TubZIP28, a novel bZIP family transcription factor from Triticum urartu, and TabZIP28, its homologue from Triticum aestivum, enhance starch synthesis in wheat

Abstract

Summary Starch in wheat grain provides humans with carbohydrates and influences the quality of wheaten food. However, no transcriptional regulator of starch synthesis has been identified first in common wheat (Triticum aestivum) due to the complex genome. Here, a novel basic leucine zipper (bZIP) family transcription factor TubZIP28 was found to be preferentially expressed in the endosperm throughout grain‐filling stages in Triticum urartu, the A genome donor of common wheat. When TubZIP28 was overexpressed in common wheat, the total starch content increased by c. 4%, which contributed to c. 5% increase in the thousand kernel weight. The grain weight per plant of overexpression wheat was also elevated by c. 9%. Both in vitro and in vivo assays showed that TubZIP28 bound to the promoter of cytosolic AGPase and enhanced both the transcription and activity of the latter. Knockout of the homologue TabZIP28 in common wheat resulted in declines of both the transcription and activity of cytosolic AGPase in developing endosperms and c. 4% reduction of the total starch in mature grains. To the best of our knowledge, TubZIP28 and TabZIP28 are transcriptional activators of starch synthesis first identified in wheat, and they could be superior targets to improve the starch content and yield potential of wheat.

Comprehensive analysis of AGPase genes uncovers their potential roles in starch biosynthesis in lotus seed

“…For example, the G-box mutation in NnAGPL2a promoter may affect the binding and regulatory activity of some environmental stress responsive transcription factors in JX, such as MYC and bZIP genes [ 43 ]. In addition, G-box is also closely associated with regulation of starch biosynthesis process, for example, a previous study showed that G-box plays a role in regulation of SBE and AGPase gene expression [ 44 , 45 ]. Overall, these results partly reveal the genetic differentiation of NnAGPL2a and NnAGPS1a , and provide an important reference for identifying favored haplotype at the population level, which could be used in molecular breeding.…”

The NAC Transcription Factors OsNAC20 and OsNAC26 Regulate Starch and Storage Protein Synthesis

“…In addition, OsbZIP33 has also been inferred to play a role in regulation of starch synthesis as it is able to interact with the ACGT element buried in the promoter of SBEI and Wx (Cai et al, 2002). Recently, Song et al (2020) reported that TubZIP28 in Triticum urartu and its homolog, TabZIP28 from common wheat (Triticum aestivum), play a role in the regulation of starch synthesis as TubZIP28 binds to the promoter of cytosolic AGPase and enhances its transcription and activity. Apart from the above-mentioned regulators that directly bind to the promoters of starch synthesis-related genes to regulate their expression, some other regulators such as ZmaNAC36, ZmNAC34, rice starch regulator1 (RSR1), disulfide isomerase 1-2 protein (TaPDIL1-2), ZmMADS1a and G protein γ-subunit DEP1/qPE9-1 also have an indirect or unknown role in the regulation of starch synthesis (Fu and Xue, 2010;Zhang et al, 2014Zhang et al, , 2019aDong et al, 2019a,b;Peng et al, 2019).…”

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

“…Up till now, only a few TFs that regulate starch synthesis have been identified. 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]. For example, maize Opaque-2 (O2) indirectly represses the TF gene Prolamin-box binding factor (PBF); furthermore, O2 and PBF interact to regulate gene networks for starch and protein biosynthesis [14,27,28].…”