Storage protein activator (SPA) is a key regulator of the transcription of wheat (Triticum aestivum) grain storage protein genes and belongs to the Opaque2 transcription factor subfamily. We analyzed the sequence polymorphism of the three homoeologous Spa genes in hexaploid wheat. The level of polymorphism in these genes was high particularly in the promoter. The deduced protein sequences of each homoeolog and haplotype show greater than 93% identity. Two major haplotypes were studied for each Spa gene. The three Spa homoeologs have similar patterns of expression during grain development, with a peak in expression around 300 degree days after anthesis. On average, Spa-B is 10 and seven times more strongly expressed than Spa-A and Spa-D, respectively. The haplotypes are associated with significant quantitative differences in Spa expression, especially for Spa-A and Spa-D. Significant differences were found in the quantity of total grain nitrogen allocated to the gliadin protein fractions for the Spa-A haplotypes, whereas the synthesis of glutenins is not modified. Genetic association analysis between Spa and dough viscoelasticity revealed that Spa polymorphisms are associated with dough tenacity, extensibility, and strength. Except for Spa-A, these associations can be explained by differences in grain hardness. No association was found between Spa markers and the average single grain dry mass or grain protein concentration. These results demonstrate that in planta Spa is involved in the regulation of grain storage protein synthesis. The associations between Spa and dough viscoelasticity and grain hardness strongly suggest that Spa has complex pleiotropic functions during grain development.
Arabinoxylans (AX) are major components of cell walls in wheat endosperm. The water-extractable part, WEAX, is considered as dietary fibres with health promoting effects. AX exhibit large natural variations in their amount but few studies have been carried out on the genetics of WEAX content and structure in bread wheat. We first carried out a "forward'' quantitative genetic approach, using two recombinant populations derived from crosses between WEAX-high and WEAX-low parents and the viscosity of flour extract (WEAX-viscosity) as a predictor of WEAX content. This allowed us to identify two QTL regions, one of them, found on chromosome 6B in both populations, having a major effect with as much as 59% of the phenotypic variation explained by a single QTL. Then, we focused on key enzymes involved in the biosynthetic pathway of arabinoxylans. Out of 34 homoeologous candidate genes studied by sequencing a set of 46 lines, representing a worldwide diversity 179 show no polymorphi! sm. In the 16 polymorphic candidate genes, 80 SNP (in 15 genes) and 16 indels (in 4 genes) were detected. Then 27 SNP (in 13 genes) were genotyped in a larger collection of 156 lines (Healthgrain diversity screen). Eight associations were significant at an indicative 5% threshold, but only one, between COMT (Caffeic acid O methyltransferase) on chromosome 7A and A/X in WEAX was significant at a 1% level. The usefulness of these approaches and preliminary results for breeding is discussed
BackgroundTranscription factors (TFs) regulate gene expression by interacting with promoters of their target genes and are classified into families based on their DNA-binding domains. Genes coding for TFs have been identified in the sequences of model plant genomes. The rice (Oryza sativa spp. japonica) genome contains 2,384 TF gene models, which represent the mRNA transcript of a locus, classed into 63 families.ResultsWe have created an extensive list of wheat (Triticum aestivum L) TF sequences based on sequence homology with rice TFs identified and classified in the Database of Rice Transcription Factors (DRTF). We have identified 7,112 wheat sequences (contigs and singletons) from a dataset of 1,033,960 expressed sequence tag and mRNA (ET) sequences available. This number is about three times the number of TFs in rice so proportionally is very similar if allowance is made for the hexaploidy of wheat. Of these sequences 3,820 encode gene products with a DNA-binding domain and thus were confirmed as potential regulators. These 3,820 sequences were classified into 40 families and 84 subfamilies and some members defined orphan families. The results were compiled in the Database of Wheat Transcription Factor (wDBTF), an inventory available on the web http://wwwappli.nantes.inra.fr:8180/wDBFT/. For each accession, a link to its library source and its Affymetrix identification number is provided. The positions of Pfam (protein family database) motifs were given when known.ConclusionswDBTF collates 3,820 wheat TF sequences validated by the presence of a DNA-binding domain out of 7,112 potential TF sequences identified from publicly available gene expression data. We also incorporated in silico expression data on these TFs into the database. Thus this database provides a major resource for systematic studies of TF families and their expression in wheat as illustrated here in a study of DOF family members expressed during seed development.
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