Inhibition of cryoaggregation of phospholipid liposomes by an Arabidopsis intrinsically disordered dehydrin and its K-segment

Function in disorder: A review on the roles of the disordered dehydrin proteins in conferring stress tolerance

Water scarcity as a result of drought is considered to be among the most common forms of abiotic stress which directly hampers plant health. Such conditions often lead to various interlinked physiological conditions, including oxidative stress resulting from increased ROS levels that in turn, induce membranes dysfunction, leading to disruption in cellular ionic balance, and oxidation of macromolecules. Plants employ several mechanisms to counter these hostile conditions, which help them adapt to such unforgiving environments. Accumulation of specific types of proteins called dehydrins (DHNs) represents one such mechanism of adaptation. DHNs are ubiquitous in distribution and have been reported in different life forms; accumulating under a wide spectrum of stress. An important role of DHNs is to protect and maintain cell's macromolecular structure and function, thereby preserving membrane integrity, stabilizing proteins and nucleic acid, and conferring protection against oxidative stress. The present article explores different aspects of DHNs, including their structural compositions, architectures and conformational flexibility, and their role in combating a plethora of stress environments, with specific focus towards drought. Possible involvements of DHNs in intracellular biocondensates formation through phase separation and their role in stress sensing are also provided.

Dehydrin CaDHN2 Enhances Drought Tolerance by Affecting Ascorbic Acid Synthesis under Drought in Peppers

Peppers (Capsicum annuum L.), as a horticultural crop with one of the highest ascorbic acid contents, are negatively affected by detrimental environmental conditions both in terms of quality and productivity. In peppers, the high level of ascorbic acid is not only a nutrient substance but also plays a role in environmental stress, i.e., drought stress. When suffering from drought stress, plants accumulate dehydrins, which play important roles in the stress response. Here, we isolated an SK3-type DHN gene CaDHN2 from peppers. CaDHN2 was located in the nucleus, cytoplasm, and cell membrane. In CaDHN2-silenced peppers, which are generated by virus-induced gene silencing (VIGS), the survival rate is much lower, the electrolytic leakage is higher, and the accumulation of reactive oxygen species (ROS) is greater when compared with the control under drought stress. Moreover, when CaDHN2 (CaDHN2-OE) is overexpressed in Arabidopsis, theoverexpressing plants show enhanced drought tolerance, increased antioxidant enzyme activities, and lower ROS content. Based on yeast two-hybrid (Y2H), GST-pull down, and bimolecular fluorescence complementation (BiFC) results, we found that CaDHN2 interacts with CaGGP1, the key enzyme in ascorbic acid (AsA) synthesis, in the cytoplasm. Accordingly, the level of ascorbic acid is highly reduced in CaDHN2-silenced peppers, indicating that CaDHN2 interacts with CaGGP1 to affect the synthesis of ascorbic acid under drought stress, thus improving the drought tolerance of peppers. Our research provides a basis for further study of the function of DHN genes.

Plant dehydrins and dehydrin-like proteins: characterization and participation in abiotic stress response

Abiotic stress has a significant impact on plant growth and development. It causes changes in the subcellular organelles, which, due to their stress sensitivity, can be affected. Cellular components involved in the abiotic stress response include dehydrins, widely distributed proteins forming a class II of late embryogenesis abundant protein family with characteristic properties including the presence of evolutionarily conserved sequence motifs (including lysine-rich K-segment, N-terminal Y-segment, and often phosphorylated S motif) and high hydrophilicity and disordered structure in the unbound state. Selected dehydrins and few poorly characterized dehydrin-like proteins participate in cellular stress acclimation and are also shown to interact with organelles. Through their functioning in stabilizing biological membranes and binding reactive oxygen species, dehydrins and dehydrin-like proteins contribute to the protection of fragile organellar structures under adverse conditions. Our review characterizes the participation of plant dehydrins and dehydrin-like proteins (including some organellar proteins) in plant acclimation to diverse abiotic stress conditions and summarizes recent updates on their structure (the identification of dehydrin less conserved motifs), classification (new proposed subclasses), tissue- and developmentally specific accumulation, and key cellular activities (including organellar protection under stress acclimation). Recent findings on the subcellular localization (with emphasis on the mitochondria and plastids) and prospective applications of dehydrins and dehydrin-like proteins in functional studies to alleviate the harmful stress consequences by means of plant genetic engineering and a genome editing strategy are also discussed.

The cationic nature of lysine-rich segments modulates the structural and biochemical properties of wild potato FSK3 dehydrin

Dehydrins are hydrophilic stress-induced proteins that are thought to protect cellular machinery from the adverse effect of dehydration caused by low temperature, drought, or salinity. In the previous study, acidic FSK₃ dehydrin DHN24 from Solanum sogarandinum was found to accumulate at multiple sites in phloem cells in response to cold treatment. This study investigated the biochemical and structural properties of recombinant DHN24. It was shown that the overexpression of DHN24 in Escherichia coli led to the inhibition of bacterial growth. The purified DHN24 was found to protect lactate dehydrogenase from freeze-induced denaturation. Circular dichroism (CD) analysis showed that DHN24 was disordered in aqueous solutions, but adopted α-helical conformation in a membrane-mimetic environment using sodium dodecyl sulfate micelles. DHN24 also interacted with anionic phosphatidic acid (PA). DHN24 contains four lysine-rich regions including three K-segments and a region upstream of the S-segment. The role of their local cationic nature is unknown. These segments are predicted to form helical structures. The CD analysis of mutant proteins in the membrane-mimetic environment matched these predictions most closely, revealing that the positively charged lysine residues in these regions promoted disorder-to-order transitions. Moreover, the inhibition of bacterial growth and interactions with PA were regulated by the local cationic nature of DHN24, while no such regulation was observed for its cryoprotective activity. The importance of the positive charge of the lysine-rich segments and disordered structure for DHN24 activity is discussed in relation to its possible biological function.

Physiological, Structural, and Functional Insights Into the Cryoprotection of Membranes by the Dehydrins

Plants can be exposed to cold temperatures and have therefore evolved several mechanisms to prevent damage caused by freezing. One of the most important targets are membranes, which are particularly susceptible to cold damage. To protect against such abiotic stresses, plants express a family of proteins known as late embryogenesis abundant (LEA) proteins. Many LEA proteins are intrinsically disordered, that is, they do not contain stable secondary or tertiary structures alone in solution. These proteins have been shown in a number of studies to protect plants from damage caused by cold, drought, salinity, and osmotic stress. In this family, the most studied proteins are the type II LEA proteins, better known as dehydrins (dehydration-induced proteins). Many physiological studies have shown that dehydrins are often located near the membrane during abiotic stress and that the expression of dehydrins helps to prevent the formation of oxidation-modified lipids and reduce the amount of electrolyte leakage, two hallmarks of damaged membranes. One of the earliest biophysical clues that dehydrins are involved in membrane cryoprotection came from in vitro studies that demonstrated a binding interaction between the protein and membranes. Subsequent work has shown that one conserved motif, known as K-segments, is involved in binding, while recent studies have used NMR to explore the residue specific structure of dehydrins when bound to membranes. The biophysical techniques also provide insight into the mechanism by which dehydrins protect the membrane from cold stress, which appears to mainly involve the lowering of the transition temperature.