Group 1 LEA proteins, an ancestral plant protein group, are also present in other eukaryotes, and in the archeae and bacteria domains

Genome-wide analysis and functional validation reveal the role of late embryogenesis abundant genes in strawberry (Fragaria × ananassa) fruit ripening

BACKGROUND

Late embryogenesis abundant (LEA) proteins play important roles in plant growth and development, as well as stresses responsiveness. Nowadays, it has been found that LEAs also have function in fruit ripening. However, the comprehensive analysis on a genome-wide basis of LEA family remains limited, and the role of LEA in fruit ripening has not been fully explored yet, especially in strawberry, an economic important plant and ideal material for studying fruit ripening.

RESULTS

In this study, a total of 266 putative LEA proteins were identified and characterized in strawberry genome. Subcellular localization prediction indicated that they were mostly localized in chloroplast, cytoplasm and nucleus. Duplication events detection revealed that whole genome duplication or segmental was the main driver for the expansion of LEA family in strawberry. The phylogenetic analysis suggested that FaLEAs were classified into eight groups, among which, LEA2 was the largest subgroup with 179 members, followed by LEA3, dehydrin (DHN), LEA4 and SMP (seed maturation protein). The LEA1 and DHN groups were speculated to play dominant roles in strawberry fruit development and ripening, according to their larger proportion of members detected as differentially expressed genes during such process. Notably, the expression of FaLEA167 belonging to LEA1 group was altered by strawberry maturation, and inhibited by overexpression of negative regulators of ripening (a cytosolic/plastid glyceraldehyde-3-phosphate dehydrogenase, FaGAPC2 and a cytosolic pyruvate kinase, FaPKc2.2). Subsequently, overexpression of FaLEA167 significantly increased the percentage of fruit at green stage, while reduced the full red fruit proportion. In consistent, the anthocyanins content and the fruit skin color variable reflecting a range from greenness to redness (a* value) were significantly reduced. Whereas, FaLEA167 overexpression apparently up-regulated citric acid, soluble protein and malondialdehyde content, but had no obvious effects on total soluble solids, sugar, flavonoids, phenolics content and antioxidant capacity.

CONCLUSIONS

These findings not only provided basic information of FaLEA family for further functional research, but also revealed the involvement of FaLEA167 in negatively regulating strawberry fruit ripening, giving new insights into understanding of FaLEA functions.

Late Embryogenesis Abundant Proteins Contribute to the Resistance of Toxoplasma gondii Oocysts against Environmental Stresses

Toxoplasma gondii oocysts, which are shed in large quantities in the feces from infected felines, are very stable in the environment, resistant to most inactivation procedures, and highly infectious. The oocyst wall provides an important physical barrier for sporozoites contained inside oocysts, protecting them from many chemical and physical stressors, including most inactivation procedures. Furthermore, sporozoites can withstand large temperature changes, even freeze-thawing, as well as desiccation, high salinity, and other environmental insults; however, the genetic basis for this environmental resistance is unknown. Here, we show that a cluster of four genes encoding Late Embryogenesis Abundant (LEA)-related proteins are required to provide Toxoplasma sporozoites resistance to environmental stresses. Toxoplasma LEA-like genes (TgLEAs) exhibit the characteristic features of intrinsically disordered proteins, explaining some of their properties. Our in vitro biochemical experiments using recombinant TgLEA proteins show that they have cryoprotective effects on the oocyst-resident lactate dehydrogenase enzyme and that induced expression in E. coli of two of them leads to better survival after cold stress. Oocysts from a strain in which the four LEA genes were knocked out en bloc were significantly more susceptible to high salinity, freezing, and desiccation compared to wild-type oocysts. We discuss the evolutionary acquisition of LEA-like genes in Toxoplasma and other oocyst-producing apicomplexan parasites of the Sarcocystidae family and discuss how this has likely contributed to the ability of sporozoites within oocysts to survive outside the host for extended periods. Collectively, our data provide a first molecular detailed view on a mechanism that contributes to the remarkable resilience of oocysts against environmental stresses. IMPORTANCE Toxoplasma gondii oocysts are highly infectious and may survive in the environment for years. Their resistance against disinfectants and irradiation has been attributed to the oocyst and sporocyst walls by acting as physical and permeability barriers. However, the genetic basis for their resistance against stressors like changes in temperature, salinity, or humidity, is unknown. We show that a cluster of four genes encoding Toxoplasma Late Embryogenesis Abundant (TgLEA)-related proteins are important for this resistance to environmental stresses. TgLEAs have features of intrinsically disordered proteins, explaining some of their properties. Recombinant TgLEA proteins show cryoprotective effects on the parasite's lactate dehydrogenase, an abundant enzyme in oocysts, and expression in E. coli of two TgLEAs has a beneficial effect on growth after cold stress. Moreover, oocysts from a strain lacking all four TgLEA genes were more susceptible to high salinity, freezing, and desiccation compared to wild-type oocysts, highlighting the importance of the four TgLEAs for oocyst resilience.

A simple method to purify intrinsically disordered proteins by adjusting trichloroacetic acid concentration

Late embryogenic abundant proteins (LEA) are a group of proteins that accumulate during the desiccation phase of the seed and in response to water deficit in the plant. Most LEA proteins are highly hydrophilic and have physicochemical characteristics similar to those of intrinsically disordered proteins (IDPs). Although the function of LEA proteins is not fully understood, there is evidence indicating that these proteins have an important role in reducing the effects caused by water limitation. The analysis of the biochemical and physicochemical characteristics of LEA proteins is crucial to determine their function, for which it is necessary to obtain large amounts of pure protein. Within this current work, we have improved our previous TCA purification method used for basic recombinant LEA proteins to obtain acidic IDPs, the method reported here is fast and simple and is based on the enrichment of the protein of interest by boiling of the bacterial extract followed by a precipitation with different concentrations of TCA and salt. This protocol was applied to acidic and basic IDPs, represented by eight recombinant LEAs, resulting in milligram quantities of highly enriched proteins, which keep their in vitro functionality.

