Functional characterization of selected LEA proteins from Arabidopsis thaliana in yeast and in vitro

Prokaryotic expression, purification, and the in vitro and in vivo protection study of dehydrin WDHN2 from Triticum aestivum

Dehydrins proteins accumulate and play important protective roles in most plants during abiotic stresses. The objective of this study was to characterize a YSK2-type dehydrin gene, WDHN2, isolated from Triticum aestivum previously. In this work, wheat dehydrin WDHN2 was expressed in Escherichia coli and purified by immobilized metal affinity chromatography, which exhibited as a single band by sodium dodecyl sulfonate polyacrylamide gel electrophoresis and western blotting. We show that WDHN2 is capable of alleviating lactate dehydrogenase inactivation from heat and desiccation in vitro enzyme activity protection assay. In vivo assay of Escherichia coli viability demonstrates the enhancement of cell survival by the overexpression of WDHN2. The protein aggregation prevention assay explores that WDHN2 has a broad protective effect on the cellular proteome. The results show that WDHN2 is mainly accumulated in the nucleus and cytosol, suggesting that this dehydrin may exert its function in both cellular compartments. Our data suggest that WDHN2 acts as a chaperone molecular in vivo.

Protective roles of highly conserved motif 1 in tardigrade cytosolic-abundant heat soluble protein in extreme environments

Tardigrades are remarkable microscopic animals that survive harsh conditions such as desiccation and extreme temperatures. Tardigrade-specific intrinsically disordered proteins (TDPs) play an essential role in the survival of tardigrades in extreme environments. Cytosolic-abundant heat soluble (CAHS) protein, a key TDP, is known to increase desiccation tolerance and to protect the activity of several enzymes under dehydrated conditions. However, the function and properties of each CAHS domain have not yet been elucidated in detail. Here, we aimed to elucidate the protective role of highly conserved motif 1 of CAHS in extreme environmental conditions. To examine CAHS domains, three protein constructs, CAHS Full (1-229), CAHS ∆Core (1-120_184-229), and CAHS Core (121-183), were engineered. The highly conserved CAHS motif 1 (124-142) in the CAHS Core formed an amphiphilic α helix, reducing the aggregate formation and protecting lactate dehydrogenase activity during dehydration-rehydration and freeze-thaw treatments, indicating that CAHS motif 1 in the CAHS Core was essential for maintaining protein solubility and stability. Aggregation assays and confocal microscopy revealed that the intrinsically disordered N- and C-terminal domains were more prone to aggregation under our experimental conditions. By explicating the functions of each domain in CAHS, our study proposes the possibility of using engineered proteins or peptides derived from CAHS as a potential candidate for biological applications in extreme environmental stress responses.

Design of functional intrinsically disordered proteins

Many proteins do not fold into a fixed three-dimensional structure, but rather function in a highly disordered state. These intrinsically disordered proteins pose a unique challenge to protein engineering and design: How can proteins be designed de novo if not by tailoring their structure? Here, we will review the nascent field of design of intrinsically disordered proteins with focus on applications in biotechnology and medicine. The design goals should not necessarily be the same as for de novo design of folded proteins as disordered proteins have unique functional strengths and limitations. We focus on functions where intrinsically disordered proteins are uniquely suited including disordered linkers, desiccation chaperones, sensors of the chemical environment, delivery of pharmaceuticals, and constituents of biomolecular condensates. Design of functional intrinsically disordered proteins relies on a combination of computational tools and heuristics gleaned from sequence-function studies. There are few cases where intrinsically disordered proteins have made it into industrial applications. However, we argue that disordered proteins can perform many roles currently performed by organic polymers, and that these proteins might be more designable due to their modularity.

Protein Disorder in Plant Stress Adaptation: From Late Embryogenesis Abundant to Other Intrinsically Disordered Proteins

Global climate change has caused severe abiotic and biotic stresses, affecting plant growth and food security. The mechanical understanding of plant stress responses is critical for achieving sustainable agriculture. Intrinsically disordered proteins (IDPs) are a group of proteins without unique three-dimensional structures. The environmental sensitivity and structural flexibility of IDPs contribute to the growth and developmental plasticity for sessile plants to deal with environmental challenges. This article discusses the roles of various disordered proteins in plant stress tolerance and resistance, describes the current mechanistic insights into unstructured proteins such as the disorder-to-order transition for adopting secondary structures to interact with specific partners (i.e., cellular membranes, membrane proteins, metal ions, and DNA), and elucidates the roles of liquid-liquid phase separation driven by protein disorder in stress responses. By comparing IDP studies in animal systems, this article provides conceptual principles of plant protein disorder in stress adaptation, reveals the current research gaps, and advises on the future research direction. The highlighting of relevant unanswered questions in plant protein disorder research aims to encourage more studies on these emerging topics to understand the mechanisms of action behind their stress resistance phenotypes.

Plants use molecular mechanisms mediated by biomolecular condensates to integrate environmental cues with development

This review highlights recent literature on biomolecular condensates in plant development and discusses challenges for fully dissecting their functional roles. Plant developmental biology has been inundated with descriptive examples of biomolecular condensate formation, but it is only recently that mechanistic understanding has been forthcoming. Here, we discuss recent examples of potential roles biomolecular condensates play at different stages of the plant life cycle. We group these examples based on putative molecular functions, including sequestering interacting components, enhancing dwell time, and interacting with cytoplasmic biophysical properties in response to environmental change. We explore how these mechanisms could modulate plant development in response to environmental inputs and discuss challenges and opportunities for further research into deciphering molecular mechanisms to better understand the diverse roles that biomolecular condensates exert on life.

Genome-wide identification and analysis of LEA_2 gene family in alfalfa (Medicago sativa L.) under aluminum stress

Late embryonic development abundant proteins (LEAs) are a large family of proteins commonly existing in plants. LEA_2 is the largest subfamily in the LEA, it plays an important role in plant resistance to abiotic stress. In order to explore the characteristics of LEA_2 gene family members in alfalfa (Medicago sativa L.), 155 members of LEA_2 (MsLEA_2) family were identified from alfalfa genome. Bioinformatics analysis was conducted from the aspects of phylogenetic relationship, chromosome distribution, chromosome colinearity, physical and chemical properties, motif composition, exon-intron structure, cis-element and so on. Expression profiles of MsLEA_2 gene were obtained based on Real-time fluorescent quantitative PCR (qRT-PCR) analysis and previous RNA-seq data under aluminum (Al) stress. Bioinformatics results were shown that the MsLEA_2 genes are distributed on all 32 chromosomes. Among them, 85 genes were present in the gene clusters, accounting for 54.83%, and chromosome Chr7.3 carries the largest number of MsLEA_2 (19 LEA_2 genes on Chr7.3). Chr7.3 has a unique structure of MsLEA_2 distribution, which reveals a possible special role of Chr7.3 in ensuring the function of MsLEA_2. Transcriptional structure analysis revealed that the number of exons in each gene varies from 1 to 3, and introns varies from 0 to 2. Cis-element analysis identified that the promoter region of MsLEA_2 is rich in ABRE, MBS, LTR, and MeJARE, indicating MsLEA_2 has stress resistance potential under abiotic stress. RNA-seq data and qRT-PCR analyses showed that most of the MsLEA_2 members were up-regulated when alfalfa exposed to Al stress. This study revealed that phylogenetic relationship and possible function of LEA_ 2 gene in alfalfa, which were helpful for the functional analysis of LEA_ 2 proteins in the future and provided a new theoretical basis for improving Al tolerance of alfalfa.

