Cellular Localization of Wheat High Molecular Weight Glutenin Subunits in Transgenic Rice Grain

Transcriptome Analysis Reveals Potential Mechanism in Storage Protein Trafficking within Developing Grains of Common Wheat

Gluten proteins are the major storage protein fraction in the mature wheat grain. They are restricted to the starchy endosperm, which defines the viscoelastic properties of wheat dough. The synthesis of these storage proteins is controlled by the endoplasmic reticulum (ER) and is directed into the vacuole via the Golgi apparatus. In the present study, transcriptome analysis was used to explore the potential mechanism within critical stages of grain development of wheat cultivar "Shaannong 33" and its sister line used as the control (CK). Samples were collected at 10 DPA (days after anthesis), 14 DPA, 20 DPA, and 30 DPA for transcriptomic analysis. The comparative transcriptome analysis identified that a total of 18,875 genes were differentially expressed genes (DEGs) between grains of four groups "T10 vs. CK10, T14 vs. CK14, T20 vs. CK20, and T30 vs. CK30", including 2824 up-regulated and 5423 down-regulated genes in T30 vs. CK30. Further, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment highlighted the maximum number of genes regulating protein processing in the endoplasmic reticulum (ER) during grain enlargement stages (10-20 DPA). In addition, KEGG database analysis reported 1362 and 788 DEGs involved in translation, ribosomal structure, biogenesis, flavonoid biosynthesis pathway and intracellular trafficking, secretion, and vesicular transport through protein processing within ER pathway (ko04141). Notably, consistent with the higher expression of intercellular storage protein trafficking genes at the initial 10 DPA, there was relatively low expression at later stages. Expression levels of nine randomly selected genes were verified by qRT-PCR, which were consistent with the transcriptome data. These data suggested that the initial stages of "cell division" played a significant role in protein quality control within the ER, thus maintaining the protein quality characteristics at grain maturity. Furthermore, our data suggested that the protein synthesis, folding, and trafficking pathways directed by a different number of genes during the grain enlargement stage contributed to the observed high-quality characteristics of gluten protein in Shaannong 33 (Triticum aestivum L.).

Molecular characterization and expression of α-gliadin genes from wheat cultivar Dacke in Bg 250 rice variety

The main seed storage protein in wheat is gluten. It consists of gliadin and glutenins. Gluten gives high elasticity and extensibility during bread making, facilitating the formation of the dough. Rice is the staple food of Sri Lankans but, it has poor dough making ability compared to wheat. The aim of the present work was to characterize, clone and express α-gliadin in the T0 generation of Bg 250 rice variety as a preliminary step in improving the dough making ability of rice flour. Five α-gliadin recombinant pCR™2.1-TOPO® clones were selected for sequence analysis. Of the five clones, two functional genes and three pseudogenes were identified. Phylogenetic analysis revealed the two functional genes, (accession numbers KC660359 and KC660358) to be closely related to the α-gliadin genes of Triticum monococcum. The α-gliadin gene (KC660359) contained five cysteine residues, one less than the normal occurrence of cysteine residues in α-gliadin genes. To date there are no reports on expression of gliadin gene in transgenic rice. This novel gene was successfully expressed in the Sri Lankan rice variety Bg 250 under the control of the rice GluB-1 endosperm specific promoter.

Overexpressing wheat low-molecular-weight glutenin subunits in rice (Oryza sativa L. japonica cv. Koami) seeds

Genes encoding wheat low-molecular-weight glutenin subunits (LMW-GSs) that confer dough strength and extensibility were previously identified from Korean wheat cultivars. To improve low viscoelasticity of rice (Oryza sativa L.) dough caused by the lack of seed storage proteins comparable to wheat gluten, two genes, LMW03 and LMW28, encoding LMW-GSs are cloned from Korean wheat cultivar Jokyoung. The LMW genes are inserted into binary vectors under the control of the rice endosperm-specific Glu-B1 promoter. Transgenic rice plants expressing LMW03 or LMW28 in their seeds are generated using Agrobacterium-mediated transformation. The expression of recombinant wheat LMW-GS in the transgenic rice seeds was confirmed by SDS-PAGE and immunoblot analysis. Their accumulation in the endosperm and aleurone layers of rice seeds was observed through in situ immuno-hybridization.