LEAfing through literature: late embryogenesis abundant proteins coming of age-achievements and perspectives

To deal with increasingly severe periods of dehydration related to global climate change, it becomes increasingly important to understand the complex strategies many organisms have developed to cope with dehydration and desiccation. While it is undisputed that late embryogenesis abundant (LEA) proteins play a key role in the tolerance of plants and many anhydrobiotic organisms to water limitation, the molecular mechanisms are not well understood. In this review, we summarize current knowledge of the physiological roles of LEA proteins and discuss their potential molecular functions. As these are ultimately linked to conformational changes in the presence of binding partners, post-translational modifications, or water deprivation, we provide a detailed summary of current knowledge on the structure-function relationship of LEA proteins, including their disordered state in solution, coil to helix transitions, self-assembly, and their recently discovered ability to undergo liquid-liquid phase separation. We point out the promising potential of LEA proteins in biotechnological and agronomic applications, and summarize recent advances. We identify the most relevant open questions and discuss major challenges in establishing a solid understanding of how these intriguing molecules accomplish their tasks as cellular sentinels at the limits of surviving water scarcity.

Evaluation of a bacterial group 1 LEA protein as an enzyme protectant from stress-induced inactivation

Late embryogenesis abundant (LEA) proteins are hydrophilic proteins that lack a well-ordered tertiary structure and accumulate to high levels in response to water deficit, in organisms such as plants, fungi, and bacteria. The mechanisms proposed to protect cellular structures and enzymes are water replacement, ion sequestering, and membrane stabilization. The activity of some proteins has a limited shelf-life due to instability that can be caused by their structure or the presence of a stress condition that limits their activity; several LEA proteins have been shown to behave as cryoprotectants in vitro. Here, we report a group1 LEA from Azotobacter vinelandii AvLEA1, capable of conferring protection to lactate dehydrogenase, catechol dioxygenase, and Baylase peroxidase against freeze-thaw treatments, desiccation, and oxidative damage, making AvLEA a promising biological stabilizer reagent. This is the first evidence of protection provided by this LEA on enzymes with biotechnological potential, such as dioxygenase and peroxidase under in vitro stress conditions. Our results suggest that AvLEA could act as a molecular chaperone, or a "molecular shield," preventing either dissociation or antiaggregation, or as a radical scavenger, thus preventing damage to these target enzymes during induced stress. KEY POINTS: • This work expands the basic knowledge of the less-known bacterial LEA proteins and their in vitro protection potential. • AvLEA is a bacterial protein that confers in vitro protection to three enzymes with different characteristics and oligomeric arrangement. • The use of AvLEA as a stabilizer agent could be further explored using dioxygenase and peroxidase in bioremediation treatments. AvLEA1 protects against freeze-thaw treatments, desiccation, and oxidative damage on three different enzymes with biotechnological potential.

Examples of Extreme Survival: Tardigrade Genomics and Molecular Anhydrobiology

Tardigrades are ubiquitous meiofauna that are especially renowned for their exceptional extremotolerance to various adverse environments, including pressure, temperature, and even ionizing radiation. This is achieved through a reversible halt of metabolism triggered by desiccation, a phenomenon called anhydrobiosis. Recent establishment of genome resources for two tardigrades, Hypsibius exemplaris and Ramazzottius varieornatus, accelerated research to uncover the molecular mechanisms behind anhydrobiosis, leading to the discovery of many tardigrade-unique proteins. This review focuses on the history, methods, discoveries, and current state and challenges regarding tardigrade genomics, with an emphasis on molecular anhydrobiology. Remaining questions and future perspectives regarding prospective approaches to fully elucidate the molecular machinery of this complex phenomenon are discussed.

LEA motifs promote desiccation tolerance in vivo

BACKGROUND

Cells and organisms typically cannot survive in the absence of water. However, some animals including nematodes, tardigrades, rotifers, and some arthropods are able to survive near-complete desiccation. One class of proteins known to play a role in desiccation tolerance is the late embryogenesis abundant (LEA) proteins. These largely disordered proteins protect plants and animals from desiccation. A multitude of studies have characterized stress-protective capabilities of LEA proteins in vitro and in heterologous systems. However, the extent to which LEA proteins exhibit such functions in vivo, in their native contexts in animals, is unclear. Furthermore, little is known about the distribution of LEA proteins in multicellular organisms or tissue-specific requirements in conferring stress protection. Here, we used the nematode C. elegans as a model to study the endogenous function of an LEA protein in an animal.

RESULTS

We created a null mutant of C. elegans LEA-1, as well as endogenous fluorescent reporters of the protein. LEA-1 mutant animals formed defective dauer larvae at high temperature. We confirmed that C. elegans lacking LEA-1 are sensitive to desiccation. LEA-1 mutants were also sensitive to heat and osmotic stress and were prone to protein aggregation. During desiccation, LEA-1 expression increased and became more widespread throughout the body. LEA-1 was required at high levels in body wall muscle for animals to survive desiccation and osmotic stress, but expression in body wall muscle alone was not sufficient for stress resistance, indicating a likely requirement in multiple tissues. We identified minimal motifs within C. elegans LEA-1 that were sufficient to increase desiccation survival of E. coli. To test whether such motifs are central to LEA-1's in vivo functions, we then replaced the sequence of lea-1 with these minimal motifs and found that C. elegans dauer larvae formed normally and survived osmotic stress and mild desiccation at the same levels as worms with the full-length protein.

CONCLUSIONS

Our results provide insights into the endogenous functions and expression dynamics of an LEA protein in a multicellular animal. The results show that LEA-1 buffers animals from a broad range of stresses. Our identification of LEA motifs that can function in both bacteria and in a multicellular organism in vivo suggests the possibility of engineering LEA-1-derived peptides for optimized desiccation protection.

Subcellular Localization of Seed-Expressed LEA_4 Proteins Reveals Liquid-Liquid Phase Separation for LEA9 and for LEA48 Homo- and LEA42-LEA48 Heterodimers

LEA proteins are involved in plant stress tolerance. In Arabidopsis, the LEA_4 Pfam group is the biggest group with the majority of its members being expressed in dry seeds. To assess subcellular localization in vivo, we investigated 11 seed-expressed LEA_4 proteins in embryos dissected from dry seeds expressing LEA_4 fusion proteins under its native promoters with the Venus fluorescent protein (proLEA_4::LEA_4:Venus). LEA_4 proteins were shown to be localized in the endoplasmic reticulum, nucleus, mitochondria, and plastids. LEA9, in addition to the nucleus, was also found in cytoplasmic condensates in dry seeds dependent on cellular hydration level. Most investigated LEA_4 proteins were detected in 4-d-old seedlings. In addition, we assessed bioinformatic tools for predicting subcellular localization and promoter motifs of 11 seed-expressed LEA_4 proteins. Ratiometric bimolecular fluorescence complementation assays showed that LEA7, LEA29, and LEA48 form homodimers while heterodimers were formed between LEA7-LEA29 and LEA42-LEA48 in tobacco leaves. Interestingly, LEA48 homodimers and LEA42-LEA48 heterodimers formed droplets structures with liquid-like behavior. These structures, along with LEA9 cytoplasmic condensates, may have been formed through liquid-liquid phase separation. These findings suggest possible important roles of LLPS for LEA protein functions.

