Calcium-regulated proteolysis of eEF1A

The elongation factor 1-alpha as storage reserve and environmental sensor in Nicotiana tabacum L. seeds

Given their critical role in plant reproduction and survival, seeds demand meticulous regulatory mechanisms to effectively store and mobilize reserves. Within seeds, the condition of storage reserves heavily depends on environmental stimuli and hormonal activation. Unlike non-protein reserves that commonly employ dedicated regulatory proteins for signaling, proteinaceous reserves may show a unique form of 'self-regulation', amplifying efficiency and precision in this process. Proteins rely on stability to carry out their functions. However, in specific physiological contexts, particularly in seed germination, protein instability becomes essential, fulfilling roles from signaling to regulation. In this study, the elongation factor 1-alpha has been identified as a main proteinaceous reserve in Nicotiana tabacum L. seeds and showed peculiar changes in stability based on tested chemical and physical conditions. A detailed biochemical analysis followed these steps to enhance our understanding of these protein attributes. The protein varied its behavior under different conditions of pH, temperature, and salt concentration, exhibiting shifts within physiological ranges. Notably, distinct solubility transitions were observed, with the elongation factor 1-alpha becoming insoluble upon reaching specific thresholds determined by the tested chemical and physical conditions. The findings are discussed within the context of seed signaling in response to environmental conditions during the key transitions of dormancy and germination.

Immunogens in Balamuthia mandrillaris: a proteomic exploration

Balamuthia mandrillaris is the causative agent of granulomatous amoebic encephalitis, a rare and often fatal infection affecting the central nervous system. The amoeba is isolated from diverse environmental sources and can cause severe infections in both immunocompromised and immunocompetent individuals. Given the limited understanding of B. mandrillaris, our research aimed to explore its protein profile, identifying potential immunogens crucial for early granulomatous amoebic encephalitis diagnosis. Cultures of B. mandrillaris and other amoebas were grown under axenic conditions, and total amoebic extracts were obtained. Proteomic analyses, including two-dimensional electrophoresis and mass spectrometry, were performed. A 50-kDa band showed a robust recognition of antibodies from immunized BALB/c mice; peptides contained in this band were matched with elongation factor-1 alpha, which emerged as a putative key immunogen. Besides, lectin blotting revealed the presence of glycoproteins in B. mandrillaris, and confocal microscopy demonstrated the focal distribution of the 50-kDa band throughout trophozoites. Cumulatively, these observations suggest the participation of the 50-kDa band in adhesion and recognition mechanisms. Thus, these collective findings demonstrate some protein characteristics of B. mandrillaris, opening avenues for understanding its pathogenicity and developing diagnostic and therapeutic strategies.

Interaction of negative regulator OsWD40-193 with OseEF1A1 inhibits Oryza sativa resistance to Hirschmanniella mucronata infection

Rice is a crucial food crop worldwide, but it is highly susceptible to Hirschmanniella mucronata, a migratory parasitic nematode. No rice variety has been identified that could resist H. mucronata infection. Therefore, it is very important to study the interaction between rice and H. mucronata to breed resistant rice varieties. Here, we demonstrated that protein OsWD40-193 interacted with the extension factor OseEF1A1 and both were negative regulators inhibiting rice resistance to H. mucronata infection. Overexpression of either OsWD40-193 or OseEF1A1 led to enhance susceptibility to H. mucronata, whereas the absence of OsWD40-193 or OseEF1A1 led to resistance. Further transcriptomic analysis showed that OseEF1A1 deletion altered the expression of genes association with salicylic acid, jasmonic acid and abolic acid signaling pathways and increased the accumulation of secondary metabolites to enhance resistance in rice. Our study showed that H. mucronata infection affected the expression of negative regulators in rice and inhibited rice resistance, which was conducive to the infection of nematode. Together, our data showed that H. mucronata affected the expression of negative regulators to facilitate its infection and provided potential target genes to engineering resistance germplasm via gene editing of the negative regulators.

Overexpression of the elongation factor MtEF1A1 promotes salt stress tolerance in Arabidopsis thaliana and Medicago truncatula

BACKGROUND

Elongation factor 1 A (EF1A), an essential regulator for protein synthesis, has been reported to participate in abiotic stress responses and environmental adaption in plants. However, the role of EF1A in abiotic stress response was barely studied in Medicago truncatula. Here, we identified elongation factor (EF) genes of M. truncatula and studied the salt stress response function of MtEF1A1 (MTR_6g021805).

