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

Mechanical wounding improves salt tolerance by maintaining root ion homeostasis in a desert shrub

Soil salinization, especially in arid environments, is a leading cause of land degradation and desertification. Excessive salt in the soil is detrimental to plants. Plants have developed various sophisticated regulatory mechanisms that allow them to withstand adverse environments. Through cross-adaptation, plants improve their resistance to an adverse condition after experiencing a different kind of adversity. Our analysis of Ammopiptanthus nanus, a desert shrub, showed that mechanical wounding activates the biosynthesis of jasmonic acid (JA) and abscisic acid (ABA), enhancing plasma membrane H+-ATPase activity to establish an electrochemical gradient that promotes Na+ extrusion via Na+/H+ antiporters. Mechanical wounding reduces K+ loss under salt stress, improving the K/Na and maintaining root ion balance. Meanwhile, mechanical damage enhances the activity of antioxidant enzymes and the content of osmotic substances, working together with cellular ions to alleviate water loss and growth inhibition under salt stress. This study provides new insights and approaches for enhancing salt tolerance and stress adaptation in plants by elucidating the signaling mechanisms of cross-adaptation.

The MsDHN1-MsPIP2;1-MsmMYB module orchestrates the trade-off between growth and survival of alfalfa in response to drought stress

Dehydrins and aquaporins play crucial roles in plant growth and stress responses by acting as protector and controlling water transport across membranes, respectively. MsDHN1 (dehydrin) and MsPIP2;1 (aquaporin) were demonstrated to interact with a membrane-anchored MYB protein, MsmMYB (as mMYB) in plasma membrane under normal condition. MsDHN1, MsPIP2;1 and MsDHN1-MsPIP2;1 positively regulated alfalfa tolerance to water deficiency. Water deficiency caused phosphorylation of MsPIP2;1 at Ser 272, which led to release C terminus of mMYB (mMYBΔ83) from plasma membrane and translocate to nucleus, where C terminus of MsDHN1 interacted with mMYBΔ83, and promoted mMYBΔ83 transcriptional activity in response to water deficiency. Overexpression of mMYB and mMYBΔ83 down-regulated the expression of MsCESA3, but up-regulated MsCESA7 expression by directly binding to their promoters, and resulted in high drought tolerance in transgenic hairy roots. These results indicate that the MsDHN1-MsPIP2;1-MsMYB module serves as a key regulator in alfalfa against drought stress.

The positive impact of the NtTAS14-like1 gene on osmotic stress response in Nicotiana tabacum

KEY MESSAGE

NtTAS14-like1 enhances osmotic tolerance through coordinately activating the expression of osmotic- and ABA-related genes. Osmotic stress is one of the most important limiting factors for tobacco (Nicotiana tabacum) growth and development. Dehydrin proteins are widely involved in plant adaptation to osmotic stress, but few of these proteins have been functionally characterized in tobacco. Here, to identify genes required for osmotic stress response in tobacco, an encoding dehydrin protein gene NtTAS14-like1 was isolated based on RNA sequence data. The expression of NtTAS14-like1 was obviously induced by mannitol and abscisic acid (ABA) treatments. Knock down of NtTAS14-like1 expression reduced osmotic tolerance, while overexpression of NtTAS14-like1 conferred tolerance to osmotic stress in transgenic tobacco plants, as determined by physiological analysis of the relative electrolyte leakage and malonaldehyde accumulation. Further expression analysis by quantitative real-time PCR indicated that NtTAS14-like1 participates in osmotic stress response possibly through coordinately activating osmotic- and ABA-related genes expression, such as late embryogenesis abundant (NtLEA5), early responsive to dehydration 10C (NtERD10C), calcium-dependent protein kinase 2 (NtCDPK2), ABA-responsive element-binding protein (NtAREB), ABA-responsive element-binding factor 1 (NtABF1), dehydration-responsive element-binding genes (NtDREB2A), xanthoxin dehydrogenase/reductase (NtABA2), ABA-aldehyde oxidase 3 (NtAAO3), 9-cis-epoxycarotenoid dioxygenase (NtNCED3). Together, this study will facilitate to improve our understandings of molecular and functional properties of plant TAS14 proteins and to improve genetic evidence on the involvement of the NtTAS14-like1 in osmotic stress response of tobacco.

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.

AnWRKY29 from the desert xerophytic evergreen Ammopiptanthus nanus improves drought tolerance through osmoregulation in transgenic plants

As a significant transcription factor family in plants, WRKYs have a crucial role in responding to different adverse environments. They have been repeatedly demonstrated to contribute to drought resistance. However, no systematic exploration of the WRKY family has been reported in the evergreen shrub Ammopiptanthus nanus under drought conditions. Here, we showed that AnWRKY29 expression is strongly induced under drought stress. AnWRKY29 belongs to the group IIe of WRKY gene family. To characterize the function of AnWRKY29, we generated transgenic plants overexpressing this gene in Arabidopsis thaliana. We determined that AnWRKY29 overexpression of mainly improves the drought resistance of transgenic plants to water stress by reducing water loss, preventing electrolyte leakage, and increasing the absorption of inorganic ions. In addition, the AnWRKY29 transgenic plants synthesized more trehalose under water stress. The overexpression of AnWRKY29 also enhanced the antioxidant and osmoregulation capacity of transgenic plants by increasing the activities of catalase, peroxidase and superoxide dismutase, thus increasing the scavenging of reactive oxygen species and propylene glycol synthesis aldehyde oxidase. In summary, our study shows that AnWRKY29 plays an important role in the drought tolerance pathway in plants.

