E. K. Khlestkina

Genetic diversity in cultivated plants—loss or stability?

Human activities like urbanisation, the replacement of traditional agriculture systems by modern industrial methods or the introduction of modern high-yielding varieties may pose a danger to the biological diversity. Using microsatellite markers, we analysed samples of cultivated wheat (Triticum aestivum L.) collected over an interval of 40–50 years in four comparable geographical regions of Europe and Asia. No significant differences in both the total number of alleles per locus and in the PIC values were detected when the material collected in the repeated collection missions in all four regions were compared. About two-thirds of the alleles were common to both collection periods, while one-third represented collection mission-specific alleles. These findings demonstrate that an allele flow took place during the adaptation of traditional agriculture to modern systems, whereas the level of genetic diversity was not significantly influenced.

Molecular mapping, phenotypic expression and geographical distribution of genes determining anthocyanin pigmentation of coleoptiles in wheat (Triticum aestivum L.)

Abstract Three major gene loci determining the anthocyanin pigmentation of coleoptiles were mapped on the short arms of chromosomes 7A, 7B and 7D, respectively. All three genes map about 15 to 20 cM distal from the centromere and, therefore, it may be concluded that they are members of a homoeologous series and should be designated Rc-A1, Rc-B1 and Rc-D1, respectively. Further homoeologous loci exist in Triticum durum, Triticum tauschii, and most probably in Secale cereale and Hordeum vulgare. By analyzing a synthetic×cultivated wheat cross (ITMI mapping population) under different environmental conditions it was shown that the expression of the genes determining anthocyanin pigmentation of the coleoptiles varies. One additional locus was detected on chromosome 4BL. Beside the mapping data, results of a screening for red coleoptile color genes in 468 mainly European wheat varieties are presented.

Relationship between homoeologous regulatory and structural genes in allopolyploid genome – A case study in bread wheat

BackgroundThe patterns of expression of homoeologous genes in hexaploid bread wheat have been intensively studied in recent years, but the interaction between structural genes and their homoeologous regulatory genes remained unclear. The question was as to whether, in an allopolyploid, this interaction is genome-specific, or whether regulation cuts across genomes. The aim of the present study was cloning, sequence analysis, mapping and expression analysis of F3H (flavanone 3-hydroxylase – one of the key enzymes in the plant flavonoid biosynthesis pathway) homoeologues in bread wheat and study of the interaction between F3H and their regulatory genes homoeologues – Rc (red coleoptiles).ResultsPCR-based cloning of F3H sequences from hexaploid bread wheat (Triticum aestivum L.), a wild tetraploid wheat (T. timopheevii) and their putative diploid progenitors was employed to localize, physically map and analyse the expression of four distinct bread wheat F3H copies. Three of these form a homoeologous set, mapping to the chromosomes of homoeologous group 2; they are highly similar to one another at the structural and functional levels. However, the fourth copy is less homologous, and was not expressed in anthocyanin pigmented coleoptiles. The presence of dominant alleles at the Rc-1 homoeologous loci, which are responsible for anthocyanin pigmentation in the coleoptile, was correlated with F3H expression in pigmented coleoptiles. Each dominant Rc-1 allele affected the expression of the three F3H homoeologues equally, but the level of F3H expression was dependent on the identity of the dominant Rc-1 allele present. Thus, the homoeologous Rc-1 genes contribute more to functional divergence than do the structural F3H genes.ConclusionThe lack of any genome-specific relationship between F3H-1 and Rc-1 implies an integrative evolutionary process among the three diploid genomes, following the formation of hexaploid wheat. Regulatory genes probably contribute more to the functional divergence between the wheat genomes than do the structural genes themselves. This is in line with the growing consensus which suggests that although heritable morphological traits are determined by the expression of structural genes, it is the regulatory genes which are the prime determinants of allelic identity.

SNP Markers: Methods of Analysis, Ways of Development, and Comparison on an Example of Common Wheat

SNPs (single nucleotide polymorphisms), which belong to the last-generation molecular markers, occur at high frequencies in both animal and plant genomes. The development of SNP markers allows to automatize and enhance tenfolds the effectiveness of genotype analysis. This review summarizes literature data on methods of SNP polymorphism analysis. Various methods of developing SNP markers are considered, taking common wheat Triticum aestivum L. as an example. These markers are compared to other DNA markers, in order to ensure adequate choice of marker type for solving various molecular genetic problems.

Mapping genes controlling anthocyanin pigmentation on the glume and pericarp in tetraploid wheat (Triticum durum L.)

A novel gene, designated Pg (purple glume), controlling anthocyanin pigmentation of the glume was identified and mapped in an F2 population from the durum wheat (Triticum durum) cross TRI 15744/TRI 2719. This gene was close to one of the two complementary dominant genes, controlling anthocyanin pigmentation of the pericarp (gene Pp3) in the centromere region of chromosome 2A; the other Pp gene (Pp1) was mapped on the short arm of chromosome 7B, near gene Pc controlling anthocyanin pigmentation of the culm and co-segregating with Pls (purple leaf sheath) and Plb (purple leaf blade). On the basis of the mapping results, the Pp3, Pc, Pls and Plb genes of T. durum were regarded as allelic to the T. aestivumPp3, Pc-B1, Pls-B1 and Plb-B1 loci. The likely allelism of Pp1 in T. durum and T. aestivum remains in dispute, the present durum Pp gene mapped to the short arm of chromosome 7B, whereas in common wheat it was reportedly located on the long arm.

