Abstract
Starch and prolamin composition and content are important indexes for determining the processing and nutritional quality of wheat (Triticum aestivum L.) grains. Several transcription factors (TFs) regulate gene expression during starch and protein biosynthesis in wheat. Storage protein activator (TaSPA), a member of the basic leucine zipper (bZIP) family, has been reported to activate glutenin genes and is correlated to starch synthesis related genes. In this study, we generated TaSPA-B overexpressing (OE) transgenic wheat lines. Compared with wild-type (WT) plants, the starch content was slightly reduced and starch granules exhibited a more polarized distribution in the TaSPA-B OE lines. Moreover, glutenin and ω- gliadin contents were significantly reduced, with lower expression levels of related genes (e.g., By15, Dx2, and ω-1,2 gliadin gene). RNA-seq analysis identified 2023 differentially expressed genes (DEGs). The low expression of some DEGs (e.g., SUSase, ADPase, Pho1, Waxy, SBE, SSI, and SS II a) might explain the reduction of starch contents. Some TFs involved in glutenin and starch synthesis might be regulated by TaSPA-B, for example, TaPBF was reduced in TaSPA-B OE-3 lines. In addition, dual-luciferase reporter assay indicated that both TaSPA-B and TaPBF could transactivate the promoter of ω-1,2 gliadin gene. These results suggest that TaSPA-B regulates a complex gene network and plays an important role in starch and protein biosynthesis in wheat.
Highlights
Bread wheat (Triticum aestivum L.), one of the three major food crops, provides a quarter of the world’s supply of plant proteins, carbohydrates, and dietary fiber [1,2]
This study contributes a better understanding of the role of TaSPA-B in prolamin and starch accumulation in wheat grains
We obtained six independent transformants, which were confirmed by PCR and sequencing analysis (Figure 1A)
Summary
Bread wheat (Triticum aestivum L.), one of the three major food crops, provides a quarter of the world’s supply of plant proteins, carbohydrates, and dietary fiber [1,2]. AP2, bZIP, and NAC TFs regulate starch synthesis related genes (SSRGs) in rice (Oryza sativa), maize (Zea mays) and wheat [11,12,23,24,25,26,27]. Maize Opaque-2 (O2) indirectly represses the TF gene Prolamin-box binding factor (PBF); O2 and PBF interact to regulate gene networks for starch and protein biosynthesis [14,27,28]. The regulatory mechanism underlying the TFs and gene networks becomes a hot topic in wheat grain research [13,17,19,27,33,34]. This study contributes a better understanding of the role of TaSPA-B in prolamin and starch accumulation in wheat grains
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