Molecular cloning, phylogenetic analysis, and expression profiling of endoplasmic reticulum molecular chaperone BiP genes from bread wheat (Triticum aestivum L.)

Mechanical effect of protein glycosylation on BiP-mediated post-translational translocation and folding in the endoplasmic reticulum

About one-third of the proteins synthesized in eukaryotic cells are directed to the secretory pathway, where close to 70% are being N-glycosylated. N-glycosylation is a crucial modification for various cellular processes, including endoplasmic reticulum (ER) glycoprotein folding quality control, lysosome delivery, and cell signaling. The defects in N-glycosylation can lead to severe developmental diseases. For the proteins to be glycosylated, they must be translocated to the ER through the Sec61 translocon channel, either via co-translationally or post-translationally. N-glycosylation not only could accelerate post-translational translocation but may also enhance protein stability, while protein folding can assist in their movement into the ER. However, the precise mechanisms by which N-glycosylation and folding influence translocation remain poorly understood. The chaperone BiP is essential for post-translational translocation, using a "ratchet" mechanism to facilitate protein entry into the ER. Although research has explored how BiP interacts with protein substrates, there has been less focus on its binding to glycosylated substrates. Here, we review the effect of N-glycosylation on protein translocation, employing single-molecule studies and ensembles approaches to clarify the roles of BiP and N-glycosylation in these processes. Our review explores the possibility of a direct relationship between translocation and a ratchet effect of glycosylation and the importance of BiP in binding glycosylated proteins for the ER quality control system.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-025-01313-x.

BiP Proteins from Symbiodiniaceae: A "Shocking" Story

More than four decades ago, the discovery of a companion protein of immunoglobulins in myeloma cells and soon after, of their ability to associate with heavy chains, made the term immunoglobulin binding protein (BiP) emerge, prompting a tremendous amount of effort to understand their versatile cellular functions. BiPs belong to the heat shock protein (Hsp) 70 family and are crucial for protein folding and cellular stress responses. While extensively studied in model organisms such as Chlamydomonas, their roles in dinoflagellates, especially in photosynthetic Symbiodiniaceae, remain largely underexplored. Given the importance of Symbiodiniaceae-cnidarian symbiosis, critical for the sustaining of coral reef ecosystems, understanding the contribution of Hsps to stress resilience is essential; however, most studies have focused on Hsps in general but none on BiPs. Moreover, despite the critical role of light in the physiology of these organisms, research on light effects on BiPs from Symbiodiniaceae has also been limited. This review synthesizes the current knowledge from the literature and sequence data, which reveals a high degree of BiP conservation at the gene, protein, and structural levels in Symbiodiniaceae and other dinoflagellates. Additionally, we show the existence of a potential link between circadian clocks and BiP regulation, which would add another level of regulatory complexity. The evolutionary relationship among dinoflagellates overall suggests conserved functions and regulatory mechanisms, albeit expecting confirmation by experimental validation. Finally, our analysis also highlights the significant knowledge gap and underscores the need for further studies focusing on gene and protein regulation, promoter architecture, and structural conservation of Symbiodiniaceae and dinoglagellate BiPs in general. These will deepen our understanding of the role of BiPs in the Symbiodiniaceae-cnidarian interactions and dinoflagellate physiology.

Biochemical and molecular characterization of the SBiP1 chaperone from Symbiodinium microadriaticum CassKB8 and light parameters that modulate its phosphorylation