Genomic Analysis of LEA Genes in Carica papaya and Insight into Lineage-Specific Family Evolution in Brassicales

Late embryogenesis abundant (LEA) proteins comprise a diverse superfamily involved in plant development and stress responses. This study presents a first genome-wide analysis of LEA genes in papaya (Carica papaya L., Caricaceae), an economically important tree fruit crop widely cultivated in the tropics and subtropics. A total of 28 members were identified from the papaya genome, which belong to eight families with defined Pfam domains, i.e., LEA_1 (3), LEA_2 (4), LEA_3 (5), LEA_4 (5), LEA_5 (2), LEA_6 (2), DHN (4), and SMP (3). The family numbers are comparable to those present in Ricinus communis (Euphorbiaceae, 28) and Moringa oleifera (Moringaceae, 29), but relatively less than that found in Moringa oleifera (Cleomaceae, 39) and Arabidopsis thaliana (Brassicaceae, 51), implying lineage-specific evolution in Brassicales. Indeed, best-reciprocal-hit-based sequence comparison and synteny analysis revealed the presence of 29 orthogroups, and significant gene expansion in Tarenaya and Arabidopsis was mainly contributed by whole-genome duplications that occurred sometime after their split with the papaya. Though a role of transposed duplication was also observed, tandem duplication was shown to be a key contributor in gene expansion of most species examined. Further comparative analyses of exon-intron structures and protein motifs supported fast evolution of this special superfamily, especially in Arabidopsis. Transcriptional profiling revealed diverse expression patterns of CpLEA genes over various tissues and different stages of developmental fruit. Moreover, the transcript level of most genes appeared to be significantly regulated by drought, cold, and salt stresses, corresponding to the presence of cis-acting elements associated with stress response in their promoter regions. These findings not only improve our knowledge on lineage-specific family evolution in Brassicales, but also provide valuable information for further functional analysis of LEA genes in papaya.

Genome-wide identification, evolutionary and expression analyses of LEA gene family in peanut (Arachis hypogaea L.)

BACKGROUND

Late embryogenesis abundant (LEA) proteins are a group of highly hydrophilic glycine-rich proteins, which accumulate in the late stage of seed maturation and are associated with many abiotic stresses. However, few peanut LEA genes had been reported, and the research on the number, location, structure, molecular phylogeny and expression of AhLEAs was very limited.

RESULTS

In this study, 126 LEA genes were identified in the peanut genome through genome-wide analysis and were further divided into eight groups. Sequence analysis showed that most of the AhLEAs (85.7%) had no or only one intron. LEA genes were randomly distributed on 20 chromosomes. Compared with tandem duplication, segmental duplication played a more critical role in AhLEAs amplication, and 93 segmental duplication AhLEAs and 5 pairs of tandem duplication genes were identified. Synteny analysis showed that some AhLEAs genes come from a common ancestor, and genome rearrangement and translocation occurred among these genomes. Almost all promoters of LEAs contain ABRE, MYB recognition sites, MYC recognition sites, and ERE cis-acting elements, suggesting that the LEA genes were involved in stress response. Gene transcription analyses revealed that most of the LEAs were expressed in the late stages of peanut embryonic development. LEA3 (AH16G06810.1, AH06G03960.1), and Dehydrin (AH07G18700.1, AH17G19710.1) were highly expressed in roots, stems, leaves and flowers. Moreover, 100 AhLEAs were involved in response to drought, low-temperature, or Al stresses. Some LEAs that were regulated by different abiotic stresses were also regulated by hormones including ABA, brassinolide, ethylene and salicylic acid. Interestingly, AhLEAs that were up-regulated by ethylene and salicylic acid showed obvious subfamily preferences. Furthermore, three AhLEA genes, AhLEA1, AhLEA3-1, and AhLEA3-3, which were up-regulated by drought, low-temperature, or Al stresses was proved to enhance cold and Al tolerance in yeast, and AhLEA3-1 enhanced the drought tolerance in yeast.

CONCLUSIONS

AhLEAs are involved in abiotic stress response, and segmental duplication plays an important role in the evolution and amplification of AhLEAs. The genome-wide identification, classification, evolutionary and transcription analyses of the AhLEA gene family provide a foundation for further exploring the LEA genes' function in response to abiotic stress in peanuts.

LEA13 and LEA30 Are Involved in Tolerance to Water Stress and Stomata Density in Arabidopsis thaliana

Late embryogenesis abundant (LEA) proteins are a large protein family that mainly function in protecting cells from abiotic stress, but these proteins are also involved in regulating plant growth and development. In this study, we performed a functional analysis of LEA13 and LEA30 from Arabidopsis thaliana. The results showed that the expression of both genes increased when plants were subjected to drought-stressed conditions. The insertional lines lea13 and lea30 were identified for each gene, and both had a T-DNA element in the regulatory region, which caused the genes to be downregulated. Moreover, lea13 and lea30 were more sensitive to drought stress due to their higher transpiration and stomatal spacing. Microarray analysis of the lea13 background showed that genes involved in hormone signaling, stomatal development, and abiotic stress responses were misregulated. Our results showed that LEA proteins are involved in drought tolerance and participate in stomatal density.

TMEM106B in humans and Vac7 and Tag1 in yeast are predicted to be lipid transfer proteins

TMEM106B is an integral membrane protein of late endosomes and lysosomes involved in neuronal function, its overexpression being associated with familial frontotemporal lobar degeneration, and point mutation linked to hypomyelination. It has also been identified in multiple screens for host proteins required for productive SARS-CoV-2 infection. Because standard approaches to understand TMEM106B at the sequence level find no homology to other proteins, it has remained a protein of unknown function. Here, the standard tool PSI-BLAST was used in a nonstandard way to show that the lumenal portion of TMEM106B is a member of the late embryogenesis abundant-2 (LEA-2) domain superfamily. More sensitive tools (HMMER, HHpred, and trRosetta) extended this to predict LEA-2 domains in two yeast proteins. One is Vac7, a regulator of PI(3,5)P₂ production in the degradative vacuole, equivalent to the lysosome, which has a LEA-2 domain in its lumenal domain. The other is Tag1, another vacuolar protein, which signals to terminate autophagy and has three LEA-2 domains in its lumenal domain. Further analysis of LEA-2 structures indicated that LEA-2 domains have a long, conserved lipid-binding groove. This implies that TMEM106B, Vac7, and Tag1 may all be lipid transfer proteins in the lumen of late endocytic organelles.

Characterization of the Heat-Stable Proteome during Seed Germination in Arabidopsis with Special Focus on LEA Proteins

During seed germination, desiccation tolerance is lost in the radicle with progressing radicle protrusion and seedling establishment. This process is accompanied by comprehensive changes in the metabolome and proteome. Germination of Arabidopsis seeds was investigated over 72 h with special focus on the heat-stable proteome including late embryogenesis abundant (LEA) proteins together with changes in primary metabolites. Six metabolites in dry seeds known to be important for seed longevity decreased during germination and seedling establishment, while all other metabolites increased simultaneously with activation of growth and development. Thermo-stable proteins were associated with a multitude of biological processes. In the heat-stable proteome, a relatively similar proportion of fully ordered and fully intrinsically disordered proteins (IDP) was discovered. Highly disordered proteins were found to be associated with functional categories development, protein, RNA and stress. As expected, the majority of LEA proteins decreased during germination and seedling establishment. However, four germination-specific dehydrins were identified, not present in dry seeds. A network analysis of proteins, metabolites and amino acids generated during the course of germination revealed a highly connected LEA protein network.