RESULTS

A total of 34 EF genes were identified in the M. truncatula genome. Protein domains and motifs of EFs were highly conserved in plants. MtEF1A1 has the highest expression levels in root nodules and roots, followed by the leaves and stems. Transgenic Arabidopsis thaliana overexpressing MtEF1A1 was more resistant to salt stress treatment, with higher germination rate, longer roots, and more lateral roots than wild type plant. In addition, lower levels of H₂O₂ and malondialdehyde (MDA) were also detected in transgenic Arabidopsis. Similarly, MtEF1A1 overexpressing M. truncatula was more resistant to salt stress and had lower levels of reactive oxygen species (ROS) in leaves. Furthermore, the expression levels of abiotic stress-responsive genes (MtRD22A and MtCOR15A) and calcium-binding genes (MtCaM and MtCBL4) were upregulated in MtEF1A1 overexpressing lines of M. truncatula.

CONCLUSION

These results suggested that MtEF1A1 play a positive role in salt stress regulation. MtEF1A1 may realize its function by binding to calmodulin (CaM) or by participating in Ca²⁺-dependent signaling pathway. This study revealed that MtEF1A1 is an important regulator for salt stress response in M. truncatula, and provided potential strategy for salt-tolerant plant breeding.

Calcium signaling contributes to xylem vessel cell differentiation via post-transcriptional regulation of VND7 downstream events

Secondary cell walls (SCWs) accumulate in specific cell types of vascular plants, notably xylem vessel cells. Previous work has shown that calcium ions (Ca²⁺) participate in xylem vessel cell differentiation, but whether they function in SCW deposition remains unclear. In this study, we examined the role of Ca²⁺ in SCW deposition during xylem vessel cell differentiation using Arabidopsis thaliana suspension-cultured cells carrying the VND7-inducible system, in which VND7 activity can be post-translationally upregulated to induce transdifferentiation into protoxylem-type vessel cells. We observed that extracellular Ca²⁺ concentration was a crucial determinant of differentiation, although it did not have consistent effects on the transcription of VND7-downstream genes as a whole. Increasing the Ca²⁺ concentration reduced differentiation but the cells could generate the spiral patterning of SCWs. Exposure to a calcium-channel inhibitor partly restored differentiation but resulted in abnormal branched and net-like SCW patterning. These data suggest that Ca²⁺ signaling participates in xylem vessel cell differentiation via post-transcriptional regulation of VND7-downstream events, such as patterning of SCW deposition.

LreEF1A4, a Translation Elongation Factor from Lilium regale, Is Pivotal for Cucumber Mosaic Virus and Tobacco Rattle Virus Infections and Tolerance to Salt and Drought

Eukaryotic translation elongation factors are implicated in protein synthesis across different living organisms, but their biological functions in the pathogenesis of cucumber mosaic virus (CMV) and tobacco rattle virus (TRV) infections are poorly understood. Here, we isolated and characterized a cDNA clone, LreEF1A4, encoding the alpha subunit of elongation factor 1, from a CMV-elicited suppression subtractive hybridization library of Lilium regale. The infection tests using CMV remarkably increased transcript abundance of LreEF1A4; however, it also led to inconsistent expression profiles of three other LreEF1A homologs (LreEF1A1-3). Protein modelling analysis revealed that the amino acid substitutions among four LreEF1As may not affect their enzymatic functions. LreEF1A4 was ectopically overexpressed in petunia (Petunia hybrida), and transgenic plants exhibited delayed leaf and flower senescence, concomitant with increased transcription of photosynthesis-related genes and reduced expression of senescence-associated genes, respectively. A compromised resistance to CMV and TRV infections was found in transgenic petunia plants overexpressing LreEF1A4, whereas its overexpression resulted in an enhanced tolerance to salt and drought stresses. Taken together, our data demonstrate that LreEF1A4 functions as a positive regulator in viral multiplication and plant adaption to high salinity and dehydration.

Phylogenetic analysis and differential expression of EF1α genes in soybean during development, stress and phytohormone treatments

The EF1α is a multifunctional protein with additional unrelated activities to its primary function in translation. This protein is encoded by a multigene family and few studies are still available in plants. Expression of six EF1α genes in Glycine max was performed using RT-qPCR and RNA-seq data to advance in the function of each gene during plant development, stress conditions and phytohormone treatments. A phylogenetic classification in Phaseoleae tribe was used to identify the G. max EF1α genes (EF1α 1a1, 1a2, 1b, 2a, 2b and 3). Three EF1α types (1-3) were found in Phaseoleae revealing duplications in G. max types 1 and 2. EF1α genes were expressed in all studied tissues, however, specific amount of each transcript was detected. In plant development, all EF1α transcripts were generally more expressed in younger tissues, however, in unifoliolate leaves and cotyledons a higher expression occurred in older tissues. Five EF1α genes (except 2a) were up-regulated under stress in a response tissue/stress/cultivar-dependent. EF1α 3 was the most stress-induced gene linked to cultivar stress tolerance mainly in aerial tissues. Auxin, salicylate and ethylene induced differentially the EF1α expression. Overall, this study provides a consistent EF1α classification in Phaseoleae tribe to better understand their functional evolution. The RT-qPCR and RNA-seq EF1α expression profiles were consistent, both exhibiting expression diversification of each gene (spatio-temporal, stress and phytohormone stimuli). Our results point out the EF1α genes, especially EF1α 3, as candidate for developing a useful tool for future G. max breeding.