Multiomics study of a heterotardigrade, Echinisicus testudo, suggests the possibility of convergent evolution of abundant heat-soluble proteins in Tardigrada

Background

Many limno-terrestrial tardigrades can enter an ametabolic state, known as anhydrobiosis, upon desiccation, in which the animals can withstand extreme environments. Through genomics studies, molecular components of anhydrobiosis are beginning to be elucidated, such as the expansion of oxidative stress response genes, loss of stress signaling pathways, and gain of tardigrade-specific heat-soluble protein families designated CAHS and SAHS. However, to date, studies have predominantly investigated the class Eutardigrada, and molecular mechanisms in the remaining class, Heterotardigrada, still remains elusive. To address this gap in the research, we report a multiomics study of the heterotardigrade Echiniscus testudo, one of the most desiccation-tolerant species which is not yet culturable in laboratory conditions.

Results

In order to elucidate the molecular basis of anhydrobiosis in E. testudo, we employed a multi-omics strategy encompassing genome sequencing, differential transcriptomics, and proteomics. Using ultra-low input library sequencing protocol from a single specimen, we sequenced and assembled the 153.7 Mbp genome annotated using RNA-Seq data. None of the previously identified tardigrade-specific abundant heat-soluble genes was conserved, while the loss and expansion of existing pathways were partly shared. Furthermore, we identified two families novel abundant heat-soluble proteins, which we named E. testudo Abundant Heat Soluble (EtAHS), that are predicted to contain large stretches of disordered regions. Likewise the AHS families in eutardigrada, EtAHS shows structural changes from random coil to alphahelix as the water content was decreased in vitro. These characteristics of EtAHS proteins are analogous to those of CAHS in eutardigrades, while there is no conservation at the sequence level.

Conclusions

Our results suggest that Heterotardigrada have partly shared but distinct anhydrobiosis machinery compared with Eutardigrada, possibly due to convergent evolution within Tardigrada. (276/350).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08131-x.

Determining the Protective Activity of IDPs Under Partial Dehydration and Freeze-Thaw Conditions

Unlike for structured proteins, the study of intrinsically disordered proteins (IDPs) requires selection of ad hoc assays and strategies to characterize their dynamic structure and function. Late embryogenesis abundant (LEA) proteins are important plant IDPs closely related to water-deficit stress response. Diverse hypothetical functions have been proposed for LEA proteins, such as membrane stabilizers during cold stress, oxidative regulators acting as ion metal binding molecules, and protein protectants during dehydration and cold/freezing conditions. Here we present two detailed protocols to characterize IDPs with potential protein/enzyme protection activity under partial dehydration and freeze-thaw treatments.

The in vitro structure and functions of the disordered late embryogenesis abundant three proteins

Late embryogenesis abundant (LEA) proteins are produced during seed embryogenesis and in vegetative tissue in response to various abiotic stressors. A correlation has been established between LEA expression and stress tolerance, yet their precise biochemical mechanism remains elusive. LEA proteins are very rich in hydrophilic amino acids, and they have been found to be intrinsically disordered proteins (IDPs) in vitro. Here, we perform biochemical and structural analyses of the four LEA3 proteins from Arabidopsis thaliana (AtLEA3). We show that the LEA3 proteins are disordered in solution but have regions with propensity for order. All LEA3 proteins were effective cryoprotectants of LDH in the freeze/thaw assays, while only one member, AtLEA3-4, was shown to bind Cu²⁺ and Fe³⁺ ions with micromolar affinity. As well, only AtLEA3-4 showed binding and a gain in α-helicity in the presence of the membrane mimic dodecylphosphocholine (DPC). We explored this interaction in greater detail using ¹⁵ N-heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance, and demonstrate that two sets of conserved motifs present in AtLEA3-4 are involved in the interaction with the DPC micelles, which themselves gain α-helical structure.

Conserved sequence motifs in the abiotic stress response protein late embryogenesis abundant 3

LEA3 proteins, a family of abiotic stress proteins, are defined by the presence of a tryptophan-containing motif, which we name the W-motif. We use Pfam LEA3 sequences to search the Phytozome database to create a W-motif definition and a LEA3 sequence dataset. A comprehensive analysis of these sequences revealed four N-terminal motifs, as well as two previously undiscovered C-terminal motifs that contain conserved acidic and hydrophobic residues. The general architecture of the LEA3 sequences consisted of an N-terminal motif with a potential mitochondrial transport signal and the twin-arginine motif cut-site, followed by a W-motif and often a C-terminal motif. Analysis of species distribution of the motifs showed that one architecture was found exclusively in Commelinids, while two were distributed fairly evenly over all species. The physiochemical properties of the different architectures showed clustering in a relatively narrow range compared to the previously studied dehydrins. The evolutionary analysis revealed that the different sequences grouped into clades based on architecture, and that there appear to be at least two distinct groups of LEA3 proteins based on their architectures and physiochemical properties. The presence of LEA3 proteins in non-vascular plants but their absence in algae suggests that LEA3 may have arisen in the evolution of land plants.

Characteristics, dynamics and mechanisms of actions of some major stress-induced biomacromolecules; addressing Artemia as an excellent biological model

Stress tolerance is one of the most prominent and interesting topics in biology since many macro- and micro-adaptations have evolved in resistant organisms that are worth studying. When it comes to confronting various environmental stressors, the extremophile Artemia is unrivaled in the animal kingdom. In the present review, the evolved molecular and cellular basis of stress tolerance in resistant biological systems are described, focusing on Artemia cyst as an excellent biological model. The main purpose of the review is to discuss how the structure and physicochemical characteristics of protective factors such as late embryogenesis abundant proteins (LEAPs), small heat shock proteins (sHSPs) and trehalose are related to their functions and by which mechanisms, they exert their functions. In addition, some metabolic depressors in Artemia encysted embryos are also mentioned, indirectly playing important roles in stress tolerance. Importantly, a great deal of attention is given to the LEAPs, exhibiting distinctive folding behaviors and mechanisms of actions. For instance, molecular shield function, chaperone-like activity, moonlighting property, sponging and snorkeling capabilities of the LEAPs are delineated here. Moreover, the molecular interplay between some of these factors is mentioned, leading to their synergistic effects. Interestingly, Artemia life cycle adapts to environmental conditions. Diapause is the defense mode of this life cycle, safeguarding Artemia encysted embryos against various environmental stressors. Communicated by Ramaswamy H. Sarma.

