Rice dehydrin K-segments have in vitro antibacterial activity

A YSK-Type Dehydrin from Nicotiana tabacum Enhanced Copper Tolerance in Escherichia coli

Copper is an essential micronutrient for the maintenance of normal cell function but is toxic in excess. Dehydrins are group two late embryogenesis abundant proteins, which facilitate plant survival in harsh environmental conditions. Here, a YSK-type dehydrin, NtDhn17, was cloned from Nicotiana tabacum under copper toxicity and characterized using a heterologous expression system and in vitro or in vivo experiments and exhibited characteristics of intrinsic disorder during in vitro analyses. Heterologous expression of NtDHN17 enhanced the tolerance of E. coli to various metals, osmotic, and oxidative stress. NtDHN17 showed no Cu²⁺-binding properties in vivo or in vitro, indicating that metal ion binding is not universal among dehydrins. In vitro and in vivo experiments suggested that NtDHN17 behaved as a potent anti-aggregation agent providing strong protection to aggregated proteins induced by excess copper ions, an effect dependent on the K-segment but not on the Y- or S-segments. In summary, the protective role of NtDHN17 towards E. coli under conditions of copper toxicity may be related to anti-aggregation ability rather than its acting as an ion scavenger, which might be a valuable target for the genetic improvement of resistance to heavy metal stresses in plants.

AnDHN, a Dehydrin Protein From Ammopiptanthus nanus, Mitigates the Negative Effects of Drought Stress in Plants

Dehydrins (DHNs) play crucial roles in a broad spectrum of abiotic stresses in model plants. However, the evolutionary role of DHNs has not been explored, and the function of DHN proteins is largely unknown in Ammopiptanthus nanus (A. nanus), an ancient and endangered legume species from the deserts of northwestern China. In this study, we isolated a drought-response gene (c195333_g1_i1) from a drought-induced RNA-seq library of A. nanus. Evolutionary bioinformatics showed that c195333_g1_i1 is an ortholog of Arabidopsis DHN, and we renamed it AnDHN. Moreover, DHN proteins may define a class of proteins that are evolutionarily conserved in all angiosperms that have experienced a contraction during the evolution of legumes. Arabidopsis plants overexpressing AnDHN exhibited morpho-physiological changes, such as an increased germination rate, higher relative water content (RWC), higher proline (PRO) content, increased peroxidase (POD) and catalase (CAT) activities, lower contents of malondialdehyde (MDA), H₂O₂ and O₂ ^-, and longer root length. Our results showed that the transgenic lines had improved drought resistance with deep root system architecture, excellent water retention, increased osmotic adjustment, and enhanced reactive oxygen species (ROS) scavenging. Furthermore, the transgenic lines also had enhanced salt and cold tolerance. Our findings demonstrate that AnDHN may be a good candidate gene for improving abiotic stress tolerance in crops. Key Message: Using transcriptome analysis in Ammopiptanthus nanus, we isolated a drought-responsive gene, AnDHN, that plays a key role in enhancing abiotic stress tolerance in plants, with strong functional diversification in legumes.

The forgotten 2S albumin proteins: Importance, structure, and biotechnological application in agriculture and human health

2S albumin proteins are a group of important seed storage proteins (SSPs) essential to seeds at early and late developmental stages, by providing amino acids and other nutrients during germination and for seed defense. 2S albumins possess a well-conserved cysteine supporting the stability of temperature, pH, and proteolysis. The 3D structure rich in alpha-helices and positively charged is particularly suited for antibacterial and antifungal activity, which is presented by many 2S albumins. However, the hypervariable region present in 2S albumins induces allergenic reactions. Because of that, 2S albumins have never been recognized for their biotechnological potential. However, the development of servers used for the rational design of antimicrobial molecules has now brought a new application to 2S albumins, acting as a model to design antimicrobial molecules without the toxic or allergenic effects of 2S albumins. Therefore, this review is focused on discussing the importance of 2S albumins to seed development and defense and the biochemical, structural and functional properties of these proteins thought to play a role in their antimicrobial activity. Additionally, the application of 2S albumins to design synthetic antimicrobial peptides is discussed, potentially bringing new functions to these forgotten proteins.

Different dehydrins perform separate functions in Physcomitrella patens

Dehydrins, PpDHNA and PpDHNB from Physcomitrella patens provide drought and cold tolerance while PpDHNC shows antimicrobial property suggesting different dehydrins perform separate functions in P. patens. The moss Physcomitrella patens can withstand extremes of environmental condition including abiotic stress such as dehydration, salinity, low temperature and biotic stress such as pathogen attack. Osmotic stress is inflicted under both cold and drought stress conditions where dehydrins have been found to play a significant protective role. In this study, a comparative analysis was drawn for the three dehydrins PpDHNA, PpDHNB and PpDHNC from P. patens. Our data shows that PpDHNA and PpDHNB play a major role in cellular protection during osmotic stress. PpDHNB showed several fold upregulation of the gene when P. patens was subjected to cold and osmotic stress in combination. PpDHNA and PpDHNB provide protection to enzyme lactate dehydrogenase under osmotic as well as freezing conditions. PpDHNC possesses antibacterial activity and thus may have a role in biotic stress response. Overexpression of PpDHNA, PpDHNB and PpDHNC in transgenic tobacco showed a better performance for PpDHNB with respect to cold and osmotic stress. These results suggest that specific dehydrins contribute to tolerance of mosses under different stress conditions.