The coding and promoter region sequences from the BiP-like protein SBiP1 from Symbiodinium microadriaticum CassKB8 were obtained by PCR, sequenced and compared with annotated sequences. The nucleotides corresponding to the full sequence were correctly annotated and the main SBiP1 features determined at the nucleotide and amino acid level. The translated protein was organized into the typical domains of the BiP/HSP70 family including a signal peptide, a substrate- and a nucleotide-binding domain, and an ER localization sequence. Conserved motifs included a highly conserved Thr513 phosphorylation site and two ADP-ribosylation sites from eukaryotic BiP's. Molecular modeling showed the corresponding domain regions and main exposed post-translational target sites in its three-dimensional structure, which also closely matched Homo sapiens BiP further indicating that it indeed corresponds to a BiP/HSP70 family protein. The gene promoter region showed at least eight light regulation-related sequences consistent with the molecule being highly phosphorylated in Thr under dark conditions and dephosphorylated upon light stimuli. We tested light parameter variations that could modulate the light mediated phosphorylation effect and found that SBiP1 Thr dephosphorylation was only significantly detected after 15-30 min light stimulation. Such light-induced dephosphorylation was observed even when dichlorophenyl dimethyl urea, a photosynthesis inhibitor, was also present in the cells during the light stimulation. Dephosphorylation occurred indistinctly under red, yellow, blue or the full visible light spectra. In additon, it was observed at a light intensity of as low as 1 μmole photon m-2 s-1. Our results indicate that: a) SBiP1 is a chaperone belonging to the BiP/HSP70 family proteins; b) its light-modulated phosphorylation/dephosphorylation most likely functions as an activity switch for the chaperone; c) this light-induced modulation occurs relatively slow but is highly sensitive to the full spectrum of visible light; and d) the light induced Thr dephosphorylation is independent of photosynthetic activity in these cells.

Overexpression of PvBiP2 improved biomass yield and cadmium tolerance in switchgrass (Panicum virgatum L.)

Switchgrass (Panicum virgatum L.), the prime bioenergy feedstock crop, is one ideal candidate for phytoremediation of cadmium (Cd). The absorption of Cd imposes severe endoplasmic reticulum (ER)-stress in plants. ER chaperone binding proteins (BiPs) are important modulators in ER-stress responses. The objective of this study was to characterize one Cd-responsive BiP gene, PvBiP2, in switchgrass for its roles in Cd tolerance and plant growth. PvBiP2 was up-regulated by Cd and the ER-stress inducer, dithiothreitol (DTT) and could be trans-activated by one Cd-responsive heat shock transcription factor PvHsfA4. Overexpression of PvBiP2 in switchgrass significantly increased its plant growth with higher height, stem diameter, leaf width, internode length, and tiller numbers than those of the wildtype (WT) plants under non-stress conditions. After 30 days of Cd treatment, the PvBiP2 over-expression transgenic lines showed 40-45% higher dry biomass accumulation with net photosynthesis rate (Pn), but lower electrolyte leakage (EL), malondialdehyde (MDA), and glutathione (GSH) levels than WT. Moreover, over-expressing PvBiP2 led to ∼90-140% Cd accumulation in plants but 46-57% lower Cd translocation rates to shoots. Together, the PvHSFA4-PvBiP2 module acted as positive regulators in plant Cd tolerance, and over-expressing PvBiP2 promoted plant vegetative growth as well as Cd tolerance making it an ideal molecular target for genetic improvement in switchgrass in the future.

Consensus genomic regions associated with grain protein content in hexaploid and tetraploid wheat

A meta-analysis of QTLs associated with grain protein content (GPC) was conducted in hexaploid and tetraploid wheat to identify robust and stable meta-QTLs (MQTLs). For this purpose, as many as 459 GPC-related QTLs retrieved from 48 linkage-based QTL mapping studies were projected onto the newly developed wheat consensus map. The analysis resulted in the prediction of 57 MQTLs and 7 QTL hotspots located on all wheat chromosomes (except chromosomes 1D and 4D) and the average confidence interval reduced 2.71-fold in the MQTLs and QTL hotspots compared to the initial QTLs. The physical regions occupied by the MQTLs ranged from 140 bp to 224.02 Mb with an average of 15.2 Mb, whereas the physical regions occupied by QTL hotspots ranged from 1.81 Mb to 36.03 Mb with a mean of 8.82 Mb. Nineteen MQTLs and two QTL hotspots were also found to be co-localized with 45 significant SNPs identified in 16 previously published genome-wide association studies in wheat. Candidate gene (CG) investigation within some selected MQTLs led to the identification of 705 gene models which also included 96 high-confidence CGs showing significant expressions in different grain-related tissues and having probable roles in GPC regulation. These significantly expressed CGs mainly involved the genes/gene families encoding for the following proteins: aminotransferases, early nodulin 93, glutamine synthetases, invertase/pectin methylesterase inhibitors, protein BIG GRAIN 1-like, cytochrome P450, glycosyl transferases, hexokinases, small GTPases, UDP-glucuronosyl/UDP-glucosyltransferases, and EamA, SANT/Myb, GNAT, thioredoxin, phytocyanin, and homeobox domains containing proteins. Further, eight genes including GPC-B1, Glu-B1-1b, Glu-1By9, TaBiP1, GSr, TaNAC019-A, TaNAC019-D, and bZIP-TF SPA already known to be associated with GPC were also detected within some of the MQTL regions confirming the efficacy of MQTLs predicted during the current study.