Shared up-regulation and contrasting down-regulation of gene expression distinguish desiccation-tolerant from intolerant green algae

Among green plants, desiccation tolerance is common in seeds and spores but rare in leaves and other vegetative green tissues. Over the last two decades, genes have been identified whose expression is induced by desiccation in diverse, desiccation-tolerant (DT) taxa, including, e.g., late embryogenesis abundant proteins (LEA) and reactive oxygen species scavengers. This up-regulation is observed in DT resurrection plants, mosses, and green algae most closely related to these Embryophytes. Here we test whether this same suite of protective genes is up-regulated during desiccation in even more distantly related DT green algae, and, importantly, whether that up-regulation is unique to DT algae or also occurs in a desiccation-intolerant relative. We used three closely related aquatic and desert-derived green microalgae in the family Scenedesmaceae and capitalized on extraordinary desiccation tolerance in two of the species, contrasting with desiccation intolerance in the third. We found that during desiccation, all three species increased expression of common protective genes. The feature distinguishing gene expression in DT algae, however, was extensive down-regulation of gene expression associated with diverse metabolic processes during the desiccation time course, suggesting a switch from active growth to energy-saving metabolism. This widespread downshift did not occur in the desiccation-intolerant taxon. These results show that desiccation-induced up-regulation of expression of protective genes may be necessary but is not sufficient to confer desiccation tolerance. The data also suggest that desiccation tolerance may require induced protective mechanisms operating in concert with massive down-regulation of gene expression controlling numerous other aspects of metabolism.

Transcriptomic and metabolomic analyses reveal mechanisms of adaptation to salinity in which carbon and nitrogen metabolism is altered in sugar beet roots

BACKGROUND

Beta vulgaris L. is one of the main sugar-producing crop species and is highly adaptable to saline soil. This study explored the alterations to the carbon and nitrogen metabolism mechanisms enabling the roots of sugar beet seedlings to adapt to salinity.

RESULTS

The ionome, metabolome, and transcriptome of the roots of sugar beet seedlings were evaluated after 1 day (short term) and 7 days (long term) of 300 mM Na+ treatment. Salt stress caused reactive oxygen species (ROS) damage and ion toxicity in the roots. Interestingly, under salt stress, the increase in the Na+/K+ ratio compared to the control ratio on day 7 was lower than that on day 1 in the roots. The transcriptomic results showed that a large number of differentially expressed genes (DEGs) were enriched in various metabolic pathways. A total of 1279 and 903 DEGs were identified on days 1 and 7, respectively, and were mapped mainly to 10 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Most of the genes were involved in carbon metabolism and amino acid (AA) biosynthesis. Furthermore, metabolomic analysis revealed that sucrose metabolism and the activity of the tricarboxylic acid (TCA) cycle increased in response to salt stress. After 1 day of stress, the content of sucrose decreased, whereas the content of organic acids (OAs) such as L-malic acid and 2-oxoglutaric acid increased. After 7 days of salt stress, nitrogen-containing metabolites such as AAs, betaine, melatonin, and (S)-2-aminobutyric acid increased significantly. In addition, multiomic analysis revealed that the expression of the gene encoding xanthine dehydrogenase (XDH) was upregulated and that the expression of the gene encoding allantoinase (ALN) was significantly downregulated, resulting in a large accumulation of allantoin. Correlation analysis revealed that most genes were significantly related to only allantoin and xanthosine.

CONCLUSIONS

Our study demonstrated that carbon and nitrogen metabolism was altered in the roots of sugar beet plants under salt stress. Nitrogen metabolism plays a major role in the late stages of salt stress. Allantoin, which is involved in the purine metabolic pathway, may be a key regulator of sugar beet salt tolerance.

The functional diversity of structural disorder in plant proteins

Structural disorder in proteins is a widespread feature distributed in all domains of life, particularly abundant in eukaryotes, including plants. In these organisms, intrinsically disordered proteins (IDPs) perform a diversity of functions, participating as integrators of signaling networks, in transcriptional and post-transcriptional regulation, in metabolic control, in stress responses and in the formation of biomolecular condensates by liquid-liquid phase separation. Their roles impact the perception, propagation and control of various developmental and environmental cues, as well as the plant defense against abiotic and biotic adverse conditions. In this review, we focus on primary processes to exhibit a broad perspective of the relevance of IDPs in plant cell functions. The information here might help to incorporate this knowledge into a more dynamic view of plant cells, as well as open more questions and promote new ideas for a better understanding of plant life.

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.

Phenotypic characteristics and transcriptome profile of Cryptococcus gattii biofilm

In this study, we characterized Cryptococcus gattii biofilm formation in vitro. There was an increase in the density of metabolically active sessile cells up to 72 h of biofilm formation on polystyrene and glass surfaces. Scanning electron microscopy and confocal laser scanning microscopy analysis revealed that in the early stage of biofilm formation, yeast cells adhered to the abiotic surface as a monolayer. After 12 h, extracellular fibrils were observed projecting from C. gattii cells, connecting the yeast cells to each other and to the abiotic surface; mature biofilm consisted of a dense network of cells deeply encased in an extracellular polymeric matrix. These features were also observed in biofilms formed on polyvinyl chloride and silicone catheter surfaces. We used RNA-Seq-based transcriptome analysis to identify changes in gene expression associated with C. gattii biofilm at 48 h compared to the free-floating planktonic cells. Differential expression analysis showed that 97 and 224 transcripts were up-regulated and down-regulated in biofilm, respectively. Among the biological processes, the highest enriched term showed that the transcripts were associated with cellular metabolic processes, macromolecule biosynthetic processes and translation.

