Over-Expressing TaSPA-B Reduces Prolamin and Starch Accumulation in Wheat (Triticum aestivum L.) Grains

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.

Starch biosynthesis in cereal endosperms: An updated review over the last decade

“…OsbZIP58 and RPBF also directly regulate the expression of the gene encoding lysine ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH), a key regulator of free lysine content in plants ( Kawakatsu and Takaiwa, 2010 ). Similar conclusions were also obtained with the O2 and PBF homologs in wheat and barley ( Guo et al., 2020b ; Orman-Ligeza et al., 2020 ).…”

RNAi silencing of wheat gliadins alters the network of transcription factors that regulate the synthesis of seed storage proteins toward maintaining grain protein levels

“…However, the rest of the TFs listed in Supplementary Table 7 were not DE in the grain of E82, and therefore they may not be relevant for explaining the rearrangements in the regulation of the SSP and starch synthesis genes in the E82 line. The expression of homeologs of the TaSPA , which has a key role in the biosynthesis of prolamins and starch ( Guo et al, 2020 ), was not over the threshold to be included in the DGE analysis.…”

“…They are coded by starch synthesis-related genes (SSRGs) and they are regulated by TFs as bZIPs and NACs ( Wang et al, 2013 ; Zhang et al, 2019 ). In addition, there are TFs actively involved in the regulation of both SSPs and SSRGs, like TaSPA and TaPBF in wheat, or O2 and PBF in maize ( Zhang et al, 2016 ; Guo et al, 2020 ; Orman-Ligeza et al, 2020 ).…”

High-Molecular-Weight Glutenin Subunits: Genetics, Structures, and Relation to End Use Qualities

“…Some conserved cis -acting elements related to the expression of storage proteins have been identified in HMW-GS gene promoters [ 47 , 48 , 49 , 50 ]. To date, storage protein activator (SPA), a member of the basic leucine zipper (bZIP) family, has been identified to play a key role in the regulation of wheat grain storage protein synthesis [ 51 , 52 , 53 , 54 , 55 ]. From a theoretical point of view, the hexaploid wheat cultivars could express 6 different HMW-GSs, 1Ax, 1Ay, 1Bx, 1By, 1Dx, and 1Dy, while in fact, owing to gene silencing, almost all of them express 3 to 5 HMW-GSs depending on wheat cultivars except the few hexaploid wheat cultivars expressing all 6 HMW-GSs [ 56 , 57 , 58 ].…”