Trafficking of storage proteins in developing grain of wheat

Abstract

The processing properties of the wheat flour are largely determined by the structures and interactions of the grain storage proteins (also called gluten proteins) which form a continuous visco-elastic network in dough. Wheat gluten proteins are classically divided into two groups, the monomeric gliadins and the polymeric glutenins, with the latter being further classified into low molecular weight (LMW) and high molecular weight (HMW) subunits. The synthesis, folding and deposition of the gluten proteins take place within the endomembrane system of the plant cell. However, determination of the precise routes of trafficking and deposition of individual gluten proteins in developing wheat grain has been limited in the past by the difficulty of developing monospecific antibodies. To overcome this limitation, a single gluten protein (a LMW subunit) was expressed in transgenic wheat with a C-terminal epitope tag, allowing the protein to be located in the cells of the developing grain using highly specific antibodies. This approach was also combined with the use of wider specificity antibodies to compare the trafficking and deposition of different gluten protein groups within the same endosperm cells. These studies are in agreement with previous suggestions that two trafficking pathways occur in wheat, with the proteins either being transported via the Golgi apparatus into the vacuole or accumulating directly within the lumen of the ER. They also suggest that the same individual protein could be trafficked by either pathway, possibly depending on the stage of development, and that segregation of gluten proteins both between and within protein bodies may occur.

In silico identification and analysis of the protein disulphide isomerases in wheat and rice

“…The seed storage protein deposition processes in wheat and rice typically involve: (i) targeting of the nascent polypeptides to the ER lumen; (ii) their folding, followed by assortment and assembly of the appropriate types of polypeptides into protein bodies (PB); and (iii) deposition of the PBs into the endosperm cells by two simultaneous pathways: the standard pathway, via Golgi to the protein storage vacuole (PSV), or accumulation directly into PBs in the ER lumen (Shewry & Halford 2002;Herman & Schmidt 2004;Vitale & Ceriotti 2004;Tosi et al 2009). These complex events, carried out over a period of a few days, clearly indicate the need for 'foldase' catalysts and chaperones.…”

Polymerisation of gluten proteins in developing wheat grain as affected by desiccation

“…However, their proportion decreased rapidly from 10 to 15 DAA, when the synthesis of gluten proteins started, and they accounted for about 20% of total grain proteins at the end of the protein accumulation phase. As according to Tosi et al (2009), synthesis of gluten proteins starts at about 8 DAA, it was expected that grain harvested at 10 DAA would have a very low content of gluten proteins, and their proportion at this stage was about 12-15% of total grain proteins in our study. Both gliadins and glutenins were accumulated rapidly until 35 DAA with gliadins being accumulated faster than glutenins.…”

“…Gliadins contribute to the viscosity, while glutenin polymers contribute to the elasticity of wheat dough. Tosi et al (2009) observed gluten protein bodies in developing grain as early as 8 days after anthesis (DAA). Shewry et al (2009) reported that low molecular weight-glutenin subunits (LMW-GS) and gliadins were synthesised and accumulated most rapidly between 12 DAA and 35 DAA, while high molecular weight-glutenin subunits (HMW-GS) accumulated more slowly but for a longer period during grain filling.…”

Synthesis and accumulation of glutenin subunits during grain development in bread wheat as revealed by reversed-phase ultra-performance liquid chromatography (RP-UPLC)

“…The glutenins are typical secretory proteins synthesized in polyribosomes and attached to rough endoplasmic reticulum (ER) in where disulfide bond formation, glutenin protein folding and maturation occur under the help of ER lumenal proteins such as molecular chaperone proteins disulfide isomerase (PDI) and binding protein (BiP) (Bollini and Chrispeels 1979;Shewry 1999;Tosi et al 2009). PDI gene family containing thioredoxin domains is involved in the correct formation of disulphide bond, protein folding and assembling of protein bodies.…”