The Pepper Late Embryogenesis Abundant Protein, CaDIL1, Positively Regulates Drought Tolerance and ABA Signaling

Plants as sessile organisms constantly respond to environmental stress during their growth and development. The regulation of transpiration via stomata plays crucial roles in plant adaptation to drought stress. Many enzyme-encoding genes are involved in regulation of transpiration via modulating stomatal opening and closure. Here, we demonstrate that Capsicum annuum Drought Induced Late embryogenesis abundant protein 1 (CaDIL1) gene is a critical regulator of transpirational water loss in pepper. The expression of CaDIL1 in pepper leaves was upregulated after exposure to abscisic acid (ABA) and drought. Phenotype analysis showed that CaDIL1-silenced pepper and CaDIL1-overexpressing (OX) Arabidopsis transgenic plants exhibited reduced and enhanced drought tolerance, respectively, accompanied by an altered water loss. Furthermore, ABA sensitivity was significantly lower in CaDIL1-silenced pepper, but higher in CaDIL1-OX plants, than that in control plants, which resulted in opposite responses to drought stress in these two plant types. Collectively, our data suggest that CaDIL1 positively regulates the ABA signaling and drought stress tolerance.

Ectoine: a compatible solute in radio-halophilic Stenotrophomonas sp. WMA-LM19 strain to prevent ultraviolet-induced protein damage

AIM

Thiss study was conducted to investigate the possible role of a compatible solute from radio-halophilic bacterium against desiccation and ultra-violet radiation-induced oxidative stress.

METHODS AND RESULTS

Nine different radio-resistant bacteria were isolated from desert soil, where strain WMA-LM19 was chosen for detailed studies on the basis of its high tolerance to ultraviolet radiation among all these isolates. Here, 16S rRNA gene sequencing indicated the bacterium was closely related to Stenotrophomonas sp. (KT008383). A bacterial milking strategy was applied for extraction of intracellular compatible solutes in 70% (v/v) ethanol, which were purified by High Performance Liquid Chromatography (HPLC). The compound was characterized as ectoine by ¹ H and ¹³ C Nuclear Magnetic Resonance (NMR), and Mass Spectrometry (MS). Ectoine inhibited oxidative damage to proteins and lipids in comparison to the standard ascorbic acid. It also demonstrated more efficient prevention (54·80%) against lysis to erythrocytes membrane by surface active agents than lecithin. Furthermore, a high level of ectoine-mediated protection of bovine serum albumin against ionizing radiation (1 500-2 000Jm^-2 ) was observed, as indicated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis.

CONCLUSION

The results indicated that ectoine from Stenotrophomonas sp. WMA-LM19 can be used as a potential mitigator and radio-protective agent to overcome radiation- and salinity-mediated oxidative damages in extreme environment.

SIGNIFICANCE AND IMPACT OF THE STUDY

Due to its anti-oxidant properties, ectoine from a radio-halophilic bacterium might be used in sunscreen formulation for protection against UV-induced oxidative stress.

Comparative transcriptomic analysis of the roots of intercropped peanut and maize reveals novel insights into peanut iron nutrition

Intercropping is a vital technology in resource-limited agricultural systems with low inputs. Peanut/maize intercropping enhances iron (Fe) nutrition in calcareous soil. In this study, the transcriptome of peanut and maize roots was analyzed by suppression subtractive hybridization (SSH) and microarray analysis separately. We constructed four SSH libraries using the cDNA of peanut roots based on two cropping patterns: monocropping and intercropping, and two growth stages: vegetative stage and reproductive stage. Lib M1, I1, M2 and I2 comprised 53, 51, 37 and 54 genes, respectively. Six and four transporters were found in the two intercropping-specific SSH libraries, which may facilitate Fe acquisition and protoplasmic homeostasis of metal ions and anions. Specifically, AhNARMP1 and MTP may play a role in boosting Fe nutrition during the vegetative stage. The expression of MYC2 was also upregulated by intercropping, while an ethylene-responsive transcription factor was downregulated during two growth periods. Microarrays indicated that homocysteine S-methyltransferase and serine acetyltransferase 1 upregulated in intercropped maize roots, which directly associated with methionine biosynthesis. It may account for the enhanced phytosiderophore released capacity in intercropping, which benefited the Fe nutrition of intercropped peanut in reproductive stage. Two aminocyclopropane-1-carboxylic acid synthase oxidase genes, which are related to ethylene biosynthesis, were downregulated in maize root by intercropping. Taken together with our previous proteomic work, the results indicated that intercropping enhances jasmonate signaling and weakens ethylene signaling in peanut and maize roots, which may improve ecological adaptation of the peanut plant to intercropping systems.

An Atypical Late Embryogenesis Abundant Protein OsLEA5 Plays a Positive Role in ABA-Induced Antioxidant Defense in Oryza sativa L

OsLEA5 acts as a co-regulator of a transcriptional fact ZFP36 to enhance the expression and the activity of ascorbate peroxidase OsAPX1 to regulate seed germination in rice, but it it unknown whether OsLEA5 is also crucial in plant seedlings under stress conditions. To determine this, we generated OsLEA5 overexpression and knockdown rice plants. We found that overexpression of OsLEA5 in rice plants enhanced the tolerance to drought and salt stress; in contrast, an RNA interference (RNAi) mutant of OsLEA5 rice plants was more sensitive to drought and salinity. Further investigation found that various stimuli and ABA could induce OsLEA5 expression, and OsLEA5 acted downstream of ZFP36 to be involved in ABA-induced generation of hydrogen peroxide (H2O2), and the regulation of the expression and the activities of antioxidant defense enzymes in plants leaves, and OsLEA5 contributed to stabilize ZFP36. Additionally, OsLEA5 participates in the accumulation of ABA by up-regulating ABA biosynthesis genes and down-regulating ABA metabolism genes. Moreover, we found that two homologs of OsLEA5 (5C700, short for Os05g0526700; and 5C300, short for Os05g0584300) which were induced by ABA also interacted with ZFP36 separately; interestingly, the nuclear-located 5C700 could also act as a co-activator of ZFP36 to modulate OsAPX1, while 5C300 which was down-regulated by ABA induction acted as an ABA-induced inhibitor of ZFP36 to regulate OsAPX1. Hence, our conclusion is that OsLEA5 participates in the ABA-mediated antioxidant defense to function in drought and salt stress response in rice, and the 5C subgroup of LEAs contribute by acting as co-regulators of the transcription factor ZFP36.

Characterization of the late embryogenesis abundant (LEA) proteins family and their role in drought stress tolerance in upland cotton

Background

Late embryogenesis abundant (LEA) proteins are large groups of hydrophilic proteins with major role in drought and other abiotic stresses tolerance in plants. In-depth study and characterization of LEA protein families have been carried out in other plants, but not in upland cotton. The main aim of this research work was to characterize the late embryogenesis abundant (LEA) protein families and to carry out gene expression analysis to determine their potential role in drought stress tolerance in upland cotton. Increased cotton production in the face of declining precipitation and availability of fresh water for agriculture use is the focus for breeders, cotton being the backbone of textile industries and a cash crop for many countries globally.