Cuticular Wax Modification by Epichloë Endophyte in Achnatherum inebrians under Different Soil Moisture Availability

The cuticular wax serves as the outermost hydrophobic barrier of plants against nonstomatal water loss and various environmental stresses. An objective of this study was to investigate the contribution of the mutualistic fungal endophyte Epichloë gansuensis to leaf cuticular wax of Achnatherum inebrians under different soil moisture availability. Through a pot experiment and gas chromatography−mass spectrometry (GC−MS) analysis, our results indicated that the hydrocarbons were the dominant components of leaf cuticular wax, and the proportion of alcohols, aldehydes, amines, and ethers varied with the presence or absence of E. gansuensis and different soil moisture availability. Amines and ethers are unique in endophyte-free (EF) A. inebrians plants and endophyte-infected (EI) A. inebrians plants, respectively. By transcriptome analysis, we found a total of 13 differentially expressed genes (DEGs) related to cuticular biosynthesis, including FabG, desB, SSI2, fadD, BiP, KCS, KAR, FAR, and ABCB1. A model is proposed which provides insights for understanding cuticular wax biosynthesis in the association of A. inebrians plants with E. gansuensis. These results may help guide the functional analyses of candidate genes important for improving the protective layer of cuticular wax of endophyte-symbiotic plants.

Reducing Nitrogen Rate and Increasing Plant Density Accomplished High Yields with Satisfied Grain Quality of Soft Wheat via Modifying the Free Amino Acid Supply and Storage Protein Gene Expression

In a 2 yr field experiment, we investigated the combined effects of reduced nitrogen (N) rate and increased plant density on the trade-off between the grain protein content (GPC) and the grain yield (GY) in soft wheat cultivars. Reducing N application significantly decreased both GPC and GY; however, to some extent, increasing the top-dressed N ratio and plant density compensated for the GY loss. Optimizing the combination of these three factors (150 kg N ha^-1 with 50% top-dressed N and 360 × 10⁴ plants ha^-1) achieved both the required lower GPC for soft wheat and relatively higher GY compared with the conventional cultivation strategy. In addition, this optimized combination downregulated 11 high-molecular-weight glutenin subunits, 8 low-molecular-weight glutenin subunits, 5 α/β-gliadins, and 2 γ-gliadins in mature grains as identified by data-independent acquisition mass spectrometry. Further analysis indicated that the relatively lower free amino acid content and downregulated expressions of the seed storage protein (SSP) synthesis-related genes in filling grains contributed to the reduction of SSP and GPC. Furthermore, the dilution effect induced by a relatively higher accumulation of starch than proteins also partially explained the reduced GPC. Unlike proteins, grain starch accumulation and content depended more on the soluble sugar availability, rather than on the starch synthesis capacity. These findings provide novel insights on simultaneous improvement in the grain quality and yield of soft wheat through synchronized manipulations of N fertilization and plant density.

Comparison of the Agronomic, Cytological, Grain Protein Characteristics, as Well as Transcriptomic Profile of Two Wheat Lines Derived From Wild Emmer

Two advanced wheat lines BAd7-209 and BAd23-1 without the functional gene GPC-B1 were obtained from a cross between common wheat cultivar Chuannong 16 (CN16) and wild emmer wheat accession D97 (D97). BAd7-209 showed superior quality parameters than those of BAd23-1 and CN16. We found that the components of glutenins and gliadins in BAd7-209 and BAd23-1 were similar, whereas BAd7-209 had higher amount of glutenins and gliadins than those of BAd23-1. RNA sequencing analysis on developing grains of BAd7-209 and BAd23-1 as well as their parents revealed 382 differentially expressed genes (DEGs) between the high–grain protein content (GPC) (D97 + BAd7-209) and the low-GPC (CN16 + BAd23-1) groups. DEGs were mainly associated with transcriptional regulation of the storage protein genes, protein processing in endoplasmic reticulum, and protein export pathways. The upregulated gluten genes and transcription factors (e.g., NAC, MYB, and bZIP) may contribute to the high GPC in BAd7-209. Our results provide insights into the potential regulation pathways underlying wheat grain protein accumulation and contribute to make use of wild emmer for wheat quality improvement.