Isolation, cloning, and characterization of a novel Sorghum dehydrin (SbDhn2) protein

Plants can produce their own set of defense molecules in an attempt to survive under stressed conditions. Dehydrins play a considerable role in protecting the plants under varied stress situations. We have isolated a novel SK3 type dehydrin from Sorghum capable of protecting the enzyme lactate dehydrogenase in vitro under both cold and high temperature. This protein showed non-canonical migration in a sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) due to the high hydrophilicity of the protein. The high percentage of glycine and histidine residues present in the protein sequence is responsible for the radical scavenging activity of the protein. The protein also exhibited binding affinity to metal ions owing to the histidine-rich motifs, therefore chelating the metal ions and making them unavailable to systems responsible for generation of reactive oxygen species (ROS). In the presence of specific metal ions, the protein showed reversible aggregation with certain degree of protease resistivity along with induction of secondary structures. The resistivity of the protein to degradation might be implicated in stress situations, thus leading to an increase in the shelf life of the protein. Association with metal ions like copper and zinc at a fairly low concentration increased the protective effect of the SbDHN2 protein for lactate dehydrogenase (LDH) activity to a considerable extent. The synthesis of this dehydrin in stressed plants might help the plant in rendering stress tolerance.

Wheat dehydrin K-segments ensure bacterial stress tolerance, antiaggregation and antimicrobial effects

Dehydrins are a group of plant proteins that have been shown to be involved in the tolerance of various abiotic stresses such as dehydration, salinity, and low temperature. We have previously shown that the K-segments of the wheat dehydrin DHN-5 are essential for the protection of enzyme activities in vitro. In this study, we further investigate the role of the K-segments in the growth of Escherichia coli under various stresses, and we tested their antibacterial and antifungal activities. Our results showed that the truncated forms of DHN-5 containing the two K-segments enhanced tolerance of E. coli against diverse stresses by protecting proteins against aggregation. In addition, we demonstrated that the K-segments have antibacterial and antifungal activities against Gram-positive and Gram-negative bacteria and fungi. Based on these results, we propose that the K-segments may play a protective role in plants not only under abiotic stress conditions but also most likely during defense mechanisms.

Novel dehydrins lacking complete K-segments in Pinaceae. The exception rather than the rule

Dehydrins are thought to play an essential role in the plant response, acclimation and tolerance to different abiotic stresses, such as cold and drought. These proteins contain conserved and repeated segments in their amino acid sequence, used for their classification. Thus, dehydrins from angiosperms present different repetitions of the segments Y, S, and K, while gymnosperm dehydrins show A, E, S, and K segments. The only fragment present in all the dehydrins described to date is the K-segment. Different works suggest the K-segment is involved in key protective functions during dehydration stress, mainly stabilizing membranes. In this work, we describe for the first time two Pinus pinaster proteins with truncated K-segments and a third one completely lacking K-segments, but whose sequence homology leads us to consider them still as dehydrins. qRT-PCR expression analysis show a significant induction of these dehydrins during a severe and prolonged drought stress. By in silico analysis we confirmed the presence of these dehydrins in other Pinaceae species, breaking the convention regarding the compulsory presence of K-segments in these proteins. The way of action of these unusual dehydrins remains unrevealed.

Expression of dehydrin gene from Arctic Cerastium arcticum increases abiotic stress tolerance and enhances the fermentation capacity of a genetically engineered Saccharomyces cerevisiae laboratory strain

We investigated Arctic plants to determine if they have a specific mechanism enabling them to adapt to extreme environments because they are subject to such conditions throughout their life cycles. Among the cell defense systems of the Arctic mouse-ear chickweed Cerastium arcticum, we identified a stress-responsive dehydrin gene CaDHN that belongs to the SK5 subclass and contains conserved regions with one S segment at the N-terminus and five K segments from the N-terminus to the C-terminus. To investigate the molecular properties of CaDHN, the yeast Saccharomyces was transformed with CaDHN. CaDHN-expressing transgenic yeast (TG) cells recovered more rapidly from challenge with exogenous stimuli, including oxidants (hydrogen peroxide, menadione, and tert-butyl hydroperoxide), high salinity, freezing and thawing, and metal (Zn(2+)), than wild-type (WT) cells. TG cells were sensitive to copper, cobalt, and sodium dodecyl sulfate. In addition, the cell survival of TG cells was higher than that of WT cells when cells at the mid-log and stationary stages were exposed to increased ethanol concentrations. There was a significant difference in cultures that have an ethanol content >16 %. During glucose-based batch fermentation at generally used (30 °C) and low (18 °C) temperatures, TG cells produced a higher alcohol concentration through improved cell survival. Specifically, the final alcohol concentrations were 13.3 and 13.2 % in TG cells during fermentation at 30 and 18 °C, respectively, whereas they were 10.2 and 9.4 %, respectively, in WT cells under the same fermentation conditions. An in vitro assay revealed that purified CaDHN acted as a reactive oxygen species scavenger by neutralizing H2O2 and a chaperone by preventing high temperature-mediated catalase inactivation. Taken together, our results show that CaDHN expression in transgenic yeast confers tolerance to various abiotic stresses by improving redox homeostasis and enhances fermentation capacity, especially at low temperatures (18 °C).

Plant dehydrins and stress tolerance: versatile proteins for complex mechanisms

Dehydrins (DHNs), or group 2 LEA (Late Embryogenesis Abundant) proteins, play a fundamental role in plant response and adaptation to abiotic stresses. They accumulate typically in maturing seeds or are induced in vegetative tissues following salinity, dehydration, cold, and freezing stress. The generally accepted classification of dehydrins is based on their structural features, such as the presence of conserved sequences, designated as Y, S, and K segments. The K segment representing a highly conserved 15 amino acid motif forming amphiphilic α-helix is especially important since it has been found in all dehydrins. Since more than 20 years, they are thought to play an important protective role during cellular dehydration but their precise function remains unclear. This review outlines the current status of the progress made towards the structural, physico-chemical and functional characterization of plant dehydrins and how these features could be exploited in improving stress tolerance in plants.