Results

In this work, a total of 242, 136 and 142 LEA genes were identified in G. hirsutum, G. arboreum and G. raimondii respectively. The identified genes were classified into eight groups based on their conserved domain and phylogenetic tree analysis. LEA 2 were the most abundant, this could be attributed to their hydrophobic character. Upland cotton LEA genes have fewer introns and are distributed in all chromosomes. Majority of the duplicated LEA genes were segmental. Syntenic analysis showed that greater percentages of LEA genes are conserved. Segmental gene duplication played a key role in the expansion of LEA genes. Sixty three miRNAs were found to target 89 genes, such as miR164, ghr-miR394 among others. Gene ontology analysis revealed that LEA genes are involved in desiccation and defense responses. Almost all the LEA genes in their promoters contained ABRE, MBS, W-Box and TAC-elements, functionally known to be involved in drought stress and other stress responses. Majority of the LEA genes were involved in secretory pathways. Expression profile analysis indicated that most of the LEA genes were highly expressed in drought tolerant cultivars Gossypium tomentosum as opposed to drought susceptible, G. hirsutum. The tolerant genotypes have a greater ability to modulate genes under drought stress than the more susceptible upland cotton cultivars.

Conclusion

The finding provides comprehensive information on LEA genes in upland cotton, G. hirsutum and possible function in plants under drought stress.

Electronic supplementary material

The online version of this article (10.1186/s12863-017-0596-1) contains supplementary material, which is available to authorized users.

Characterization of the late embryogenesis abundant (LEA) proteins family and their role in drought stress tolerance in upland cotton

BACKGROUND

Late embryogenesis abundant (LEA) proteins are large groups of hydrophilic proteins with major role in drought and other abiotic stresses tolerance in plants. In-depth study and characterization of LEA protein families have been carried out in other plants, but not in upland cotton. The main aim of this research work was to characterize the late embryogenesis abundant (LEA) protein families and to carry out gene expression analysis to determine their potential role in drought stress tolerance in upland cotton. Increased cotton production in the face of declining precipitation and availability of fresh water for agriculture use is the focus for breeders, cotton being the backbone of textile industries and a cash crop for many countries globally.

RESULTS

In this work, a total of 242, 136 and 142 LEA genes were identified in G. hirsutum, G. arboreum and G. raimondii respectively. The identified genes were classified into eight groups based on their conserved domain and phylogenetic tree analysis. LEA 2 were the most abundant, this could be attributed to their hydrophobic character. Upland cotton LEA genes have fewer introns and are distributed in all chromosomes. Majority of the duplicated LEA genes were segmental. Syntenic analysis showed that greater percentages of LEA genes are conserved. Segmental gene duplication played a key role in the expansion of LEA genes. Sixty three miRNAs were found to target 89 genes, such as miR164, ghr-miR394 among others. Gene ontology analysis revealed that LEA genes are involved in desiccation and defense responses. Almost all the LEA genes in their promoters contained ABRE, MBS, W-Box and TAC-elements, functionally known to be involved in drought stress and other stress responses. Majority of the LEA genes were involved in secretory pathways. Expression profile analysis indicated that most of the LEA genes were highly expressed in drought tolerant cultivars Gossypium tomentosum as opposed to drought susceptible, G. hirsutum. The tolerant genotypes have a greater ability to modulate genes under drought stress than the more susceptible upland cotton cultivars.

CONCLUSION

The finding provides comprehensive information on LEA genes in upland cotton, G. hirsutum and possible function in plants under drought stress.

The ascorbate peroxidase APX1 is a direct target of a zinc finger transcription factor ZFP36 and a late embryogenesis abundant protein OsLEA5 interacts with ZFP36 to co-regulate OsAPX1 in seed germination in rice

Seed germination is a vital developmental process. Abscisic acid (ABA) is an essential repressor of seed germination, while ROS (reactive oxygen species) also plays a vital role in regulating seed germination. ABA could inhibit the production of ROS in seed germination, but the mechanism of ABA reduced ROS production in seed germination was hitherto unknown. Here, by ChIP (chromatin immunoprecipitation)-seq, we found that ZFP36, a rice zinc finger transcription factor, could directly bind to the promoter of OsAPX1, coding an ascorbate peroxidase (APX) which has the most affinity for H₂O₂ (substrate; a type of ROS), and act as a transcriptional activator of OsAPX1 promoter. Moreover, ZFP36 could interact with a late embryogenesis abundant protein OsLEA5 to co-regulate the promoter activity of OsAPX1. The seed germination is highly inhibited in ZFP36 overexpression plants under ABA treatment, while an RNA interference (RNAi) mutant of OsLEA5 rice seeds were less sensitive to ABA, and exogenous ASC (ascorbate acid) could alleviate the inhibition induced by ABA. Thus, our conclusion is that OsAPX1 is a direct target of ZFP36 and OsLEA5 could interact with ZFP36 to co-regulate ABA-inhibited seed germination by controlling the expression of OsAPX1.

Structural disorder in plant proteins: where plasticity meets sessility

Plants are sessile organisms. This intriguing nature provokes the question of how they survive despite the continual perturbations caused by their constantly changing environment. The large amount of knowledge accumulated to date demonstrates the fascinating dynamic and plastic mechanisms, which underpin the diverse strategies selected in plants in response to the fluctuating environment. This phenotypic plasticity requires an efficient integration of external cues to their growth and developmental programs that can only be achieved through the dynamic and interactive coordination of various signaling networks. Given the versatility of intrinsic structural disorder within proteins, this feature appears as one of the leading characters of such complex functional circuits, critical for plant adaptation and survival in their wild habitats. In this review, we present information of those intrinsically disordered proteins (IDPs) from plants for which their high level of predicted structural disorder has been correlated with a particular function, or where there is experimental evidence linking this structural feature with its protein function. Using examples of plant IDPs involved in the control of cell cycle, metabolism, hormonal signaling and regulation of gene expression, development and responses to stress, we demonstrate the critical importance of IDPs throughout the life of the plant.

