variability was accounted for by differences within populations (90%), with less variability among them (10%). The dendrogram generated based on Nei’s dissimilarity matrix revealed three main clusters for which the grouping patterns were not clearly associated with the geographic origins, indicating the gene flow among different countries. Principal coordinate analysis (PCoA) confirmed subgrouping obtained by cluster analysis. In general, genetic distances between geographic regions were low or moderate, which was also supported by low values of pairwise Fst. Our findings can direct the sampling strategies on T. urartu in studied regions to find beneficial alleles. The heterotic groups detected by cluster and PCoA analysis in the present study can serve as effective candidates in crossing programs to broaden the genetic base in T. urartu.
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.
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.
Authors:J. Ahmadi, A. Pour-Aboughadareh, S. Fabriki-Ourang, and A. A. Mehrabi
Glutenin and gliadin subunits play a key role in flour processing quality by network formation in dough. Wild relatives of crops have served as a pool of genetic variation for decades. In this study, 180 accessions from 12 domesticated and wild relatives of wheat were characterized for the glutenin and gliadin genes with allele-specific molecular markers. A total of 24 alleles were detected for the Glu-A3 and Gli-2A loci, which out of 19 amplified products identified as new alleles. Analysis of molecular variance (AMOVA) indicated that 90 and 65% of the genetic diversity were partitioned within two Aegilops and Triticum genera and their species, respectively. Furthermore, all glutenin and gliadin analyzed loci were polymorphic, indicating large genetic diversity within and between the wild species. Our results revealed that allelic variation of Glu-3A and Gli-As.2 is linked to genomic constitutions so that, Ae. caudata (C genome), Ae. neglecta (UM genome), Ae. umbellulata (U genome) and T. urartu (Au genome) harbor wide variation in the studied subunits. Hence, these species can be used in wheat quality breeding programs.
Authors:A. Pour-Aboughadareh, J. Ahmadi, A.A. Mehrabi, A. Etminan, and M. Moghaddam
The knowledge about genetic diversity in the wild relatives of wheat provides useful information for breeding programs and gene pool management. In the present study, an assessment of agro-morphological diversity and molecular variability among 70 accessions of Triticum, belonging to T. boeoticum, T. urartu, T. durum and T. aestivum species, collected from different regions of Iran was made. According to phenotypic analysis, all traits except peduncle length, stem diameter and the number of seeds per spike indicated a high level of diversity among studied accessions. Also, principal component analysis identified six components that explained 87.53% of the total variation in agro-morphological traits. In molecular analysis, 15 start codon targeted (SCoT) polymorphism primers produced 166 bands, out of which, 162 (97.59%) were polymorphic. Analysis of molecular variance (AMOVA) indicated the 63% of the variation resided among populations. The maximum value of polymorphism information content (PIC), the observed (Na) and effective (Ne) number of alleles, Nie’s gene diversity (He) and Shannon’s information index (I) was detected for T. boeoticum than the other species. The SCoT-based tree revealed three different groups corresponding to the genomic constitution in Triticum germplasm, which was in part confirmed by STRUCTURE and principal coordinate (PCoA) analyses. Our results indicated a remarkable level of genetic diversity among studied Iranian Triticum species, especially T. boeoticum, which can be of interest for future breeding and other analyses associated with future studies of the wild relatives of wheat. More importantly, our results revealed that SCoT markers could be used to accurate evaluate genetic diversity and phylogenetic relationships among different Triticum species.
Authors:G.J. Ye, L. Wei, W.J. Chen, B. Zhang, B.L. Liu, and H.G. Zhang
Red coleoptile is an easily observed trait in Triticum aestivum and can provide some protection against stress. Here, TaMYB-A1 or TuMYB-A1, homologous to TaMYB-D1, which controls red coleoptile formation in the common wheat cultivar ‘Gy115’, was isolated from eight T. aestivum and 34 T. urartu cultivars. The genome sequence of TaMYB-A1 was 867 bp with an intron of 93 bp, which was similar to the MYBs regulating anthocyanin biosynthesis in T. aestivum but different from other MYB transcription factors regulating anthocyanin biosynthesis. TaMYB-A1 had an integrated DNA-binding domain of 102 amino acids and a transcriptional domain of 42 amino acids, which was responsible for regulating anthocyanin biosynthesis. TaMYB-A1 was assigned to the same branch as the MYBs regulating anthocyanin biosynthesis in a phylogenetic tree. A transient expression analysis showed that TaMYB-A1 induced ‘Opata’ coleoptile cells to synthesize anthocyanin with the help of ZmR. A non-functional allele of TaMYB-a1 existed in common wheat cultivars containing rc-a1. One single nucleotide was deleted 715 bp after the start codon in TaMYB-a1 compared with TaMYB-A1. The deletion caused a frame shift mutation, destroyed the DNA transcription activator domain, and resulted in TaMYB-a1 losing its ability to regulate anthocyanin biosynthesis in ‘Opata’ coleoptile cells. Those cultivars with functional TaMYB-A1 or TuMYB-A1 have red coleoptiles. The isolation of TaMYB-A1 should aid in understanding the molecular mechanisms of coleoptile traits in T. aestivum.