The adaptive role of flavonoids: Emphasis on cereals

The flavonoid biosynthesis pathway yields a large family of phenolic compounds which are involved in many biological activities including plant defense response to a broad spectrum of abiotic and biotic stress factors. In recent years, a wide range of evidences of relationship between the flavonoid biosynthesis and stress has been accumulated based on genetic, physiological and biochemical studies. In this paper, possible mechanisms of counteraction of flavonoid substances to different stress factors are reviewed, and the evidences for relationship between biosynthesis of flavonoid compounds and response to biotic and abiotic stress are summarized with emphasis on cereals.

Functional diversity at the Rc (red coleoptile) gene in bread wheat

The presence of the allele Rc-A1b on chromosome 7A specified the expression profile of the F3h-1 (encoding flavanone 3-hydroxylase) genes and anthocyanin pigmentation in coleoptiles of Russian bread wheat cultivar ‘Saratovskaya 29’. A quantitative RT-PCR analysis compared the temporal expression profile of F3h-A1, F3h-B1, and F3h-D1 in the coleoptiles of ‘Saratovskaya 29’ and the standard cytogenetic stock ‘Chinese Spring’ (‘Hope’ 7A), both of which carry Rc-A1b. There was no within-genotype variation for expression level of the F3h-1 homoeologues at any of the sampling times, but the expression profiles varied markedly between the two genotypes. This result suggested that there may be functional allelic diversity at Rc-A1, which affects the transcription of the F3h-1 genes in colored coleoptiles. Microsatellite-based genetic mapping was used to locate Rc-A1 along with the new loci Pc-A1 (purple culm), Plb-A1 (purple leaf blade), and Pls-A1 (purple leaf sheath) in a single cluster on the short arm of chromosome 7A.

Clustering anthocyanin pigmentation genes in wheat group 7 chromosomes

Two bread wheat crosses were used to genetically map the genes determining anthocyanin pigmentation of the anther (Pan-D1), culm (Pc-B1 and Pc-D1), leaf sheath (Pls-B1), and leaf blade (Plb-B1, Plb-D1). The genes cluster with Rc-1 (red coleoptile) on chromosome arms 7BS and 7DS. A germplasm panel of 37 wheat cultivars and introgression lines was tested for the presence of anthocyanin pigmentation on various plant organs, and significant correlations were established between pigmentation of the coleoptile and culm, coleoptile and leaf blade, coleoptile and anther, and anther and leaf blade.

The Regulation of Anthocyanin Synthesis in the Wheat Pericarp

Bread wheat producing grain in which the pericarp is purple is considered to be a useful source of dietary anthocyanins. The trait is under the control of the Pp-1 homoealleles (mapping to each of the group 7 chromosomes) and Pp3 (on chromosome 2A). Here, TaMyc1 was identified as a likely candidate for Pp3. The gene encodes a MYC-like transcription factor. In genotypes carrying the dominant Pp3 allele, TaMyc1 was strongly transcribed in the pericarp and, although at a lower level, also in the coleoptile, culm and leaf. The gene was located to chromosome 2A. Three further copies were identified, one mapping to the same chromosome arm as TaMyc1 and the other two mapping to the two other group 2 chromosomes; however none of these extra copies were transcribed in the pericarp. Analysis of the effect of the presence of combinations of Pp3 and Pp-1 genotype on the transcription behavior of TaMyc1 showed that the dominant allele Pp-D1 suppressed the transcription of TaMyc1.

Anthocyanin biosynthesis genes location and expression in wheat-rye hybrids.

Studies into gene expression in a foreign background contribute toward understanding of how genes derived from different species or genera manages to co-exist in a common nucleus, on the one hand, and help to estimate possible effectiveness of wide hybridization for cultivated plant improvement, on the other hand. The aim of this study was to investigate conservation of wheat and rye expression networks, using the anthocyanin biosynthesis pathway (ABP) genes as a model system. We isolated and analyzed ABP genes encoding enzymes acting at different steps of the pathway: chalcone-flavanone isomerase (CHI), flavanone 3-hydroxylase (F3H), anthocyanidin synthase (ANS), and anthocyanidin-3-glucoside rhamnosyltransferase (3RT). The rye ABP genes locations we determined (Chi on chromosome 5RL, F3h on 2RL, Ans on 6RL, 3Rt on 5RL, the regulatory Rc—red coleoptile—gene on 4RL) were in agreement with the rearrangements established between rye and wheat chromosomes. Expression of the ABP structural genes was studied in wheat–rye chromosome addition and substitution lines. F3h activation by the Rc gene was found to be critical for the red coleoptile trait formation. It was shown that the rye regulatory Rc gene can activate the wheat target gene F3h and vice versa wheat Rc induces expression of rye F3h. However, lower level of expression of rye F3h in comparison with that of the two wheat orthologues in the wheat–rye chromosome substitution line 2R(2D) was observed. Thus, although work of the wheat and rye ABP gene systems following the formation of wheat–rye hybrids is finely coordinated, some divergence exists between rye and wheat ABP genes, affecting level of gene expression.