Gluten quality of bread wheat is associated with activity of RabD GTPases

Abstract

In the developing endosperm of bread wheat (Triticum aestivum), seed storage proteins are produced on the rough endoplasmic reticulum (ER) and transported to protein bodies, specialized vacuoles for the storage of protein. The functionally important gluten proteins of wheat are transported by two distinct routes to the protein bodies where they are stored: vesicles that bud directly off the ER and transport through the Golgi. However, little is known about the processing of glutenin and gliadin proteins during these steps or the possible impact on their properties. In plants, the RabD GTPases mediate ER-to-Golgi vesicle transport. Available sequence information for Rab GTPases in Arabidopsis, rice, Brachypodium and bread wheat was compiled and compared to identify wheat RabD orthologs. Partial genetic sequences were assembled using the first draft of the Chinese Spring wheat genome. A suitable candidate gene from the RabD clade (TaRabD2a) was chosen for down-regulation by RNA interference (RNAi), and an RNAi construct was used to transform wheat plants. All four available RabD genes were shown by qRT-PCR to be down-regulated in the transgenic developing endosperm. The transgenic grain was found to produce flour with significantly altered processing properties when measured by farinograph and extensograph. SE-HPLC found that a smaller proportion of HMW-GS and large proportion of LMW-GS are incorporated into the glutenin macropolymer in the transgenic dough. Lower protein content but a similar protein profile on SDS-PAGE was seen in the transgenic grain.

Transcriptome-wide identification and characterization of the Rab GTPase family in mango

“…Analyses of sequence similarities and of the presence of specific family and subfamily conserved motifs in their sequence allowed the identification of the closest homologues from Arabidopsis and the assignment of these sequences to members of the Rab family. The Rab sequences do not cluster in a species specific manner but rather within subfamilies supporting the findings of previous authors [41,46]. According to these authors, it can be speculated that the members of the same cluster display similar functions.…”

“…Comparison between the 'CK' and the 'P' group at the same ripening stage (unripe or ripe stage) revealed significantly higher levels in the 'P' group. Evidence from wheat has shown that transgenic lines with down-regulated RabD gene resulted in grains with altered bread making quality [46]. These authors suggested that the reduced bread making quality observed in the transgenic grains might have been due to the altered trafficking of the gluten proteins.…”

Impact of Altered Cell Wall Composition on Saccharification Efficiency in Stem Tissue of Arabidopsis RABA GTPase-Deficient Knockout Mutants

“…The RABA family of genes is widespread across a range of plant phyla including wheat, rice and maize [29,30]. Thus, lines in which activities of the RABA4 orthologues in these species have been inhibited may have considerable commercial relevance, especially considering the additional fact that these genetic modifications do not appear to adversely impact on the yield of biomass or its total glucose content.…”

Gene Expression and Proteomics Studies Suggest an Involvement of Multiple Pathways Under Day and Day–Night Combined Heat Stresses During Grain Filling in Wheat

“…The present study has also observed very low expression of other regulatory genes related to protein trafficking throughout the seed development (Rab GTPases), indicating their improper regulation under stress conditions. Tyler et al (2015) also showed decreased expression of Rab GTPases under heat stress, thus stopping the regulation of vesicles carrying seed storage proteins from endoplasmic reticulum to Golgi complex. To sum up, heat stress has enhanced various stress-responsive genes and proteins but cannot maintain their expression under prolonged stress duration.…”