Crosstalk during the Carbon-Nitrogen Cycle That Interlinks the Biosynthesis, Mobilization and Accumulation of Seed Storage Reserves

Carbohydrates are the major storage reserves in seeds, and they are produced and accumulated in specific tissues during the growth and development of a plant. The storage products are hydrolyzed into a mobile form, and they are then translocated to the developing tissue following seed germination, thereby ensuring new plant formation and seedling vigor. The utilization of seed reserves is an important characteristic of seed quality. This review focuses on the seed storage reserve composition, source–sink relations and partitioning of the major transported carbohydrate form, i.e., sucrose, into different reserves through sucrolytic processes, biosynthetic pathways, interchanging levels during mobilization and crosstalk based on vital biochemical pathways that interlink the carbon and nitrogen cycles. Seed storage reserves are important due to their nutritional value; therefore, novel approaches to augmenting the targeted storage reserve are also discussed.

Proteome and transcriptome analyses of wheat near isogenic lines identifies key proteins and genes of wheat bread quality

The regulation of wheat protein quality is a highly complex biological process involving multiple metabolic pathways. To reveal new insights into the regulatory pathways of wheat glutenin synthesis, we used the grain-filling period wheat grains of the near-isogenic lines NIL-723 and NIL-1010, which have large differences in quality, to perform a combined transcriptome and proteome analysis. Compared with NIL-1010, NIL-723 had 1287 transcripts and 355 proteins with significantly different abundances. Certain key significantly enriched pathway were identified, and wheat quality was associated with alanine, aspartate and glutamate metabolism, nitrogen metabolism and alpha-linolenic acid metabolism. Differentially expressed proteins (DEPs) or Differentially expressed genes (DEGs) in amino acid synthesis pathways were upregulated primarily in the glycine (Gly), methionine (Met), threonine (Thr), glutamic acid (Glu), proline (proC), cysteine (Cys), and arginine (Arg) synthesis and downregulated in the tryptophan (trpE), leucine (leuC), citrulline (argE), and ornithine (argE) synthesis. Furthermore, to elucidate changes in glutenin in the grain synthesis pathway, we plotted a regulatory pathway map and found that DEGs and DEPs in ribosomes (RPL5) and the ER (HSPA5, HYOU1, PDIA3, PDIA1, Sec24, and Sec31) may play key roles in regulating glutenin synthesis. The transcriptional validation of some of the differentially expressed proteins through real-time quantitative PCR analysis further validated the transcriptome and proteomic results.

The Endoplasmic Reticulum Role in the Plant Response to Abiotic Stress

The endoplasmic reticulum (ER) is the organelle where one third of the proteins of a cell are synthetized. Several of these proteins participate in the signaling and response of cells, tissues, or from the organism to the environment. To secure the proper synthesis and folding of these proteins, or the disposal of unfolded or misfolded proteins, the ER has different mechanisms that interact and regulate each other. These mechanisms are known as the ER quality control (ERQC), ER-associated degradation (ERAD) and the unfolded protein response (UPR), all three participants of the maintenance of ER protein homeostasis or proteostasis. Given the importance of the client proteins of these ER mechanisms in the plant response to the environment, it is expected that changes or alterations on their components have an impact on the plant response to environmental cues or stresses. In this mini review, we focus on the impact of the alteration of components of ERQC, ERAD and UPR in the plant response to abiotic stresses such as drought, heat, osmotic, salt and irradiation. Also, we summarize findings from recent publications looking for a connection between these processes and their possible client(s) proteins. From this, we observed that a clear connection has been established between the ERAD and UPR mechanisms, but evidence that connects ERQC components to these both processes or their possible client(s) proteins is still lacking. As a proposal, we suggest the use of proteomics approaches to uncover the identity of these proteins and their connection with ER proteostasis.