DrwH, a novel WHy domain-containing hydrophobic LEA5C protein from Deinococcus radiodurans, protects enzymatic activity under oxidative stress

Water stress and hypersensitive response (WHy) domain is typically found as a component of atypical late embryogenesis abundant (LEA) proteins closely associated with resistance to multiple stresses in numerous organisms. Several putative LEA proteins have been identified in Deinococcus bacteria; however their precise function remains unclear. This work reports the characterization of a Deinococcus-specific gene encoding a novel WHy domain-containing hydrophobic LEA5C protein (named DrwH) in D. radiodurans R1. The expression of the drwH gene was induced by oxidative and salinity stresses. Inactivation of this gene resulted in increased sensitivity to oxidative and salinity stresses as well as reduced activities of antioxidant enzymes. The WHy domain of the DrwH protein differs structurally from that of a previously studied bacterial LEA5C protein, dWHy1, identified as a gene product from an Antarctic desert soil metagenome library. Further analysis indicated that in E. coli, the function of DrwH is related to oxidative stress tolerance, whereas dWHy1 is associated with freezing-thawing stress tolerance. Under oxidative stress induced by H₂O₂, DrwH protected the enzymatic activities of malate dehydrogenase (MDH) and lactate dehydrogenase (LDH). These findings provide new insight into the evolutionary and survival strategies of Deinococcus bacteria under extreme environmental conditions.

Towards water-free biobanks: long-term dry-preservation at room temperature of desiccation-sensitive enzyme luciferase in air-dried insect cells

Desiccation-tolerant cultured cells Pv11 derived from the anhydrobiotic midge embryo endure complete desiccation in an ametabolic state and resume their metabolism after rehydration. These features led us to develop a novel dry preservation technology for enzymes as it was still unclear whether Pv11 cells could preserve an exogenous enzyme in the dry state. This study shows that Pv11 cells protect an exogenous desiccation-sensitive enzyme, luciferase (Luc), preserving the enzymatic activity even after dry storage for 372 days at room temperature. A process including preincubation with trehalose, dehydration, storage, and rehydration allowed Pv11 (Pv11-Luc) cells stably expressing luciferase to survive desiccation and still emit luminescence caused by luciferase after rehydration. Luminescence produced by luciferase in Pv11-Luc cells after rehydration did not significantly decrease in presence of a translation inhibitor, showing that the activity did not derive from de novo enzyme synthesis following the resumption of cell metabolism. These findings indicate that the surviving Pv11 cells almost completely protect luciferase during desiccation. Lacking of the preincubation step resulted in the loss of luciferase activity after rehydration. We showed that preincubation with trehalose associated to induction of desiccation tolerance-related genes in Pv11 cells allowed effective in vivo preservation of enzymes in the dry state.

Group 4 late embryogenesis abundant proteins as a model to study intrinsically disordered proteins in plants

Late Embryogenesis Abundant (LEA) proteins comprise a heterogeneous group of proteins that accumulate to high levels in the dry seed and in vegetative plant tissues under water deficit. We recently reported that group 4 LEA proteins from Arabidopsis thaliana, regardless of their structural disorder prevalent in aqueous solution, are able to fold into α-helix when subjected to water deficit and/or macromolecular crowding environments. Interestingly, the ability to gain structure under water limiting conditions is circumscribed to the N-terminal conserved region. This environment- driven conformational plasticity has a functional impact because the conserved N-terminal region is necessary and sufficient to prevent the inactivation and/or aggregation of reporter enzymes, when they are subjected to partial dehydration or freeze-thaw treatments. In this addendum we present a broader analysis of the data and propose that the mechanism by which group 4 LEA proteins exert their chaperone-like activity occurs via a selection of particular LEA structural conformations favored by water deficit environments. In addition, we include further observations regarding the abundance and conservation of histidine residues in LEA proteins of this group, particularly at the C-terminal variable region, supporting the presence of an additional function in the same polypeptides as metal ion sequesters. The structural characteristics of group 4 LEA proteins together with their conceivable multifunctionality, a widespread feature in Intrinsically Disordered Proteins (IDPs), raises the possibility of using this set of proteins as a model to investigate the structure-function relationship of IDPs in plants.

LEA proteins are involved in cyst desiccation resistance and other abiotic stresses in Azotobacter vinelandii

Late embryogenesis abundant (LEA) proteins constitute a large protein family that is closely associated with resistance to abiotic stresses in multiple organisms and protect cells against drought and other stresses. Azotobacter vinelandii is a soil bacterium that forms desiccation-resistant cysts. This bacterium possesses two genes, here named lea1 and lea2, coding for avLEA1 and avLEA2 proteins, both containing 20-mer motifs characteristic of eukaryotic plant LEA proteins. In this study, we found that disruption of the lea1 gene caused a loss of the cysts' viability after 3 months of desiccation, whereas at 6 months, wild-type or lea2 mutant strain cysts remained viable. Vegetative cells of the lea1 mutant were more sensitive to osmotic stress; cysts developed by this mutant were also more sensitive to high temperatures than cysts or vegetative cells of the wild type or of the lea2 mutant. Expression of lea1 was induced several fold during encystment. In addition, the protective effects of these proteins were assessed in Escherichia coli cells. We found that E. coli cells overexpressing avLEA1 were more tolerant to salt stress than control cells; finally, in vitro analysis showed that avLEA1 protein was able to prevent the freeze thaw-induced inactivation of lactate dehydrogenase. In conclusion, avLEA1 is essential for the survival of A. vinelandii in dry conditions and for protection against hyper-osmolarity, two major stress factors that bacteria must cope with for survival in the environment. This is the first report on the role of bacterial LEA proteins on the resistance of cysts to desiccation.

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.

Influence of osmotic stress on desiccation and irradiation tolerance of (hyper)-thermophilic microorganisms

This study examined the influence of prior salt adaptation on the survival rate of (hyper)-thermophilic bacteria and archaea after desiccation and UV or ionizing irradiation treatment. Survival rates after desiccation of Hydrogenothermus marinus and Archaeoglobus fulgidus increased considerably when the cells were cultivated at higher salt concentrations before drying. By doubling the concentration of NaCl, a 30 times higher survival rate of H. marinus after desiccation was observed. Under salt stress, the compatible solute diglycerol phosphate in A. fulgidus and glucosylglycerate in H. marinus accumulated in the cytoplasm. Several different compatible solutes were added as protectants to A. fulgidus and H. marinus before desiccation treatment. Some of these had similar effects as intracellularly produced compatible solutes. The survival rates of H. marinus and A. fulgidus after exposure to UV-C (254 nm) or ionizing X-ray/gamma radiation were irrespective of the salt-induced synthesis or the addition of compatible solutes.