Drought stress-induced physiological mechanisms, signaling pathways and molecular response of chloroplasts in common vegetable crops

Drought stress is one of the most adverse abiotic stresses that hinder plants' growth and productivity, threatening sustainable crop production. It impairs normal growth, disturbs water relations and reduces water-use efficiency in plants. However, plants have evolved many physiological and biochemical responses at the cellular and organism levels, in order to cope with drought stress. Photosynthesis, which is considered one of the most crucial biological processes for survival of plants, is greatly affected by drought stress. A gradual decrease in CO₂ assimilation rates, reduced leaf size, stem extension and root proliferation under drought stress, disturbs plant water relations, reducing water-use efficiency, disrupts photosynthetic pigments and reduces the gas exchange affecting the plants adversely. In such conditions, the chloroplast, organelle responsible for photosynthesis, is found to counteract the ill effects of drought stress by its critical involvement as a sensor of changes occurring in the environment, as the first process that drought stress affects is photosynthesis. Beside photosynthesis, chloroplasts carry out primary metabolic functions such as the biosynthesis of starch, amino acids, lipids, and tetrapyroles, and play a central role in the assimilation of nitrogen and sulfur. Because the chloroplasts are central organelles where the photosynthetic reactions take place, modifications in their physiology and protein pools are expected in response to the drought stress-induced variations in leaf gas exchanges and the accumulation of ROS. Higher expression levels of various transcription factors and other proteins including heat shock-related protein, LEA proteins seem to be regulating the heat tolerance mechanisms. However, several aspects of plastid alterations, following a water deficit environment are still poorly characterized. Since plants adapt to various stress tolerance mechanisms to respond to drought stress, understanding mechanisms of drought stress tolerance in plants will lead toward the development of drought tolerance in crop plants. This review throws light on major droughts stress-induced molecular/physiological mechanisms in response to severe and prolonged drought stress and addresses the molecular response of chloroplasts in common vegetable crops. It further highlights research gaps, identifying unexplored domains and suggesting recommendations for future investigations.

Interplay of Structural Disorder and Short Binding Elements in the Cellular Chaperone Function of Plant Dehydrin ERD14

Details of the functional mechanisms of intrinsically disordered proteins (IDPs) in living cells is an area not frequently investigated. Here, we dissect the molecular mechanism of action of an IDP in cells by detailed structural analyses based on an in-cell nuclear magnetic resonance experiment. We show that the ID stress protein (IDSP) A. thaliana Early Response to Dehydration (ERD14) is capable of protecting E. coli cells under heat stress. The overexpression of ERD14 increases the viability of E. coli cells from 38.9% to 73.9% following heat stress (50 °C × 15 min). We also provide evidence that the protection is mainly achieved by protecting the proteome of the cells. In-cell NMR experiments performed in E. coli cells show that the protective activity is associated with a largely disordered structural state with conserved, short sequence motifs (K- and H-segments), which transiently sample helical conformations in vitro and engage in partner binding in vivo. Other regions of the protein, such as its S segment and its regions linking and flanking the binding motifs, remain unbound and disordered in the cell. Our data suggest that the cellular function of ERD14 is compatible with its residual structural disorder in vivo.

The N-Terminal Region of Soybean PM1 Protein Protects Liposomes during Freeze-Thaw

Late embryogenesis abundant (LEA) group 1 (LEA_1) proteins are intrinsically disordered proteins (IDPs) that play important roles in protecting plants from abiotic stress. Their protective function, at a molecular level, has not yet been fully elucidated, but several studies suggest their involvement in membrane stabilization under stress conditions. In this paper, the soybean LEA_1 protein PM1 and its truncated forms (PM1-N: N-terminal half; PM1-C: C-terminal half) were tested for the ability to protect liposomes against damage induced by freeze-thaw stress. Turbidity measurement and light microscopy showed that full-length PM1 and PM1-N, but not PM1-C, can prevent freeze-thaw-induced aggregation of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) liposomes and native thylakoid membranes, isolated from spinach leaves (Spinacia oleracea). Particle size distribution analysis by dynamic light scattering (DLS) further confirmed that PM1 and PM1-N can prevent liposome aggregation during freeze-thaw. Furthermore, PM1 or PM1-N could significantly inhibit membrane fusion of liposomes, but not reduce the leakage of their contents following freezing stress. The results of proteolytic digestion and circular dichroism experiments suggest that PM1 and PM1-N proteins bind mainly on the surface of the POPC liposome. We propose that, through its N-terminal region, PM1 functions as a membrane-stabilizing protein during abiotic stress, and might inhibit membrane fusion and aggregation of vesicles or other endomembrane structures within the plant cell.

Similar Yet Different-Structural and Functional Diversity among Arabidopsis thaliana LEA_4 Proteins

The importance of intrinsically disordered late embryogenesis abundant (LEA) proteins in the tolerance to abiotic stresses involving cellular dehydration is undisputed. While structural transitions of LEA proteins in response to changes in water availability are commonly observed and several molecular functions have been suggested, a systematic, comprehensive and comparative study of possible underlying sequence-structure-function relationships is still lacking. We performed molecular dynamics (MD) simulations as well as spectroscopic and light scattering experiments to characterize six members of two distinct, lowly homologous clades of LEA_4 family proteins from Arabidopsis thaliana. We compared structural and functional characteristics to elucidate to what degree structure and function are encoded in LEA protein sequences and complemented these findings with physicochemical properties identified in a systematic bioinformatics study of the entire Arabidopsis thaliana LEA_4 family. Our results demonstrate that although the six experimentally characterized LEA_4 proteins have similar structural and functional characteristics, differences concerning their folding propensity and membrane stabilization capacity during a freeze/thaw cycle are obvious. These differences cannot be easily attributed to sequence conservation, simple physicochemical characteristics or the abundance of sequence motifs. Moreover, the folding propensity does not appear to be correlated with membrane stabilization capacity. Therefore, the refinement of LEA_4 structural and functional properties is likely encoded in specific patterns of their physicochemical characteristics.

Common Functions of Disordered Proteins across Evolutionary Distant Organisms

Intrinsically disordered proteins and regions typically lack a well-defined structure and thus fall outside the scope of the classic sequence–structure–function relationship. Hence, classic sequence- or structure-based bioinformatic approaches are often not well suited to identify homology or predict the function of unknown intrinsically disordered proteins. Here, we give selected examples of intrinsic disorder in plant proteins and present how protein function is shared, altered or distinct in evolutionary distant organisms. Furthermore, we explore how examining the specific role of disorder across different phyla can provide a better understanding of the common features that protein disorder contributes to the respective biological mechanism.

Isolation and characterization of an atypical LEA gene (IpLEA) from Ipomoea pes-caprae conferring salt/drought and oxidative stress tolerance

Late embryogenesis abundant (LEA) proteins belong to a large family that exists widely in plants and is mainly involved in desiccation processes during plant development or in the response to abiotic stresses. Here, we reported on an atypical LEA gene (IpLEA) related to salt tolerance from Ipomoea pes-caprae L. (Convolvulaceae). Sequence analysis revealed that IpLEA belongs to the LEA_2 (PF03168) group. IpLEA was shown to have a cytoplasmic localization pattern. Quantitative reverse transcription PCR analysis showed that IpLEA was widely expressed in different organs of the I. pes-caprae plants, and the expression levels increased following salt, osmotic, oxidative, freezing, and abscisic acid treatments. Analysis of the 1,495 bp promoter of IpLEA identified distinct cis-acting regulatory elements involved in abiotic stress. Induction of IpLEA improved Escherichia coli growth performance compared with the control under abiotic stresses. To further assess the function of IpLEA in plants, transgenic Arabidopsis plants overexpressing IpLEA were generated. The IpLEA-overexpressing Arabidopsis seedlings and adult plants showed higher tolerance to salt and drought stress than the wild-type. The transgenic plants also showed higher oxidative stress tolerance than the wild-type Arabidopsis. Furthermore, the expression patterns of a series of stress-responsive genes were affected. The results indicate that IpLEA is involved in the plant response to salt and drought, probably by mediating water homeostasis or by acting as a reactive oxygen species scavenger, thereby influencing physiological processes under various abiotic stresses in microorganisms and plants.