Genome-wide identification and characterization of Solanum tuberosum BiP genes reveal the role of the promoter architecture in BiP gene diversity

The endoplasmic reticulum (ER) immunoglobulin binding proteins (BiPs) are molecular chaperones involved in normal protein maturation and refolding malformed proteins through the unfolded protein response (UPR). Plant BiPs belong to a multi-gene family contributing to development, immunity, and responses to environmental stresses. This study identified three BiP homologs in the Solanum tuberosum (potato) genome using phylogenetic, amino acid sequence, 3-D protein modeling, and gene structure analysis. These analyses revealed that StBiP1 and StBiP2 grouped with AtBiP2, whereas StBiP3 grouped with AtBiP3. While the protein sequences and folding structures are highly similar, these StBiPs are distinguishable by their expression patterns in different tissues and in response to environmental stressors such as treatment with heat, chemicals, or virus elicitors of UPR. Ab initio promoter analysis revealed that potato and Arabidopsis BiP1 and BiP2 promoters were highly enriched with cis-regulatory elements (CREs) linked to developmental processes, whereas BiP3 promoters were enriched with stress related CREs. The frequency and linear distribution of these CREs produced two phylogenetic branches that further resolve the groups identified through gene phylogeny and exon/intron phase analysis. These data reveal that the CRE architecture of BiP promoters potentially define their spatio-temporal expression patterns under developmental and stress related cues.

Genome-wide identification and characterization of Solanum tuberosum BiP genes reveal the role of the promoter architecture in BiP gene diversity

The endoplasmic reticulum (ER) immunoglobulin binding proteins (BiPs) are molecular chaperones involved in normal protein maturation and refolding malformed proteins through the unfolded protein response (UPR). Plant BiPs belong to a multi-gene family contributing to development, immunity, and responses to environmental stresses. This study identified three BiP homologs in the Solanum tuberosum (potato) genome using phylogenetic, amino acid sequence, 3-D protein modeling, and gene structure analysis. These analyses revealed that StBiP1 and StBiP2 grouped with AtBiP2, whereas StBiP3 grouped with AtBiP3. While the protein sequences and folding structures are highly similar, these StBiPs are distinguishable by their expression patterns in different tissues and in response to environmental stressors such as treatment with heat, chemicals, or virus elicitors of UPR. Ab initio promoter analysis revealed that potato and Arabidopsis BiP1 and BiP2 promoters were highly enriched with cis-regulatory elements (CREs) linked to developmental processes, whereas BiP3 promoters were enriched with stress related CREs. The frequency and linear distribution of these CREs produced two phylogenetic branches that further resolve the groups identified through gene phylogeny and exon/intron phase analysis. These data reveal that the CRE architecture of BiP promoters potentially define their spatio-temporal expression patterns under developmental and stress related cues.

Cellular alteration and differential protein profile explain effects of GA3 and ABA and their inhibitor on Trichocline catharinensis (Asteraceae) seed germination

Seed physiology of wild species has not been studied as deeply as that of domesticated crop species. Trichocline catharinensis (Asteraceae) is an endemic wildflower species from the high-altitude fields of southern Brazil. This species is of interest as a source of genes to improve cultivated Asteraceae because of its ornamental features, disease resistance and ability to tolerate drought and poor soil conditions. We studied the effects of abscisic acid (ABA) and gibberellic acid (GA₃ ) and their inhibitors, fluridone (FLU) and paclobutrazol (PAC), on seed germination. We individually assessed ultrastructural changes and differential protein accumulation. The principal component analysis explained 69.66% of differential accumulation for 32 proteins at phase II of seed germination in response to hormone and inhibitor treatment. GA₃ -imbibed seed germination (98.75%) resulted in increased protein accumulation to meet energy demand, redox regulation, and reserve metabolism activation. FLU-imbibed seeds showed a higher germination speed index as a consequence of metabolism activation. ABA-imbibed seeds (58.75%) showed osmotolerance and flattened cells in the hypocotyl-radicular axis, suggesting that ABA inhibits cell expansion. PAC-imbibed seeds remained at phase II for 300 h, and germination was suppressed (7.5%) because of the increased signaling proteins and halted reserve mobilization. Therefore, our findings provide insight into the behavior of Asteraceae non-dormant seed germination, which broadens our knowledge of seed germination in a wild and endemic plant species from a threatened ecosystem.

