Nucleotide Polymorphism in the Wheat Transcriptional ActivatorSpaInfluences Its Pattern of Expression and Has Pleiotropic Effects on Grain Protein Composition, Dough Viscoelasticity, and Grain Hardness

Catherine Ravel,Nathalie Duchateau,Gilles Charmet,FrançOis Balfourier,Redouane El-Malki,Dominique Brunel,Mireille Dardevet,Isabelle Romeuf,Jacques Bordes,Pierre Martre

doi:10.1104/pp.109.146076

Catherine Ravel, Nathalie Duchateau + Show 8 more

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https://doi.org/10.1104/pp.109.146076

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Abstract

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.

Highlights

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
The synthesis of Grain storage protein (GSP) during grain filling is controlled by several mechanisms, including transcriptional and posttranscriptional modifications, but it is generally thought that GSPs are primarily regulated through a network of interacting transcription factors (TFs; Verdier and Thompson, 2008)
To assess the nucleotide diversity (p) of wheat Spa loci, Spa genes were amplified and sequenced from 42 wheat accessions sampled from the INRA worldwide core collection with the aim of maximizing the diver

Summary

Introduction

Storage protein activator (SPA) is a key regulator of the transcription of wheat (Triticum aestivum) grain storage protein genes and belongs to the Opaque transcription factor subfamily. Analysis of alleles at the 12 main GSP loci revealed a high level of genetic and biochemical diversity (Zhang et al, 2003, 2004; Ravel et al, 2006b), and direct relationships have been described between allelic variations at these loci and dough processing properties (Branlard et al, 2001; Bekes et al, 2006). This information is used in most wheat breeding programs. The PB and the AACA motif confer endosperm-specific expression (Colot et al, 1987; Yoshihara et al, 1996), whereas GLM is thought to play a role in the nutritional regulation of prolamin gene expression (Muller and Knudsen, 1993)

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