Protecting Enzymes from Stress-Induced Inactivation

The pharmaceutical and chemical industries depend on additives to protect enzymes and other proteins against stresses that accompany their manufacture, transport, and storage. Common stresses include vacuum-drying, freeze-thawing, and freeze-drying. The additives include sugars, compatible osmolytes, amino acids, synthetic polymers, and both globular and disordered proteins. Scores of studies have been published on protection, but the data have never been analyzed systematically. To spur efforts to understand the sources of protection and ultimately develop more effective formulations, we review ideas about the mechanisms of protection, survey the literature searching for patterns of protection, and then compare the ideas to the data.

Genome-wide identification of and functional insights into the late embryogenesis abundant (LEA) gene family in bread wheat (Triticum aestivum)

Late embryogenesis abundant (LEA) proteins are involved in the responses and adaptation of plants to various abiotic stresses, including dehydration, salinity, high temperature, and cold. Here, we report the first comprehensive survey of the LEA gene family in “Chinese Spring” wheat (Triticum aestivum). A total of 179 TaLEA genes were identified in T. aestivum and classified into eight groups. All TaLEA genes harbored the LEA conserved motif and had few introns. TaLEA genes belonging to the same group exhibited similar gene structures and chromosomal locations. Our results revealed that most TaLEA genes contained abscisic acid (ABA)-responsive elements (ABREs) and various cis-acting elements associated with the stress response in the promoter region and were induced under ABA and abiotic stress treatments. In addition, 8 genes representing each group were introduced into E. coli and yeast to investigate the protective function of TaLEAs under heat and salt stress. TaLEAs enhanced the tolerance of E. coli and yeast to salt and heat, indicating that these proteins have protective functions in host cells under stress conditions. These results increase our understanding of LEA genes and provide robust candidate genes for future functional investigations aimed at improving the stress tolerance of wheat.

A late embryogenesis abundant protein GsPM30 interacts with a receptor like cytoplasmic kinase GsCBRLK and regulates environmental stress responses

A Glycine soja receptor like cytoplasmic kinase GsCBRLK was previously characterized as a positive regulator of salt tolerance. However, how GsCBRLK regulates stress responses remains obscure. Here, we report the interaction between GsCBRLK and a group 3 late embryogenesis abundant protein GsPM30, and suggest its role in stress responses. GsPM30 was found to physically associate with GsCBRLK through yeast two hybrid assays, which was verified by bimolecular fluorescence complementation analysis. Deletion analyses showed that the N-terminal variable domain of GsCBRLK was sufficient for GsPM30 interaction. Besides GsPM30, GsCBRLK could associate with several group 3 LEAs, of which the N-terminus sequences show high identity with GsPM30. Lower binding affinity or even no interaction was observed between GsCBRLK and other group 3 LEAs, which are less closely related to GsPM30. Furthermore, we observed that GsPM30 could localize surrounding the internal circumference of plant cells, as well as in cytoplasm and nucleus. In addition, GUS staining and quantitative real-time PCR results suggested the ubiquitous expression in different tissues and induced expression by NaCl and mannitol treatments for GsPM30. Consistently, GsPM30 overexpression in Arabidopsis caused increased tolerance to high salinity and dehydration/water deficit at both the young and adult seedling stages. Our results demonstrated the interaction between GsCBRLK and LEAs, and revealed the positive role of GsPM30 in stress responses.

Sequence composition versus sequence order in the cryoprotective function of an intrinsically disordered stress-response protein

Intrinsically disordered stress proteins have been shown to act as chaperones, protecting proteins from damage caused by stresses such as freezing and thawing. Dehydration proteins (dehydrins) are intrinsically disordered stress proteins that are found in almost all land plants. They consist of a variable number of the short, semi-conserved, Y-, S-, and K-segments, with longer stretches of poorly conserved sequences in between. Previous studies have provided conflicting views on the details of the dehydrin cryoprotective mechanism of enzymes. Experiments with polyethylene glycol (PEG) have shown that PEG cryoprotective efficiency is the same as dehydrins of the same hydrodynamic radius, suggesting that the protein's disordered and polar nature is important, rather than the specific order of the residues. To further elucidate the mechanism, we created scrambled variants of the wild grape dehydrins K₂ and YSK₂ and tested their ability to protect lactate dehydrogenase and yeast frataxin homolog-1 from freeze/thaw damage. The results show that for preventing aggregation, it is the sequence composition and the size of the dehydrin that is the most important factor in protection, while for freeze/thaw damage causing loss of secondary structure, it is the sequence composition that is most significant.

Selection of reference genes for quantitative real-time PCR analysis in cucumber (Cucumis sativus L.), pumpkin (Cucurbita moschata Duch.) and cucumber-pumpkin grafted plants

Background

Quantitative real-time PCR (qRT-PCR) is a commonly used high-throughput technique to measure mRNA transcript levels. The accuracy of this evaluation of gene expression depends on the use of optimal reference genes. Cucumber-pumpkin grafted plants, made by grafting a cucumber scion onto pumpkin rootstock, are superior to either parent plant, as grafting conveys many advantages. However, although many reliable reference genes have been identified in both cucumber and pumpkin, none have been obtained for cucumber-pumpkin grafted plants.

Methods

In this work, 12 candidate reference genes, including eight traditional genes and four novel genes identified from our transcriptome data, were selected to assess their expression stability. Their expression levels in 25 samples, including three cucumber and three pumpkin samples from different organs, and 19 cucumber-pumpkin grafted samples from different organs, conditions, and varieties, were analyzed by qRT-PCR, and the stability of their expression was assessed by the comparative ΔCt method, geNorm, NormFinder, BestKeeper, and RefFinder.

Results

The results showed that the most suitable reference gene varied dependent on the organs, conditions, and varieties. CACS and 40SRPS8 were the most stable reference genes for all samples in our research. TIP41 and CACS showed the most stable expression in different cucumber organs, TIP41 and PP2A were the optimal reference genes in pumpkin organs, and CACS and 40SRPS8 were the most stable genes in all grafted cucumber samples. However, the optimal reference gene varied under different conditions. CACS and 40SRPS8 were the best combination of genes in different organs of cucumber-pumpkin grafted plants, TUA and RPL36Aa were the most stable in the graft union under cold stress, LEA26 and ARF showed the most stable expression in the graft union during the healing process, and TIP41 and PP2A were the most stable across different varieties of cucumber-pumpkin grafted plants. The use of LEA26, ARF and LEA26+ARF as reference genes were further verified by analyzing the expression levels of csaCYCD3;1, csaRUL, cmoRUL, and cmoPIN in the graft union at different time points after grafting.

Discussion

This work is the first report of appropriate reference genes in grafted cucumber plants and provides useful information for the study of gene expression and molecular mechanisms in cucumber-pumpkin grafted plants.

GmSYP24, a putative syntaxin gene, confers osmotic/drought, salt stress tolerances and ABA signal pathway

As major environment factors, drought or high salinity affect crop growth, development and yield. Transgenic approach is an effective way to improve abiotic stress tolerance of crops. In this study, we comparatively analyzed gene structures, genome location, and the evolution of syntaxin proteins containing late embryogenesis abundant (LEA2) domain. GmSYP24 was identified as a dehydration-responsive gene. Our study showed that the GmSYP24 protein was located on the cell membrane. The overexpression of GmSYP24 (GmSYP24ox) in soybean and heteroexpression of GmSYP24 (GmSYP24hx) in Arabidopsis exhibited insensitivity to osmotic/drought and high salinity. However, wild type soybean, Arabidopsis, and the mutant of GmSYP24 homologous gene of Arabidopsis were sensitive to the stresses. Under the abiotic stresses, transgenic soybean plants had greater water content and higher activities of POD, SOD compared with non-transgenic controls. And the leaf stomatal density and opening were reduced in transgenic Arabidopsis. The sensitivity to ABA was decreased during seed germination of GmSYP24ox and GmSYP24hx. GmSYP24hx induced up-regulation of ABA-responsive genes. GmSYP24ox alters the expression of some aquaporins under osmotic/drought, salt, or ABA treatment. These results demonstrated that GmSYP24 played an important role in osmotic/drought or salt tolerance in ABA signal pathway.

