Abstract
The wild wheat Aegilops tauschii Coss. has extensive natural variation available for breeding of common wheat. Drought stress tolerance is closely related to abscisic acid (ABA) sensitivity. In this study, 17 synthetic hexaploid wheat lines, produced by crossing the tetraploid wheat cultivar Langdon with 17 accessions of Ae. tauschii, were used for comparative analysis of natural variation in drought tolerance and ABA sensitivity. Ae. tauschii showed wide natural variation, with weak association between the traits. Drought-sensitive accessions of Ae. tauschii exhibited significantly less ABA sensitivity. D-genome variations observed at the diploid genome level were not necessarily reflected in synthetic wheats. However, synthetic wheats derived from the parental Ae. tauschii accessions with high drought tolerance were significantly more tolerant to drought stress than those from drought-sensitive accessions. Moreover, synthetic wheats with high drought tolerance showed significantly higher ABA sensitivity than drought-sensitive synthetic lines. In the hexaploid genetic background, therefore, weak association of ABA sensitivity with drought tolerance was observed. To study differences in gene expression patterns between stress-tolerant and -sensitive lines, levels of two Cor/Lea and three transcription factor gene transcripts were compared. The more tolerant accession of Ae. tauschii tended to accumulate more abundant transcripts of the examined genes than the sensitive accession under stress conditions. The expression patterns in the synthetic wheats seemed to be additive for parental lines exposed to drought and ABA treatments. However, the transcript levels of transcription factor genes in the synthetic wheats did not necessarily correspond to the postulated levels based on expression in parental lines. Allopolyploidization altered the expression levels of the stress-responsive genes in synthetic wheats.
Highlights
Abiotic stress signal pathways have been studied using artificially generated mutants in the model plant Arabidopsis thaliana
Hexaploid synthetic wheat lines can be artificially produced through allopolyploidization between tetraploid wheat and Ae. tauschii [39,40], implying that agronomically important genes from natural variation of the Ae. tauschii population are available for wheat breeding by making synthetic wheats
The synthetic wheats derived from the parental Ae. tauschii accessions with high drought tolerance were significantly more tolerant to drought stress than those from the drought-sensitive accessions (Figure 3C)
Summary
Abiotic stress signal pathways have been studied using artificially generated mutants in the model plant Arabidopsis thaliana. Occurring variants are useful in determining which specific allelic variants exist in nature, where they might either be neutral or have a selective advantage under specific conditions [1] Abiotic stresses such as drought, temperature and salinity reduce yield of common wheat (Triticum aestivum L.). Many low temperatureand drought-inducible genes contain both C-repeat (CRT)/dehydration-responsive element (DRE) and ABA-responsive element (ABRE) motifs in their promoters, and these cis elements are considered to function independently. Expression of these Cor/Lea genes is regulated by major transcription factors in the CBF/DREB and AREB/ABF families under abiotic stress conditions such as low temperature and osmotic stress [6]
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