Heterologous expression of antifreeze protein gene AnAFP from Ammopiptanthus nanus enhances cold tolerance in Escherichia coli and tobacco

AnWRKY29 and AnHSP90 synergistically modulate trehalose levels in a desert shrub leaves during osmotic stress

Trehalose, a biological macromolecule with osmotic adjustment properties, plays a crucial role during osmotic stress. As a psammophyte, Ammopiptanthus nanus relies on the accumulation of organic solutes to respond to osmotic stress. We utilized virus-induced gene silencing technology for the first time in the desert shrub A. nanus to confirm the central regulatory role of AnWRKY29 in osmotic stress, as it controls the transcription of AnTPS11 (trehalose-6-phosphate synthase 11). Further investigation has shown that AnHSP90 may interact with AnWRKY29. The AnHSP90 gene is sensitive to osmotic stress, underscoring its pivotal role in orchestrating the response to such adverse conditions. By directly targeting the W-box element within the AnTPS11 promoter, AnWRKY29 effectively enhances the transcriptional activity of AnTPS11, which is facilitated by AnHSP90. This discovery highlights the critical role of AnWRKY29 and AnHSP90 in enabling organisms to adapt to and cope effectively with osmotic stress, which can be a crucial factor in A. nanus survival and overall ecological resilience. Collectively, uncovering the molecular mechanisms underlying the osmotic responses of A. nanus is paramount for comprehending and augmenting the osmotic tolerance mechanisms of psammophyte shrub plants.

Identification and characterization of AnICE1 and AnCBFs involved in cold tolerance from Ammopiptanthus nanus

The ICE-CBF-COR pathway plays a vital role in improving the cold tolerance of plants. As an evergreen small shrub, Ammopiptanthus nanus has a high tolerance to cold stress because of its special growth conditions. Regrettably, no cold-responsive genes in the ICE-CBF-COR pathway have been reported in A. nanus. In the current study, we isolated AnICE1, AnCBF1, and AnCBF2 in A. nanus and analyzed their sequence structure. Evolutionary analysis indicated that these genes are most closely related to those from Ammopiptanthus mongolicus, Glycine max, Spatholobus suberectus, and Cajanus cajan, all belonging to the Fabaceae. Expression analysis showed that the expression levels of these genes were induced under cold stress and treatment with several plant hormones. As a critical upstream regulator in the ICE-CBF-COR pathway, the function of AnICE1 was further identified. The subcellular localization indicated that AnICE1 is predominantly localized in the plasma membrane and less in the nucleus. Overexpression of AnICE1 in Arabidopsis thaliana improved seed germination and growth of transgenic seedlings during cold stress. Moreover, some physiological indices such as relative electrical conductivity, contents of proline and malondialdehyde, catalase activity, and Nitro Blue tetrazolium and 3.3'-diaminobenzidine staining were investigated by transient expression in A. nanus seedlings and stable overexpression in A. thaliana. These results indicated that AnICE1 enhanced cold tolerance in A. nanus and transgenic A. thaliana. This study is significant for understanding the cold-resistant mechanism of ICE and CBF genes in A. nanus.

Antifreeze protein from Ammopiptanthus nanus functions in temperature-stress through domain A

Temperature stress restricts plant growth and development. Antifreeze protein (AFP) can improve plants antifreeze ability. In our previous study, the AnAFP gene cloned from Ammopiptanthus nanus was confirmed to be an excellent candidate enhancing plant cold resistance. But, AnAFP protein shared similar structures with KnS type dehydrins including K, N and S domains except ice crystal binding domain A. Here, we generated AnAFPΔA, AnAFPΔK, AnAFPΔN and AnAFPΔS, and transformed them into ordinary and cold sensitive strains of E. coli, and Arabidopsis KS type dehydrin mutant to evaluate their function. Expression of AnAFPΔA decreases cold and heat tolerance in E. coli, meanwhile, AnAFP enhances heat tolerance in Arabidopsis, suggesting that domain A is a thermal stable functional domain. AnAFP, AnAFPΔA and AnAFPΔS localize in whole cell, but AnAFPΔK and AnAFPΔN only localizes in nucleus and cytoplasm, respectively, exhibiting that K and N domains control localization of AnAFP. Likewise, K domain blocks interaction between AnAFP and AnICE1. The result of RT-qPCR showed that expression of AnAFP, AnICE1 and AnCBF genes was significantly induced by high-temperature, indicating that the AnAFP is likely regulated by ICE1-CBF-COR signal pathway. Taken together, the study provides insights into understanding the mechanism of AnAFP in response to temperature stress and gene resource to improve heat or cold tolerance of plants in transgenic engineering.