Protecting activity of desiccated enzymes

Protein-based biological drugs and many industrial enzymes are unstable, making them prohibitively expensive. Some can be stabilized by formulation with excipients, but most still require low temperature storage. In search of new, more robust excipients, we turned to the tardigrade, a microscopic animal that synthesizes cytosolic abundant heat soluble (CAHS) proteins to protect its cellular components during desiccation. We find that CAHS proteins protect the test enzymes lactate dehydrogenase and lipoprotein lipase against desiccation-, freezing-, and lyophilization-induced deactivation. Our data also show that a variety of globular and disordered protein controls, with no known link to desiccation tolerance, protect our test enzymes. Protection of lactate dehydrogenase correlates, albeit imperfectly, with the charge density of the protein additive, suggesting an approach to tune protection by modifying charge. Our results support the potential use of CAHS proteins as stabilizing excipients in formulations and suggest that other proteins may have similar potential.

Involvement of HbMC1-mediated cell death in tapping panel dryness of rubber tree (Hevea brasiliensis)

Tapping panel dryness (TPD) causes a significant reduction in the latex yield of rubber tree (Hevea brasiliensis Muell. Arg.). It is reported that TPD is a typical programmed cell death (PCD) process. Although PCD plays a vital role in TPD occurrence, there is a lack of detailed and systematic study. Metacaspases are key regulators of diverse PCD in plants. Based on our previous result that HbMC1 was associated with TPD, we further elucidate the roles of HbMC1 on rubber tree TPD in this study. HbMC1 was up-regulated by TPD-inducing factors including wounding, ethephon and H2O2. Moreover, the expression level of HbMC1 was increased along with TPD severity in rubber tree, suggesting a positive correlation between HbMC1 expression and TPD severity. To investigate its biological function, HbMC1 was overexpressed in yeast (Saccharomyces cerevisiae) and tobacco (Nicotiana benthamiana). Transgenic yeast and tobacco overexpressing HbMC1 showed growth retardation compared with controls under H2O2-induced oxidative stress. In addition, overexpression of HbMC1 in yeast and tobacco reduced cell survival after high-concentration H2O2 treatment and resulted in enhanced H2O2-induced leaf cell death, respectively. A total of 11 proteins, rbcL, TM9SF2-like, COX3, ATP9, DRP, HbREF/Hevb1, MSSP2-like, SRC2, GATL8, CIPK14-like and STK, were identified and confirmed to interact with HbMC1 by yeast two-hybrid screening and co-transformation in yeast. The 11 proteins mentioned above are associated with many biological processes, including rubber biosynthesis, stress response, autophagy, carbohydrate metabolism, signal transduction, etc. Taken together, our results suggest that HbMC1-mediated PCD plays an important role in rubber tree TPD, and the identified HbMC1-interacting proteins provide valuable information for further understanding the molecular mechanism of HbMC1-mediated TPD in rubber tree.

Associating transcriptional regulation for rapid germination of rapeseed (Brassica napus L.) under low temperature stress through weighted gene co-expression network analysis

Slow germination speed caused by low temperature stress intensifies the risk posed by adverse environmental factors, contributing to low germination rate and reduced production of rapeseed. The purpose of this study was to understand the transcriptional regulation mechanism for rapid germination of rapeseed. The results showed that seed components and size do not determine the seed germination speed. Different temporal transcriptomic profiles were generated under normal and low temperature conditions in genotypes with fast and slow germination speeds. Using weight gene co-expression network analysis, 37 823 genes were clustered into 15 modules with different expression patterns. There were 10 233 and 9111 differentially expressed genes found to follow persistent tendency of up- and down-regulation, respectively, which provided the conditions necessary for germination. Hub genes in the continuous up-regulation module were associated with phytohormone regulation, signal transduction, the pentose phosphate pathway, and lipolytic metabolism. Hub genes in the continuous down-regulation module were involved in ubiquitin-mediated proteolysis. Through pairwise comparisons, 1551 specific upregulated DEGs were identified for the fast germination speed genotype under low temperature stress. These DEGs were mainly enriched in RNA synthesis and degradation metabolisms, signal transduction, and defense systems. Transcription factors, including WRKY, bZIP, EFR, MYB, B3, DREB, NAC, and ERF, are associated with low temperature stress in the fast germination genotype. The aquaporin NIP5 and late embryogenesis abundant (LEA) protein genes contributed to the water uptake and transport under low temperature stress during seed germination. The ethylene/H₂O₂-mediated signal pathway plays an important role in cell wall loosening and embryo extension during germination. The ROS-scavenging system, including catalase, aldehyde dehydrogenase, and glutathione S-transferase, was also upregulated to alleviate ROS toxicity in the fast germinating genotype under low temperature stress. These findings should be useful for molecular assisted screening and breeding of fast germination speed genotypes for rapeseed.

Integrative analysis of the late maturation programme and desiccation tolerance mechanisms in intermediate coffee seeds

The 'intermediate seed' category was defined in the early 1990s using coffee (Coffea arabica) as a model. In contrast to orthodox seeds, intermediate seeds cannot survive complete drying, which is a major constraint for seed storage and has implications for both biodiversity conservation and agricultural purposes. However, intermediate seeds are considerably more tolerant to drying than recalcitrant seeds, which are highly sensitive to desiccation. To gain insight into the mechanisms governing such differences, changes in desiccation tolerance (DT), hormone contents, and the transcriptome were analysed in developing coffee seeds. Acquisition of DT coincided with a dramatic transcriptional switch characterised by the repression of primary metabolism, photosynthesis, and respiration, and the up-regulation of genes coding for late-embryogenesis abundant (LEA) proteins, heat-shock proteins (HSPs), and antioxidant enzymes. Analysis of the heat-stable proteome in mature coffee seeds confirmed the accumulation of LEA proteins identified at the transcript level. Transcriptome analysis also suggested a major role for ABA and for the transcription factors CaHSFA9, CaDREB2G, CaANAC029, CaPLATZ, and CaDOG-like in DT acquisition. The ability of CaHSFA9 and CaDREB2G to trigger HSP gene transcription was validated by Agrobacterium-mediated transformation of coffee somatic embryos.

Molecular Cloning and Functional Characterization of the Dehydrin (IpDHN) Gene From Ipomoea pes-caprae

Dehydrin (DHN) genes can be rapidly induced to offset water deficit stresses in plants. Here, we reported on a dehydrin gene (IpDHN) related to salt tolerance isolated from Ipomoea pes-caprae L. (Convolvulaceae). The IpDHN protein shares a relatively high homology with Arabidopsis dehydrin ERD14 (At1g76180). IpDHN was shown to have a cytoplasmic localization pattern. Quantitative RT-PCR analyses indicated that IpDHN was differentially expressed in most organs of I. pes-caprae plants, and its expression level increased after salt, osmotic stress, oxidative stress, cold stress and ABA treatments. Analysis of the 974-bp promoter of IpDHN identified distinct cis-acting regulatory elements, including an MYB binding site (MBS), ABRE (ABA responding)-elements, Skn-1 motif, and TC-rich repeats. The induced expression of IpDHN in Escherichia coli indicated that IpDHN might be involved in salt, drought, osmotic, and oxidative stresses. We also generated transgenic Arabidopsis lines that over-expressed IpDHN. The transgenic Arabidopsis plants showed a significant enhancement in tolerance to salt/drought stresses, as well as less accumulation of hydrogen peroxide (H₂O₂) and the superoxide radical (O₂ ^-), accompanied by increasing activity of the antioxidant enzyme system in vivo. Under osmotic stresses, the overexpression of IpDHN in Arabidopsis can elevate the expression of ROS-related and stress-responsive genes and can improve the ROS-scavenging ability. Our results indicated that IpDHN is involved in cellular responses to salt and drought through a series of pleiotropic effects that are likely involved in ROS scavenging and therefore influence the physiological processes of microorganisms and plants exposed to many abiotic stresses.