Wheat grain protein accumulation and polymerization mechanisms driven by nitrogen fertilization

In wheat (Triticum aestivum) grain yield and grain protein content are negatively correlated, making the simultaneous increase of the two traits challenging. Apart from genetic approaches, modification of nitrogen fertilization offers a feasible option to achieve this aim. In this study, a range of traits related to nitrogen-use efficiency in six Australian bread wheat varieties were investigated under different nitrogen treatments using 3-year multisite field trials. Changes in the individual storage protein composition were detected by high-performance liquid chromatography. Our results indicated that wheat grain yield and grain protein content reacted similarly to nitrogen availability, with grain yield being slightly more sensitive than grain protein content, and that genotype is a vital determinant of grain protein yield. Measurement of the glutamine synthetase activity of flag leaves and developing grains revealed that high nitrogen availability prompted the participation of glutamine in biological processes. In addition, a more significant accumulation of gluten macropolymer was observed under the high-nitrogen treatment from 21 days post-anthesis, and the underlying mechanism was elucidated by a comparative proteomics study. A yeast two-hybrid experiment confirmed this mechanism. The results of this study revealed that peptidyl-prolyl cis-trans isomerase (PPIase) was SUMOylated with the assistance of small ubiquitin-related modifier 1 and that high nitrogen availability facilitated this connection for the subsequent protein polymerization. Additionally, luminal-binding protein 2 in the endoplasmic reticulum played a similar role to PPIase in the aggregation of protein under high-nitrogen conditions.

Morpho-physiological and proteomic responses of Aegilops tauschii to imposed moisture stress

Moisture stress is the most important limitation of wheat production in the worldwide. Among the tribe Triticeae, Aegilops tauschii is one of the most valuable gene sources of resistance to abiotic stresses. In order to identify the most tolerant accession to moisture stress, and to understand its adaptive mechanisms at the molecular level, the present experiment was carried out on ten Ae. tauschii accessions under normal (95% soil pot capacity) and moisture stress (45% soil pot capacity) conditions. At the start of the heading time, the expanded flag leaves of treated and untreated plants were sampled for two-dimensional electrophoresis (2-DE) based on proteomics approach. A19 accession was less affected by the imposed moisture stress; therefore, it was used for the proteomics experiment. Among 252 protein spots which were reproducibly detected in each given 2-DE gels, 25 spots showed significant differences between the two moisture treatments; 17 spots were upregulated and 8 spots were downregulated. The identified proteins by MALDI-TOF/TOF, were allocated to seven functional protein groups, which were mainly involved in photosynthesis/respiration (28.5%), carbohydrate metabolism (14.2%), energy metabolism (7.1%), chaperone (14.2%), protein translation and processing (14.2%), repair and stability of the genome (7.1%) and unknown function (14.2%). We report this for the first time that RMI2 protein (in the group of repair and stability of the genome) was significantly changed in wheat in response to moisture stress. We believe that, the identified proteins could play important roles in acclimation and tolerance to moisture stress and provide the genetic pathways for improving tolerance to moisture stress in wheat.

Mechanisms of wheat (Triticum aestivum) grain storage proteins in response to nitrogen application and its impacts on processing quality

Basis for the effects of nitrogen (N) on wheat grain storage proteins (GSPs) and on the establishment of processing quality are far from clear. The response of GSPs and processing quality parameters to four N levels of four common wheat cultivars were investigated at two sites over two growing seasons. Except gluten index (GI), processing quality parameters as well as GSPs quantities were remarkably improved by increasing N level. N level explained 4.2~59.2% and 10.4~80.0% variability in GSPs fractions and processing quality parameters, respectively. The amount of N remobilized from vegetative organs except spike was significantly increased when enhancing N application. GSPs fractions and processing quality parameters except GI were only highly and positively correlated with the amount of N remobilized from stem with sheath. N reassimilation in grain was remarkably strengthened by the elevated activity and expression level of glutamine synthetase. Transcriptome analysis showed the molecular mechanism of seeds in response to N levels during 10~35 days post anthesis. Collectively, we provided comprehensive understanding of N-responding mechanisms with respect to wheat processing quality from N source to GSPs biosynthesis at the agronomic, physiological and molecular levels, and screened candidate genes for quality breeding.