Effect of proteasome inhibitor clasto-lactacystin-beta-lactone on the proteome of the haloarchaeon Haloferax volcanii

Proteasomes play key roles in a variety of eukaryotic cell functions, including translation, transcription, metabolism, DNA repair and cell-cycle control. The biological functions of these multicatalytic proteases in archaea, however, are poorly understood. In this study, Haloferax volcanii was used as a model to determine the influence the proteasome-specific inhibitor clasto-lactacystin-beta-lactone (cLbetaL) has on archaeal proteome composition. Addition of 20-30 microM cLbetaL had a widespread effect on the proteome, with a 38-42 % increase in the number of 2-D gel electrophoresis (2-DE) protein spots, from an average of 627 to 1036 spots. Protein identities for 17 of the spots that were easily separated by 2-DE and unique and/or increased 2- to 14-fold in the cLbetaL-treated cells were determined by tandem mass spectrometry (MS/MS). These included protein homologues of the DJ-1/ThiJ family, mobilization of sulfur system, translation elongation factor EF-1 A, ribosomal proteins, tubulin-like FtsZ, divalent metal ABC transporter, dihydroxyacetone kinase DhaL, aldehyde dehydrogenase and 2-oxoacid decarboxylase E1beta. Based on these results, inhibition of H. volcanii proteasomes had a global influence on proteome composition, including proteins involved in central functions of the cell.

Molecular characterization and expression analysis of nine cotton GhEF1A genes encoding translation elongation factor 1A

The translation elongation factor 1A, eEF1A, plays an important role in protein synthesis, catalyzing the binding of aminoacyl-tRNA to the A-site of the ribosome by a GTP-dependent mechanism. To investigate the role of eEF1A for protein synthesis in cotton fiber development, nine different cDNA clones encoding eukaryotic translation elongation factor 1A were isolated from cotton (Gossypium hirsutum) fiber cDNA libraries. The isolated genes (cDNAs) were designated cotton elongation factor 1A gene GhEF1A1, GhEF1A2, GhEF1A3, GhEF1A4, GhEF1A5, GhEF1A6, GhEF1A7, GhEF1A8, GhEF1A9, respectively. They share high sequence homology at nucleotide level (71-99% identity) in the coding region and at amino acid level (96-99% identity) among each other. Phylogenetic analysis demonstrated that the nine GhEF1A genes can be divided into 5-6 subfamilies, indicating the divergence occurred in structures of the genes as well as the deduced proteins during evolution. Real-time quantitative RT-PCR analysis revealed that GhEF1A genes are differentially expressed in different tissues/organs. Of the nine GhEF1A genes, five are expressed at relatively high levels in young fibers. Further analysis indicated that expressions of the GhEF1As in fiber are highly developmental-regulated, suggesting that protein biosynthesis is very active at the early fiber elongation.

Calcium oscillations in higher plants

There is considerable interest in the possibility that stimulus-induced oscillations in cytosolic free calcium encode information that is used to specify the outcome of the final response in calcium-based signalling pathways in plants. Recent results provide conclusive evidence that plant cells can decipher complex calcium signatures.

A 90-kD phospholipase D from tobacco binds to microtubules and the plasma membrane

The organization of microtubule arrays in the plant cell cortex involves interactions with the plasma membrane, presumably through protein bridges. We have used immunochemistry and monoclonal antibody 6G5 against a candidate bridge protein, a 90-kD tubulin binding protein (p90) from tobacco BY-2 membranes, to characterize the protein and isolate the corresponding gene. Screening an Arabidopsis cDNA expression library with the antibody 6G5 produced a partial clone encoding phospholipase D (PLD), and a full-length gene was obtained by sequencing a corresponding expressed sequence tag clone. The predicted protein of 857 amino acids contains the active sites of a phospholipid-metabolizing enzyme and a Ca(2+)-dependent lipid binding domain and is identical to Arabidopsis PLD delta. Two amino acid sequences obtained by Edman degradation of the tobacco p90 are identical to corresponding segments of a PLD sequence from tobacco. Moreover, immunoprecipitation using the antibody 6G5 and tobacco BY-2 protein extracts gave significant PLD activity, and PLD activity of tobacco BY-2 membrane proteins was enriched 6.7-fold by tubulin-affinity chromatography. In a cosedimentation assay, p90 bound and decorated microtubules. In immunofluorescence microscopy of intact tobacco BY-2 cells or lysed protoplasts, p90 colocalized with cortical microtubules, and taxol-induced microtubule bundling was accompanied by corresponding reorganization of p90. Labeling of p90 remained along the plasma membrane when microtubules were depolymerized, although detergent extraction abolished the labeling. Therefore, p90 is a specialized PLD that associates with membranes and microtubules, possibly conveying hormonal and environmental signals to the microtubule cytoskeleton.