Tardigrades Use Intrinsically Disordered Proteins to Survive Desiccation

Tardigrades are microscopic animals that survive a remarkable array of stresses, including desiccation. How tardigrades survive desiccation has remained a mystery for more than 250 years. Trehalose, a disaccharide essential for several organisms to survive drying, is detected at low levels or not at all in some tardigrade species, indicating that tardigrades possess potentially novel mechanisms for surviving desiccation. Here we show that tardigrade-specific intrinsically disordered proteins (TDPs) are essential for desiccation tolerance. TDP genes are constitutively expressed at high levels or induced during desiccation in multiple tardigrade species. TDPs are required for tardigrade desiccation tolerance, and these genes are sufficient to increase desiccation tolerance when expressed in heterologous systems. TDPs form non-crystalline amorphous solids (vitrify) upon desiccation, and this vitrified state mirrors their protective capabilities. Our study identifies TDPs as functional mediators of tardigrade desiccation tolerance, expanding our knowledge of the roles and diversity of disordered proteins involved in stress tolerance.

Involvement of C-Terminal Histidines in Soybean PM1 Protein Oligomerization and Cu2+ Binding

Late embryogenesis abundant (LEA) proteins are widely distributed among plant species, where they contribute to abiotic stress tolerance. LEA proteins can be classified into seven groups according to conserved sequence motifs. The PM1 protein from soybean, which belongs to the Pfam LEA_1 group, has been shown previously to be at least partially natively unfolded, to bind metal ions and potentially to stabilize proteins and membranes. Here, we investigated the role of the PM1 C-terminal domain and in particular the multiple histidine residues in this half of the protein. We constructed recombinant plasmids expressing full-length PM1 and two truncated forms, PM1-N and PM1-C, which represent the N- and C-terminal halves of the protein, respectively. Immunoblotting and cross-linking experiments showed that full-length PM1 forms oligomers and high molecular weight (HMW) complexes in vitro and in vivo, while PM1-C, but not PM1-N, also formed oligomers and HMW complexes in vitro. When the histidine residues in PM1 and PM1-C were chemically modified, oligomerization was abolished, suggesting that histidines play a key role in this process. Furthermore, we demonstrated that high Cu2+ concentrations promote oligomerization and induce PM1 and PM1-C to form HMW complexes. Therefore, we speculate that PM1 proteins not only maintain ion homeostasis in the cytoplasm, but also potentially stabilize and protect other proteins during abiotic stress by forming a large, oligomeric molecular shield around biological targets.

Insights on Structure and Function of a Late Embryogenesis Abundant Protein from Amaranthus cruentus: An Intrinsically Disordered Protein Involved in Protection against Desiccation, Oxidant Conditions, and Osmotic Stress

Late embryogenesis abundant (LEA) proteins are part of a large protein family that protect other proteins from aggregation due to desiccation or osmotic stresses. Recently, the Amaranthus cruentus seed proteome was characterized by 2D-PAGE and one highly accumulated protein spot was identified as a LEA protein and was named AcLEA. In this work, AcLEA cDNA was cloned into an expression vector and the recombinant protein was purified and characterized. AcLEA encodes a 172 amino acid polypeptide with a predicted molecular mass of 18.34 kDa and estimated pI of 8.58. Phylogenetic analysis revealed that AcLEA is evolutionarily close to the LEA3 group. Structural characteristics were revealed by nuclear magnetic resonance and circular dichroism methods. We have shown that recombinant AcLEA is an intrinsically disordered protein in solution even at high salinity and osmotic pressures, but it has a strong tendency to take a secondary structure, mainly folded as α-helix, when an inductive additive is present. Recombinant AcLEA function was evaluated using Escherichia coli as in vivo model showing the important protection role against desiccation, oxidant conditions, and osmotic stress. AcLEA recombinant protein was localized in cytoplasm of Nicotiana benthamiana protoplasts and orthologs were detected in seeds of wild and domesticated amaranth species. Interestingly AcLEA was detected in leaves, stems, and roots but only in plants subjected to salt stress. This fact could indicate the important role of AcLEA protection during plant stress in all amaranth species studied.

Functional insights into the late embryogenesis abundant (LEA) protein family from Dendrobium officinale (Orchidaceae) using an Escherichia coli system

Late embryogenesis abundant (LEA) proteins, a diverse family, accumulate during seed desiccation in the later stages of embryogenesis. LEA proteins are associated with tolerance to abiotic stresses, such as drought, salinity and high or cold temperature. Here, we report the first comprehensive survey of the LEA gene family in Dendrobium officinale, an important and widely grown medicinal orchid in China. Based on phylogenetic relationships with the complete set of Arabidopsis and Oryza LEA proteins, 17 genes encoding D. officinale LEAs (DofLEAs) were identified and their deduced proteins were classified into seven groups. The motif composition of these deduced proteins was correlated with the gene structure found in each LEA group. Our results reveal the DofLEA genes are widely distributed and expressed in tissues. Additionally, 11 genes from different groups were introduced into Escherichia coli to assess the functions of DofLEAs. Expression of 6 and 7 DofLEAs in E. coli improved growth performance compared with the control under salt and heat stress, respectively. Based on qPCR data, all of these genes were up-regulated in various tissues following exposure to salt and heat stresses. Our results suggest that DofLEAs play an important role in responses to abiotic stress.

Characterization of OsLEA1a and its inhibitory effect on the resistance of E. coli to diverse abiotic stresses

OsLEA1a is a late embryogenesis abundant (LEA) protein gene from Oryza sativa L, which contains an open reading frame of 282-bp that encodes a putative polypeptide of 93 amino acids. OsLEA1a protein contains abundant of Lys, Ala, Glu, Asp, Gly, Arg and Leu, but depleted in Cys, His, Phe, Trp and Tyr residues; and is strongly hydrophilic. OsLEA1a includes six helical domains and a β-sheet domain. Real-time PCR analysis showed that OsLEA1a was expressed in roots, leaves and panicles of rice, with no or only a few transcripts in stem tissues, and remained at a relatively higher level in leaves during the tillering period, the heading period, the filling period and the full ripe period. To make sense of OsLEA1a functions, TrxA-OsLEA1a fusion protein expression vector and OsLEA1a protein expression vector were transformed into Escherichia coli DL21 (DE3), respectively. The accumulation of the TrxA-OsLEA1a fusion protein or OsLEA1a protein interfered with the resistance of E. coli to high salinity, metal ions, hyperosmotic, oxidation, heat and freeze-thaw stresses. The purified TrxA-OsLEA1a fusion protein reduced stabilization of LDH and increased damage of diverse abiotic stresses to LDH. The findings suggested that the OsLEA1a may confor antibacterial activity under abiotic stresses.