Transcriptional regulation of osmotic stress tolerance in wheat (Triticum aestivum L.)

The current review provides an updated, new insights into the regulation of transcription mediated underlying mechanisms of wheat plants to osmotic stress perturbations. Osmotic stress tolerance mechanisms being complex are governed by multiple factors at physiological, biochemical and at the molecular level, hence approaches like "OMICS" that can underpin mechanisms behind osmotic tolerance in wheat is of paramount importance. The transcription factors (TFs) are a class of molecular proteins, which are involved in regulation, modulation and orchestrating the responses of plants to a variety of environmental stresses. Recent reports have provided novel insights on the role of TFs in osmotic stress tolerance via direct molecular links. However, our knowledge on the regulatory role TFs during osmotic stress tolerance in wheat remains limited. The present review in its first part sheds light on the importance of studying the role of osmotic stress tolerance in wheat plants and second aims to decipher molecular mechanisms of TFs belonging to several classes, including DREB, NAC, MYB, WRKY and bHLH, which have been reported to engage in osmotic stress mediated gene expression in wheat and third part covers the systems biology approaches to understand the transcriptional regulation of osmotic stress and the role of long non-coding RNAs in response to osmotic stress with special emphasis on wheat. The current concept may lead to an understanding in molecular regulation and signalling interaction of TFs under osmotic stress to clarify challenges and problems for devising potential strategies to improve complex regulatory events involved in plant tolerance to osmotic stress adaptive pathways in wheat.

Wheat differential gene expression induced by different races of Puccinia triticina

Puccinia triticina, the causal agent of wheat leaf rust, causes significant losses in wheat yield and quality each year worldwide. During leaf rust infection, the host plant recognizes numerous molecules, some of which trigger host defenses. Although P. triticina reproduces clonally, there is still variation within the population due to a high mutation frequency, host specificity, and environmental adaptation. This study explores how wheat responds on a gene expression level to different P. triticina races. Six P. triticina races were inoculated onto a susceptible wheat variety and samples were taken at six days post inoculation, just prior to pustule eruption. RNA sequence data identified 63 wheat genes differentially expressed between the six races. A time course, conducted over the first seven days post inoculation, was used to examine the expression pattern of 63 genes during infection. Forty-seven wheat genes were verified to have differential expression. Three common expression patterns were identified. In addition, two genes were associated with race specific gene expression. Differential expression of an ER molecular chaperone gene was associated with races from two different P. triticina lineages. Also, differential expression in an alanine glyoxylate aminotransferase gene was associated with races with virulence shifts for leaf rust resistance genes.

Osmotic Stress Induced Cell Death in Wheat Is Alleviated by Tauroursodeoxycholic Acid and Involves Endoplasmic Reticulum Stress-Related Gene Expression

Although, tauroursodeoxycholic acid (TUDCA) has been widely studied in mammalian cells because of its role in inhibiting apoptosis, its effects on plants remain almost unknown, especially in the case of crops such as wheat. In this study, we conducted a series of experiments to explore the effects and mechanisms of action of TUDCA on wheat growth and cell death induced by osmotic stress. Our results show that TUDCA: (1) ameliorates the impact of osmotic stress on wheat height, fresh weight, and water content; (2) alleviates the decrease in chlorophyll content as well as membrane damage caused by osmotic stress; (3) decreases the accumulation of reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes under osmotic stress; and (4) to some extent alleviates osmotic stress-induced cell death probably by regulating endoplasmic reticulum (ER) stress-related gene expression, for example expression of the basic leucine zipper genes bZIP60B and bZIP60D, the binding proteins BiP1 and BiP2, the protein disulfide isomerase PDIL8-1, and the glucose-regulated protein GRP94. We also propose a model that illustrates how TUDCA alleviates osmotic stress-related wheat cell death, which provides an important theoretical basis for improving plant stress adaptation and elucidates the mechanisms of ER stress-related plant osmotic stress resistance.