A 90-kD phospholipase D from tobacco binds to microtubules and the plasma membrane

The organization of microtubule arrays in the plant cell cortex involves interactions with the plasma membrane, presumably through protein bridges. We have used immunochemistry and monoclonal antibody 6G5 against a candidate bridge protein, a 90-kD tubulin binding protein (p90) from tobacco BY-2 membranes, to characterize the protein and isolate the corresponding gene. Screening an Arabidopsis cDNA expression library with the antibody 6G5 produced a partial clone encoding phospholipase D (PLD), and a full-length gene was obtained by sequencing a corresponding expressed sequence tag clone. The predicted protein of 857 amino acids contains the active sites of a phospholipid-metabolizing enzyme and a Ca(2+)-dependent lipid binding domain and is identical to Arabidopsis PLD delta. Two amino acid sequences obtained by Edman degradation of the tobacco p90 are identical to corresponding segments of a PLD sequence from tobacco. Moreover, immunoprecipitation using the antibody 6G5 and tobacco BY-2 protein extracts gave significant PLD activity, and PLD activity of tobacco BY-2 membrane proteins was enriched 6.7-fold by tubulin-affinity chromatography. In a cosedimentation assay, p90 bound and decorated microtubules. In immunofluorescence microscopy of intact tobacco BY-2 cells or lysed protoplasts, p90 colocalized with cortical microtubules, and taxol-induced microtubule bundling was accompanied by corresponding reorganization of p90. Labeling of p90 remained along the plasma membrane when microtubules were depolymerized, although detergent extraction abolished the labeling. Therefore, p90 is a specialized PLD that associates with membranes and microtubules, possibly conveying hormonal and environmental signals to the microtubule cytoskeleton.

A 90-kD phospholipase D from tobacco binds to microtubules and the plasma membrane

The organization of microtubule arrays in the plant cell cortex involves interactions with the plasma membrane, presumably through protein bridges. We have used immunochemistry and monoclonal antibody 6G5 against a candidate bridge protein, a 90-kD tubulin binding protein (p90) from tobacco BY-2 membranes, to characterize the protein and isolate the corresponding gene. Screening an Arabidopsis cDNA expression library with the antibody 6G5 produced a partial clone encoding phospholipase D (PLD), and a full-length gene was obtained by sequencing a corresponding expressed sequence tag clone. The predicted protein of 857 amino acids contains the active sites of a phospholipid-metabolizing enzyme and a Ca(2+)-dependent lipid binding domain and is identical to Arabidopsis PLD delta. Two amino acid sequences obtained by Edman degradation of the tobacco p90 are identical to corresponding segments of a PLD sequence from tobacco. Moreover, immunoprecipitation using the antibody 6G5 and tobacco BY-2 protein extracts gave significant PLD activity, and PLD activity of tobacco BY-2 membrane proteins was enriched 6.7-fold by tubulin-affinity chromatography. In a cosedimentation assay, p90 bound and decorated microtubules. In immunofluorescence microscopy of intact tobacco BY-2 cells or lysed protoplasts, p90 colocalized with cortical microtubules, and taxol-induced microtubule bundling was accompanied by corresponding reorganization of p90. Labeling of p90 remained along the plasma membrane when microtubules were depolymerized, although detergent extraction abolished the labeling. Therefore, p90 is a specialized PLD that associates with membranes and microtubules, possibly conveying hormonal and environmental signals to the microtubule cytoskeleton.

PLANT PHOSPHOLIPASES

Phospholipases are a diverse series of enzymes that hydrolyze phospholipids. Multiple forms of phospholipases D, C, and A have been characterized in plants. These enzymes are involved in a broad range of functions in cellular regulation, lipid metabolism, and membrane remodeling. In recent years, increasing attention has been paid to the many roles of phospholipases in signal transduction. This review highlights recent developments in the understanding of biochemical, molecular biological, and functional aspects of various phospholipases in plants.