The Unstructured N-terminal Region of Arabidopsis Group 4 Late Embryogenesis Abundant (LEA) Proteins Is Required for Folding and for Chaperone-like Activity under Water Deficit

Late embryogenesis abundant (LEA) proteins are a conserved group of proteins widely distributed in the plant kingdom that participate in the tolerance to water deficit of different plant species. In silico analyses indicate that most LEA proteins are structurally disordered. The structural plasticity of these proteins opens the question of whether water deficit modulates their conformation and whether these possible changes are related to their function. In this work, we characterized the secondary structure of Arabidopsis group 4 LEA proteins. We found that they are disordered in aqueous solution, with high intrinsic potential to fold into α-helix. We demonstrate that complete dehydration is not required for these proteins to sample ordered structures because milder water deficit and macromolecular crowding induce high α-helix levels in vitro, suggesting that prevalent conditions under water deficit modulate their conformation. We also show that the N-terminal region, conserved across all group 4 LEA proteins, is necessary and sufficient for conformational transitions and that their protective function is confined to this region, suggesting that folding into α-helix is required for chaperone-like activity under water limitation. We propose that these proteins can exist as different conformers, favoring functional diversity, a moonlighting property arising from their structural dynamics.

Functional characterization of the late embryogenesis abundant (LEA) protein gene family from Pinus tabuliformis (Pinaceae) in Escherichia coli

Late embryogenesis abundant (LEA) proteins are a large and highly diverse gene family present in a wide range of plant species. LEAs are proposed to play a role in various stress tolerance responses. Our study represents the first-ever survey of LEA proteins and their encoding genes in a widely distributed pine (Pinus tabuliformis) in China. Twenty-three LEA genes were identified from the P. tabuliformis belonging to seven groups. Proteins with repeated motifs are an important feature specific to LEA groups. Ten of 23 pine LEA genes were selectively expressed in specific tissues, and showed expression divergence within each group. In addition, we selected 13 genes representing each group and introduced theses genes into Escherichia coli to assess the protective function of PtaLEA under heat and salt stresses. Compared with control cells, the E. coli cells expressing PtaLEA fusion protein exhibited enhanced salt and heat resistance and viability, indicating the protein may play a protective role in cells under stress conditions. Furthermore, among these enhanced tolerance genes, a certain extent of function divergence appeared within a gene group as well as between gene groups, suggesting potential functional diversity of this gene family in conifers.

Study of model systems to test the potential function of Artemia group 1 late embryogenesis abundant (LEA) proteins

Embryos of the brine shrimp, Artemia franciscana, are genetically programmed to develop either ovoviparously or oviparously depending on environmental conditions. Shortly upon their release from the female, oviparous embryos enter diapause during which time they undergo major metabolic rate depression while simultaneously synthesize proteins that permit them to tolerate a wide range of stressful environmental events including prolonged periods of desiccation, freezing, and anoxia. Among the known stress-related proteins that accumulate in embryos entering diapause are the late embryogenesis abundant (LEA) proteins. This large group of intrinsically disordered proteins has been proposed to act as molecular shields or chaperones of macromolecules which are otherwise intolerant to harsh conditions associated with diapause. In this research, we used two model systems to study the potential function of the group 1 LEA proteins from Artemia. Expression of the Artemia group 1 gene (AfrLEA-1) in Escherichia coli inhibited growth in proportion to the number of 20-mer amino acid motifs expressed. As well, clones of E. coli, transformed with the AfrLEA-1 gene, expressed multiple bands of LEA proteins, either intrinsically or upon induction with isopropyl-β-thiogalactoside (IPTG), in a vector-specific manner. Expression of AfrLEA-1 in E. coli did not overcome the inhibitory effects of high concentrations of NaCl and KCl but modulated growth inhibition resulting from high concentrations of sorbitol in the growth medium. In contrast, expression of the AfrLEA-1 gene in Saccharomyces cerevisiae did not alter the growth kinetics or permit yeast to tolerate high concentrations of NaCl, KCl, or sorbitol. However, expression of AfrLEA-1 in yeast improved its tolerance to drying (desiccation) and freezing. Under our experimental conditions, both E. coli and S. cerevisiae appear to be potentially suitable hosts to study the function of Artemia group 1 LEA proteins under environmentally stressful conditions.

A plant cell model of polyglutamine aggregation: Identification and characterisation of macromolecular and small-molecule anti-protein aggregation activity in vivo

In vitro studies have shown that LEA proteins from plants and invertebrates protect and stabilise other proteins under conditions of water stress, suggesting a role in stress tolerance. However, there is little information on LEA protein function in whole plants or plant cells, particularly with respect to their anti-aggregation activity. To address this, we expressed in tobacco BY-2 suspension cells an aggregation-prone protein based on that responsible for Huntington's disease (HD). In HD, abnormally long stretches of polyglutamine (polyQ) in huntingtin (Htt) protein cause aggregation of Htt fragments within cells. We constructed stably transformed BY-2 cell lines expressing enhanced green fluorescent protein (EGFP)-HttQ23 or EGFP-HttQ52 fusion proteins (encoding 23 or 52 glutamine residues, pertaining to the normal and disease states, respectively), as well as an EGFP control. EGFP-HttQ52 protein aggregated in the cytoplasm of transformed tobacco cells, which showed slow growth kinetics; in contrast, EGFP-HttQ23 or EGFP did not form aggregates and cells expressing these constructs grew normally. To test the effect of LEA proteins on protein aggregation in plant cells, we constructed cell lines expressing both EGFP-HttQ52 and LEA proteins (PM1, PM18, ZLDE-2 or AavLEA1) or a sHSP (PM31). Of these, AavLEA1 and PM31 reduced intracellular EGFP-HttQ52 aggregation and alleviated the associated growth inhibition, while PM18 and ZLDE-2 partially restored growth rates. Treatment of EGFP-HttQ52-expressing BY2 cells with the polyphenol epigallocatechin-3-gallate (EGCG) also reduced EGFP-HttQ52 aggregation and improved cell growth rate. The EGFP-HttQ52 cell line therefore has potential for characterising both macromolecular and small molecule inhibitors of protein aggregation in plant cells.

Characterization of Arabidopsis Transcriptional Responses to Different Aphid Species Reveals Genes that Contribute to Host Susceptibility and Non-host Resistance

Aphids are economically important pests that display exceptional variation in host range. The determinants of diverse aphid host ranges are not well understood, but it is likely that molecular interactions are involved. With significant progress being made towards understanding host responses upon aphid attack, the mechanisms underlying non-host resistance remain to be elucidated. Here, we investigated and compared Arabidopsis thaliana host and non-host responses to aphids at the transcriptional level using three different aphid species, Myzus persicae, Myzus cerasi and Rhopalosiphum pisum. Gene expression analyses revealed a high level of overlap in the overall gene expression changes during the host and non-host interactions with regards to the sets of genes differentially expressed and the direction of expression changes. Despite this overlap in transcriptional responses across interactions, there was a stronger repression of genes involved in metabolism and oxidative responses specifically during the host interaction with M. persicae. In addition, we identified a set of genes with opposite gene expression patterns during the host versus non-host interactions. Aphid performance assays on Arabidopsis mutants that were selected based on our transcriptome analyses identified novel genes contributing to host susceptibility, host defences during interactions with M. persicae as well to non-host resistance against R. padi. Understanding how plants respond to aphid species that differ in their ability to infest plant species, and identifying the genes and signaling pathways involved, is essential for the development of novel and durable aphid control in crop plants.

Aphids are phloem-feeding insects that cause feeding damage and transmit plant viruses to many crops. While most aphid species are restricted to one or few host plants, some aphids can infest a wide range of plant species. These insects spend a considerable time on non-hosts, where they probe the leaf tissue and secrete saliva, but for unknown reasons are unable to ingest phloem sap. This suggests that aphids interact with non-host plants at the molecular level, but potentially do not suppress plant defences and/or promote the release of nutrients. We compared gene expression of plants during host and non-host interactions with aphids to identify genes involved in immunity. We found significant overlap in the plant responses to aphids regardless of the type of interaction. Despite this, we identified a set of genes specifically affected during host or non-host interactions with specific aphid species. In addition, we showed that several of these genes contribute to host and/or non-host immunity. These findings are important, as they advance our understanding of the plant cellular processes involved in host and non-host responses against insect pests. Understanding mechanisms of host and non-host resistance to plant parasites is essential for development of novel control strategies.

