Abstract
BackgroundUDP-glucose: glycoprotein glucosyltransferase (UGGT) is a key player in the quality control mechanism (ER-QC) that newly synthesized glycoproteins undergo in the ER. It has been shown that the UGGT Arabidopsis orthologue is involved in ER-QC; however, its role in plant physiology remains unclear.ResultsHere, we show that two mutant alleles in the At1g71220 locus have none or reduced UGGT activity. In wild type plants, the AtUGGT transcript levels increased upon activation of the unfolded protein response (UPR). Interestingly, mutants in AtUGGT exhibited an endogenous up–regulation of genes that are UPR targets. In addition, mutants in AtUGGT showed a 30 % reduction in the incorporation of UDP-Glucose into the ER suggesting that this enzyme drives the uptake of this substrate for the CNX/CRT cycle. Plants deficient in UGGT exhibited a delayed growth rate of the primary root and rosette as well as an alteration in the number of leaves. These mutants are more sensitive to pathogen attack as well as heat, salt, and UPR-inducing stressors. Additionally, the plants showed impairment in the establishment of systemic acquired resistance (SAR).ConclusionsThese results show that a lack of UGGT activity alters plant vegetative development and impairs the response to several abiotic and biotic stresses. Moreover, our results uncover an unexpected role of UGGT in the incorporation of UDP-Glucose into the ER lumen in Arabidopsis thaliana.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0525-2) contains supplementary material, which is available to authorized users.
Highlights
UDP-glucose: glycoprotein glucosyltransferase (UGGT) is a key player in the quality control mechanism (ER-QC) that newly synthesized glycoproteins undergo in the endoplasmic reticulum (ER)
Arabidopsis thaliana ER-enriched fractions exhibit UGGT activity The UGGT activity has been measured in mung bean [9], and its role in protein quality control in the ER has been determined based on genetic analyses in Arabidopsis thaliana [14,15,16]
Using UDP-[14C]Glc and denatured soybean agglutinin (SBA, a glycoprotein that contains mainly Man9GlcNAc2 oligosaccharides) as substrates, we found that ER-enriched fractions from Arabidopsis thaliana increased the incorporation of the radioactive label into TCA-insoluble material
Summary
UDP-glucose: glycoprotein glucosyltransferase (UGGT) is a key player in the quality control mechanism (ER-QC) that newly synthesized glycoproteins undergo in the ER. A significant portion of these proteins are Nglycosylated at an asparagine residue that is present in the consensus sequence -N-X-S/T- (where X is any amino acid except proline). This glycosylation occurs as they are translocated to the ER lumen by the reaction catalyzed by the enzyme oligosaccharyltransferase from. The CNX and CRT are lectin/chaperones that bind the monoglucosylated oligosaccharides (GlcMan9GlcNAc2) present on N-glycosylated proteins they retain the proteins at the ER while they go through the folding process. The protein is again bound by CNX or CRT and retained in the ER to continue with the folding process. Cycles of glucosylation-binding to CNX/ CRT-deglucosylation continue until the glycoprotein folds or is targeted for degradation [8]
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