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.

Genetic Diversity and Population Differentiation of a Chinese Endangered Plant Ammopiptanthus nanus (M. Pop.) Cheng f

Ammopiptanthus nanus (M. Pop.) Cheng f. is a very important resource plant that integrates soil and water conservation, afforestation of barren mountains, and ornamental, medicinal, and scientific research functions and is also a critically endangered plant in China, remaining in only six small fragmented populations in the wild. These populations have been suffering from severe anthropomorphic disturbances, causing further losses in genetic diversity. However, its genetic diversity level and genetic differentiation degree among the fragmented populations are still unclear. Inthis study, DNA was extracted from fresh leaves from the remnant populations of A. nanus, and the inter-simple-sequence repeat (ISSR) molecular marker system was used to assess its level of genetic diversity and differentiation. The result was that its genetic diversity is low at both species and population levels, with only 51.70% and 26.84% polymorphic loci, respectively. The Akeqi population had the highest genetic diversity, whereas the Ohsalur and Xiaoerbulak populations had the lowest. There was significant genetic differentiation among the populations, and the value of the genetic differentiation coefficient (Gst) was as high as 0.73, while the gene flow value was as low as 0.19 owing to spatial fragmentation and a serious genetic exchange barrier among the populations. It is suggested that a nature reserve and germplasm banks should be established as soon as possible for elimination of the anthropomorphic disturbances, and mutual introductions between the populations and introduced patches of the species, such as with habitat corridors or stepping stones, should be performed simultaneously to improve the genetic diversity of the isolated populations for the conservation of this plant.

Gene Profiling of the Ascorbate Oxidase Family Genes under Osmotic and Cold Stress Reveals the Role of AnAO5 in Cold Adaptation in Ammopiptanthus nanus

The uplift of the Qinghai Tibet Plateau has led to a drastic change in the climate in Central Asia, from warm and rainy, to dry and less rainfall. Ammopiptanthus nanus, a rare evergreen broad-leaved shrub distributed in the temperate desert region of Central Asia, has survived the drastic climate change in Central Asia caused by the uplift of the Qinghai-Tibet Plateau. Ascorbate oxidase (AO) regulates the redox status of the apoplast by catalyzing the oxidation of ascorbate acid to dehydroascorbic acid, and plays a key role in the adaptation of plants to environmental changes. Analyzing the evolution, environmental response, and biological functions of the AO family of A. nanus is helpful for understanding how plant genome evolution responds to climate change in Central Asia. A total of 16 AOs were identified in A. nanus, all of which contained the ascorbate oxidase domain, most of which contained transmembrane domain, and many were predicted to be localized in the apoplast. Segmental duplication and tandem duplication are the main factors driving the gene amplification of the AO gene family in A. nanus. Gene expression analysis based on transcriptome data and fluorescence quantitative PCR, as well as enzyme activity measurements, showed that the expression levels of AO genes and total enzyme activity decreased under short-term osmotic stress and low-temperature stress, but the expression of some AO genes (AnAO5, AnAO13, and AnAO16) and total enzyme activity increased under 7 days of cold stress. AnAO5 and AnAO11 are targeted by miR4415. Further functional studies on AnAO5 showed that AnAO5 protein was localized in the apoplast. The expression of AnAO5 in yeast cells and the transient expression in tobacco enhanced the tolerance of yeast and tobacco to low-temperature stress, and the overexpression of AnAO5 enhanced the tolerance of Arabidopsis seedlings to cold stress. Our research provides important data for understanding the role of AOs in plant adaptation to environmental change.

Seed Priming with Chitosan Improves Germination Characteristics Associated with Alterations in Antioxidant Defense and Dehydration-Responsive Pathway in White Clover under Water Stress

Water stress decreases seed-germination characteristics and also hinders subsequent seedling establishment. Seed priming with bioactive compounds has been proven as an effective way to improve seed germination under normal and stressful conditions. However, effect and mechanism of seed priming with chitosan (CTS) on improving seed germination and seedling establishment were not well-understood under water-deficit conditions. White clover (Trifolium repens) seeds were pretreated with or without 5 mg/L CTS before being subjected to water stress induced by 18% (w/v) polyethylene glycol 6000 for 7 days of germination in a controlled growth chamber. Results showed that water stress significantly decreased germination percentage, germination vigor, germination index, seed vigor index, and seedling dry weight and also increased mean germination time and accumulation of reactive oxygen species, leading to membrane lipid peroxidation during seed germination. These symptoms could be significantly alleviated by the CTS priming through activating superoxide dismutase, catalase, and peroxidase activities. In addition, seeds pretreated with CTS exhibited significantly higher expression levels of genes encoding dehydration-responsive transcription factors (DREB2, DREB4, and DREB5) and dehydrins (Y2K, Y2SK, and SK2) than those seeds without the CTS priming. Current findings indicated that the CTS-induced tolerance to water stress could be associated with the enhancement in dehydration-responsive pathway during seed germination.