The intrinsically disordered protein LEA7 from Arabidopsis thaliana protects the isolated enzyme lactate dehydrogenase and enzymes in a soluble leaf proteome during freezing and drying

The accumulation of Late Embryogenesis Abundant (LEA) proteins in plants is associated with tolerance against stresses such as freezing and desiccation. Two main functions have been attributed to LEA proteins: membrane stabilization and enzyme protection. We have hypothesized previously that LEA7 from Arabidopsis thaliana may stabilize membranes because it interacts with liposomes in the dry state. Here we show that LEA7, contrary to this expectation, did not stabilize liposomes during drying and rehydration. Instead, it partially preserved the activity of the enzyme lactate dehydrogenase (LDH) during drying and freezing. Fourier-transform infrared (FTIR) spectroscopy showed no evidence of aggregation of LDH in the dry or rehydrated state under conditions that lead to complete loss of activity. To approximate the complex influence of intracellular conditions on the protective effects of a LEA protein in a convenient in-vitro assay, we measured the activity of two Arabidopsis enzymes (glucose-6-P dehydrogenase and ADP-glucose pyrophosphorylase) in total soluble leaf protein extract (Arabidopsis soluble proteome, ASP) after drying and rehydration or freezing and thawing. LEA7 partially preserved the activity of both enzymes under these conditions, suggesting its role as an enzyme protectant in vivo. Further FTIR analyses indicated the partial reversibility of protein aggregation in the dry ASP during rehydration. Similarly, aggregation in the dry ASP was strongly reduced by LEA7. In addition, mixtures of LEA7 with sucrose or verbascose reduced aggregation more than the single additives, presumably through the effects of the protein on the H-bonding network of the sugar glasses.

Systematic mining of salt-tolerant genes in halophyte-Zoysia matrella through cDNA expression library screening

Though a large number of salt-tolerant genes were identified from Glycophyte in previous study, genes involved in salt-tolerance of halophyte were scarcely studied. In this report, an important halophyte turfgrass, Zoysia matrella, was used for systematic excavation of salt-tolerant genes using full-length cDNA expression library in yeast. Adopting the Gateway-compatible vector system, a high quality entry library was constructed, containing 3 × 10(6) clones with an average inserted fragments length of 1.64 kb representing a 100% full-length rate. The yeast expression library was screened in a salt-sensitive yeast mutant. The screening yielded dozens of salt-tolerant clones harboring 16 candidate salt-tolerant genes. Under salt-stress condition, these 16 genes exhibited different transcription levels. According to the results, we concluded that the salt-tolerance of Z. matrella might result from known genes involved in ion regulation, osmotic adjustment, as well as unknown pathway associated with protein folding and modification, RNA metabolism, and mitochondrial membrane translocase, etc. In addition, these results shall provide new insight for the future researches with respect to salt-tolerance.

Expression of the moss PpLEA4-20 gene in rice enhances membrane protection and client proteins stability

Green vegetative tissues of the moss Physcomitrella patens possess a powerful ability to tolerate severe drought stress. Proteomics analysis have revealed that a large number of late embryogenesis abundant (LEA) proteins were key players in the drought tolerance of the photosynthetic tissues. PpLEA4-20, a member of the moss LEA protein family, was selected for further function study using an ectopic expression method in rice. Through molecular identification via PCR, southern blotting and TAIL-PCR, we demonstrated that the PpLEA4-20 gene was transformed and inserted into a non-encoded region in chromosome 4 of rice and expressed stably in transgenic rice. Unexpectedly, PpLEA4-20 protein emerged as two high-expressed spots on 2-D gels generated from transgenic rice, suggesting that PpLEA4-20 proteins are complete compatible and might be modified in rice. Both growth and physiological analysis showed that seedlings of transgenic PpLEA4-20 rice displayed altered phenotypes and tolerance to salt. In addition, electrolyte leakage was reduced in transgenic PpLEA4-20 compared to wild type under stress conditions. Anti-aggregation analysis found that the PpLEA4-20 protein expressed in rice remained soluble at high temperature and in addition to some native proteins from transgenic PpLEA4-20 rice. Based on Nano LC MS/MS analysis, we identified several proteins from transgenic PpLEA4-20 rice of increased heat-stability. Our results provide evidence for a role of PpLEA4-20 in salt tolerance and stabilization of client proteins.

Overexpression of ShDHN, a dehydrin gene from Solanum habrochaites enhances tolerance to multiple abiotic stresses in tomato

Dehydrins (DHNs) play important roles in plant adaptation to abiotic stress. In this study, a cold-induced SK3-type DHN gene (ShDHN) isolated from wild tomato species Solanum habrochaites was characterized for its function in abiotic stress tolerance. ShDHN was constitutively expressed in root, leaf, stem, flower and fruit. ShDHN was continuously up-regulated during cold stress and showed higher expression level in the cold-tolerant S. habrochaites than in the susceptible S. lycopersicum. Moreover, ShDHN expression was also regulated by drought, salt, osmotic stress, and exogenous signaling molecules. Overexpression of ShDHN in cultivated tomato increased tolerance to cold and drought stresses and improved seedling growth under salt and osmotic stresses. Compared with the wild-type, the transgenic plants accumulated more proline, maintained higher enzymatic activities of superoxide dismutase and catalase, and suffered less membrane damage under cold and drought stresses. Moreover, the transgenic plants accumulated lower levels of H2O2 and O2(-) under cold stress, and had higher relative water contents and lower water loss rates under dehydration conditions. Furthermore, overexpression of ShDHN in tomato led to the up- or down-regulated expression of several genes involved in ROS scavenging and JA signaling pathway, including SOD1, GST, POD, LOX, PR1 and PR2. Taken together, these results indicate that ShDHN has pleiotropic effects on improving plant adaptation to abiotic stresses and that it possesses potential usefulness in genetic improvement of stress tolerance in tomato.

Comparison of amino acids physico-chemical properties and usage of late embryogenesis abundant proteins, hydrophilins and WHy domain

Late Embryogenesis Abundant proteins (LEAPs) comprise several diverse protein families and are mostly involved in stress tolerance. Most of LEAPs are intrinsically disordered and thus poorly functionally characterized. LEAPs have been classified and a large number of their physico-chemical properties have been statistically analyzed. LEAPs were previously proposed to be a subset of a very wide family of proteins called hydrophilins, while a domain called WHy (Water stress and Hypersensitive response) was found in LEAP class 8 (according to our previous classification). Since little is known about hydrophilins and WHy domain, the cross-analysis of their amino acids physico-chemical properties and amino acids usage together with those of LEAPs helps to describe some of their structural features and to make hypothesis about their function. Physico-chemical properties of hydrophilins and WHy domain strongly suggest their role in dehydration tolerance, probably by interacting with water and small polar molecules. The computational analysis reveals that LEAP class 8 and hydrophilins are distinct protein families and that not all LEAPs are a protein subset of hydrophilins family as proposed earlier. Hydrophilins seem related to LEAP class 2 (also called dehydrins) and to Heat Shock Proteins 12 (HSP12). Hydrophilins are likely unstructured proteins while WHy domain is structured. LEAP class 2, hydrophilins and WHy domain are thus proposed to share a common physiological role by interacting with water or other polar/charged small molecules, hence contributing to dehydration tolerance.