The General Transcription Repressor TaDr1 Is Co-expressed With TaVrn1 and TaFT1 in Bread Wheat Under Drought

Abstract

The general transcription repressor, TaDr1 gene, was identified during screening of a wheat SNP database using the Amplifluor-like SNP marker KATU-W62. Together with two genes described earlier, TaDr1A and TaDr1B, they represent a set of three homeologous genes in the wheat genome. Under drought, the total expression profiles of all three genes varied between different bread wheat cultivars. Plants of four high-yielding cultivars exposed to drought showed a 2.0-2.4-fold increase in TaDr1 expression compared to controls. Less strong, but significant 1.3-1.8-fold up-regulation of the TaDr1 transcript levels was observed in four low-yielding cultivars. TaVrn1 and TaFT1, which controls the transition to flowering, revealed similar profiles of expression as TaDr1. Expression levels of all three genes were in good correlation with grain yields of evaluated cultivars growing in the field under water-limited conditions. The results could indicate the involvement of all three genes in the same regulatory pathway, where the general transcription repressor TaDr1 may control expression of TaVrn1 and TaFT1 and, consequently, flowering time. The strength of these genes expression can lead to phenological changes that affect plant productivity and hence explain differences in the adaptation of the examined wheat cultivars to the dry environment of Northern and Central Kazakhstan. The Amplifluor-like SNP marker KATU-W62 used in this work can be applied to the identification of wheat cultivars differing in alleles at the TaDr1 locus and in screening hybrids.

Keywords: Amplifluor-like SNP marker; TaDr1; TaFT1; TaVrn1; bioinformatics; drought; general repressor of transcription.

Figure 1

Allele discrimination in eight wheat cultivars (A) and in the segregating population 18-6 (B) using the Amplifluor-like SNP marker KATU-W62. X- and Y-axes show relative amplification units, ΔR_n, for FAM and VIC fluorescence signals, respectively. Red dots represent homozygote (aa) genotypes with allele 1 (FAM) associated with the high yielding cultivars, blue dots represent homozygote (bb) genotypes for allele 2 (VIC), and green dots represent heterozygote (ab) or mixed genotypes identified with automatic SNP calling. The black squares show the no template control (NTC) using water instead of template DNA.

Figure 2

BLASTP protein comparison of the annotated sequence BC000036325 (http://www.cerealsdb.uk.net) with two forms of the general repressor of transcription, TaDr1B (BT009234) and TaDr1A (AF464903), and the TF TaNF-YB3 (BT009265), presented using CLC Main Workbench software.

Figure 3

Molecular phylogenetic tree of proteins encoded by Dr1 genes in monocot plants with the comparison to peptide sequences of TaNF-YB TFs in wheat. Rooted BioNJ dendrogram was generated by program SplitsTree4 (Huson and Bryant, 2006; http://www.splitstree.org). Scale bar shows uncorrected P genetic distance equivalent to 1.0. Accession sequences were retrieved from NCBI database. Plant species are coded as follows: Os, Oryza sativa; Ob, O. brachyantha; Sb, Sorghum bicolor; Zm, Zea mays; Si, Setaria italic; Ph, Panicum hallii; Ta, Triticum aestivum; Tu, T. urartu. The studying TaDr1 accession is indicated in Bold.

Figure 4

Expression of the reference gene Ta22845 (ATP-dependent 26S proteasome, regulatory subunit) and target genes, TaDr1, TaVrn1, and TaFT1, in leaves of eight wheat cultivars in response to drought. The expression levels of Ta22845 (A), TaDr1 (B), TaVrn1 (C), and TaFT1 (D) were calculated under drought relative to the corresponding controls in well-watered conditions. Eight wheat cultivars were studied, high-yielding are shown as darker boxes (1. Aktyubinka; 2. Albidum 188; 3. Altayskaya 110; and 4. Saratovskaya 60), and the four low-yielding cultivars are shown as framed light filled boxes (5. Vera; 6. Volgouralskaya; 7. Yugo-Vostochnaya 2; and 8. Zhenis). With the exception of Panel A, expression data were normalized using the averages of two reference genes, Ta22845 and Ta54825 (Actin), and presented as the average ± SE of three biological and two technical replicates for each genotype, experiment and treatment. Different letters above the bars indicate significant differences (p < 0.05) within each experiment calculated using ANOVA.