Characterization of BiP Genes from Pepper (Capsicum annuum L.) and the Role of CaBiP1 in Response to Endoplasmic Reticulum and Multiple Abiotic Stresses

Adverse environmental conditions have a detrimental impact on crop growth and development, and cause protein denaturation or misfolding. The binding protein (BiP) plays an important protective role by alleviating endoplasmic reticulum (ER) stress induced by misfolded proteins. In this study, we characterized three BiP genes (CaBiP1, CaBiP2, and CaBiP3) in pepper, an economically important vegetable and spice species. The role of CaBiP1 in plant tolerance to ER stress and adverse environmental conditions (including heat, salinity, osmotic and drought stress) were investigated. All the expected functional and signaling domains were detected in three BiP proteins, but the motifs and exon-intron distribution differed slightly in CaBiP3. CaBiP1 and CaBiP2 were constitutively expressed in all the tested tissues under both normal and stressed conditions, whereas CaBiP3 was mainly expressed following stress. Silencing of CaBiP1 reduced pepper tolerance to ER stress and various environment stresses, and was accompanied by increased H₂O₂ accumulation, MDA content, relative electric leakage (REL), water loss rate, and a reduction in soluble protein content and relative water content (RWC) in the leaves. Conversely, overexpression of CaBiP1 in Arabidopsis enhanced tolerance to ER stress and multiple environment stresses, as demonstrated by an increase in germination rate, root length, survival rate, RWC, the unfolded protein response (UPR) pathway, and a decrease in water loss rate. Our results suggest that CaBiP1 may contribute to plant tolerance to abiotic stresses by reducing ROS accumulation, increasing the water-retention ability, and stimulating UPR pathways and expression of stress-related genes.

Analysis of the embryo proteome of sycamore (Acer pseudoplatanus L.) seeds reveals a distinct class of proteins regulating dormancy release

Acer pseudoplatanus seeds are characterized by a deep physiological embryo dormancy that requires a few weeks of cold stratification in order to promote germination. Understanding the function of proteins and their related metabolic pathways, in conjunction with the plant hormones implicated in the breaking of seed dormancy, would expand our knowledge pertaining to this process. In this study, a proteomic approach was used to analyze the changes occurring in seeds in response to cold stratification, which leads to dormancy release. In addition, the involvement of abscisic (ABA) and gibberellic acids (GA) was also examined. Fifty-three proteins showing significant changes were identified by mass spectrometry. An effect of ABA on protein variation was observed at the beginning of stratification, while the influence of GA on protein abundance was observed during the middle phase of stratification. The majority of proteins associated with dormancy breaking in the presence of only water, and also ABA or GA, were classified as being involved in metabolism and genetic information processing. For metabolic-related proteins, the effect of ABA on protein abundance was stimulatory for half of the proteins and inhibitory for half of the proteins. On the other hand, the effect on genetic information processing related proteins was stimulatory. GA was found to upregulate both metabolic-related and genetic information processing-related proteins. While seed dormancy breaking depends on proteins involved in a variety of processes, proteins associated with methionine metabolism (adenosine kinase, methionine synthase) and glycine-rich RNA binding proteins appear to be of particular importance.

LcBiP, a endoplasmic reticulum chaperone binding protein gene from Lycium chinense, confers cadmium tolerance in transgenic tobacco

Cadmium (Cd) accumulation is very toxic to plants. The presence of Cd may lead to excessive production of reactive oxygen species (ROS), and then cause inhibition of plant growth. The endoplasmic reticulum chaperone binding protein (BiP) is an important functional protein, which has been shown to function as a sensor of alterations in the ER environment. BiP overexpression in plants was shown to increase drought tolerance through inhibition of ROS accumulation. Due to the above relationships, it is likely that there may be a link between Cd stress tolerance, ROS accumulation and the BiP transcript expression in plants. In this study, a BiP gene, LcBiP, from L. chinense was isolated and characterized. Overexpression of LcBiP in tobacco conferred Cd tolerance. Under Cd stress conditions, the transgenic tobacco lines exhibited better chlorophyll retention, less accumulation of ROS, longer root length, more glutathione (GSH) content, and less antioxidant enzyme activity than the wild type. These data demonstrated that LcBiP act as a positive regulator in Cd stress tolerance. It is hypothesized that the improved Cd tolerance of the transgenic tobacco plants may be due to the enhanced ROS scavenging capacity. The enhancement of GSH content might contribute to this ROS scavenging capacity in the transgenic plants. However, the underlying mechanism for BiP-mediated increase in Cd stress tolerance need to be further clarified.