Hydrophilins in the filamentous fungus Neosartorya fischeri (Aspergillus fischeri) have protective activity against several types of microbial water stress

Hydrophilins are proteins that occur in all domains of life and protect cells and organisms against drought and other stresses. They include most of the late embryogenesis abundant (LEA) proteins and the heat shock protein (HSP) Hsp12. Here, the role of a predicted LEA-like protein (LeamA) and two Hsp12 proteins (Hsp12A and Hsp12B) of Neosartorya fischeri was studied. This filamentous fungus forms ascospores that belong to the most stress-resistant eukaryotic cells described to date. Heterologous expression of LeamA, Hsp12A and Hsp12B resulted in increased tolerance against salt and osmotic stress in Escherichia coli. These proteins were also shown to protect lactate dehydrogenase against dry heat and freeze-thaw cycles in vitro. Deletion of leamA caused diminished viability of sexual ascospores after drought and heat. This is the first report on functionality of Hsp12 and putative LeamA proteins derived from filamentous fungi, and their possible role in N. fischeri ascospore resistance against desiccation, high temperature and osmotic stress is discussed.

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.

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

Oviparously developing embryos of the brine shrimp, Artemia, arrest at gastrulation and are released from females as cysts before entering diapause, a state of dormancy and stress tolerance. Diapause is terminated by an external signal, and growth resumes if conditions are permissible. However, if circumstances are unfavorable, cysts enter quiescence, a dormant stage that continues as long as adverse conditions persist. Artemia embryos in diapause and quiescence are remarkably resistant to environmental and physiological stressors, withstanding desiccation, cold, heat, oxidation, ultraviolet radiation, and years of anoxia at ambient temperature when fully hydrated. Cysts have adapted to stress in several ways; they are surrounded by a rigid cell wall impermeable to most chemical compounds and which functions as a shield against ultraviolet radiation. Artemia cysts contain large amounts of trehalose, a non-reducing sugar thought to preserve membranes and proteins during desiccation by replacing water molecules and/or contributing to vitrification. Late embryogenesis abundant proteins similar to those in seeds and other anhydrobiotic organisms are found in cysts, and they safeguard cell organelles and proteins during desiccation. Artemia cysts contain abundant amounts of p26, a small heat shock protein, and artemin, a ferritin homologue, both ATP-independent molecular chaperones important in stress tolerance. The evidence provided in this review supports the conclusion that it is the interplay of these protective elements that make Artemia one of the most stress tolerant of all metazoan organisms.

A novel bacterial Water Hypersensitivity-like protein shows in vivo protection against cold and freeze damage

Metagenomic library screening, by functional or sequence analysis, has become an established method for the identification of novel genes and gene products, including genetic elements implicated in microbial stress response and adaptation. We have identified, using a sequence-based approach, a fosmid clone from an Antarctic desert soil metagenome library containing a novel gene which codes for a protein homologous to a Water Hypersensitivity domain (WHy). The WHy domain is typically found as a component of specific LEA (Late Embryogenesis Abundant) proteins, particularly the LEA-14 (LEA-8) variants, which occur widely in plants, nematodes, bacteria and archaea and which are typically induced by exposure to stress conditions. The novel WHy-like protein (165 amino acid, 18.6 kDa) exhibits a largely invariant NPN motif at the N-terminus and has high sequence identity to genes identified in Pseudomonas genomes. Expression of this protein in Escherichia coli significantly protected the recombinant host against cold and freeze stress.

A group 6 late embryogenesis abundant protein from common bean is a disordered protein with extended helical structure and oligomer-forming properties

Late embryogenesis-abundant proteins accumulate to high levels in dry seeds. Some of them also accumulate in response to water deficit in vegetative tissues, which leads to a remarkable association between their presence and low water availability conditions. A major sub-group of these proteins, also known as typical LEA proteins, shows high hydrophilicity and a high percentage of glycine and other small amino acid residues, distinctive physicochemical properties that predict a high content of structural disorder. Although all typical LEA proteins share these characteristics, seven groups can be distinguished by sequence similarity, indicating structural and functional diversity among them. Some of these groups have been extensively studied; however, others require a more detailed analysis to advance in their functional understanding. In this work, we report the structural characterization of a group 6 LEA protein from a common bean (Phaseolus vulgaris L.) (PvLEA6) by circular dichroism and nuclear magnetic resonance showing that it is a disordered protein in aqueous solution. Using the same techniques, we show that despite its unstructured nature, the addition of trifluoroethanol exhibited an intrinsic potential in this protein to gain helicity. This property was also promoted by high osmotic potentials or molecular crowding. Furthermore, we demonstrate that PvLEA6 protein is able to form soluble homo-oligomeric complexes that also show high levels of structural disorder. The association between PvLEA6 monomers to form dimers was shown to occur in plant cells by bimolecular fluorescence complementation, pointing to the in vivo functional relevance of this association.

Related to ABA-Insensitive3(ABI3)/Viviparous1 and AtABI5 transcription factor coexpression in cotton enhances drought stress adaptation

Drought tolerance is an important trait being pursued by the agbiotech industry. Abscisic acid (ABA) is a stress hormone that mediates a multitude of processes in growth and development, water use efficiency (WUE) and gene expression during seed development and in response to environmental stresses. Arabidopsis B3-domain transcription factor Related to ABA-Insensitive3 (ABI3)/Viviparous1 (namely AtRAV2) and basic leucine zipper (bZIPs) AtABI5 or AtABF3 transactivated ABA-inducible promoter:GUS reporter expression in a maize mesophyll protoplast transient assay and showed synergies in reporter transactivation when coexpressed. Transgenic cotton (Gossypium hirsutum) expressing AtRAV1/2 and/or AtABI5 showed resistance to imposed drought stress under field and greenhouse conditions and exhibited improved photosynthesis and WUEs associated with absorption through larger root system and greater leaf area. We observed synergy for root biomass accumulation in the greenhouse, intrinsic WUE in the field and drought tolerance in stacked AtRAV and AtABI5 double-transgenic cotton. We assessed AtABI5 and AtRAV1/2 involvement in drought stress adaptations through reactive oxygen species scavenging and osmotic adjustment by marker gene expression in cotton. Deficit irrigation-grown AtRAV1/2 and AtABI5 transgenics had 'less-stressed' molecular and physiological phenotypes under drought, likely due to improved photoassimilation and root and shoot sink strengths and enhanced expression of endogenous GhRAV and genes for antioxidant and osmolyte biosynthesis. Overexpression of bZIP and RAV TFs could impact sustainable cotton agriculture and potentially other crops under limited irrigation conditions.