Herbivore exposure alters ion fluxes and improves salt tolerance in a desert shrub

Plants have evolved complex mechanisms that allow them to withstand multiple environmental stresses, including biotic and abiotic stresses. Here, we investigated the interaction between herbivore exposure and salt stress of Ammopiptanthus nanus, a desert shrub. We found that jasmonic acid (JA) was involved in plant responses to both herbivore attack and salt stress, leading to an increased NaCl stress tolerance for herbivore-pretreated plants and increase in K⁺ /Na⁺ ratio in roots. Further evidence revealed the mechanism by which herbivore improved plant NaCl tolerance. Herbivore pretreatment reduced K⁺ efflux and increased Na⁺ efflux in plants subjected to long-term, short-term, or transient NaCl stress. Moreover, herbivore pretreatment promoted H⁺ efflux by increasing plasma membrane H⁺ -adenosine triphosphate (ATP)ase activity. This H⁺ efflux creates a transmembrane proton motive force that drives the Na⁺ /H⁺ antiporter to expel excess Na⁺ into the external medium. In addition, high cytosolic Ca²⁺ was observed in the roots of herbivore-treated plants exposed to NaCl, and this effect may be regulated by H⁺ -ATPase. Taken together, herbivore exposure enhances A. nanus tolerance to salt stress by activating the JA-signalling pathway, increasing plasma membrane H⁺ -ATPase activity, promoting cytosolic Ca²⁺ accumulation, and then restricting K⁺ leakage and reducing Na⁺ accumulation in the cytosol.

A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering

Antifreeze proteins (AFPs) confer the ability to survive at subzero temperatures and are found in many different organisms, including fish, plants, and insects. They prevent the formation of ice crystals by non-colligative adsorption to the ice surface and are essential for the survival of organisms in cold environments. These proteins are also widely used for cryopreservation, food technology, and metabolic genetic engineering over a range of sources and recipient cell types. This review summarizes successful applications of AFPs in the cryopreservation of animals, insects, and plants, and discusses challenges encountered in cryopreservation. Applications in metabolic genetic engineering are also described, specifically with the overexpression of AFP genes derived from different organisms to provide freeze protection to sensitive crops seasonally exposed to subzero temperatures. This review will provide information about potential applications of AFPs in the cryopreservation of animals and plants as well as in plant metabolic genetic engineering in hopes of furthering the development of cold-tolerant organisms.

Drought and heat stress-related proteins: an update about their functional relevance in imparting stress tolerance in agricultural crops

We describe here the recent developments about the involvement of diverse stress-related proteins in sensing, signaling, and defending the cells in plants in response to drought or/and heat stress. In the current era of global climate drift, plant growth and productivity are often limited by various environmental stresses, especially drought and heat. Adaptation to abiotic stress is a multigenic process involving maintenance of homeostasis for proper survival under adverse environment. It has been widely observed that a series of proteins respond to heat and drought conditions at both transcriptional and translational levels. The proteins are involved in various signaling events, act as key transcriptional activators and saviors of plants under extreme environments. A detailed insight about the functional aspects of diverse stress-responsive proteins may assist in unraveling various stress resilience mechanisms in plants. Furthermore, by identifying the metabolic proteins associated with drought and heat tolerance, tolerant varieties can be produced through transgenic/recombinant technologies. A large number of regulatory and functional stress-associated proteins are reported to participate in response to heat and drought stresses, such as protein kinases, phosphatases, transcription factors, and late embryogenesis abundant proteins, dehydrins, osmotins, and heat shock proteins, which may be similar or unique to stress treatments. Few studies have revealed that cellular response to combined drought and heat stresses is distinctive, compared to their individual treatments. In this review, we would mainly focus on the new developments about various stress sensors and receptors, transcription factors, chaperones, and stress-associated proteins involved in drought or/and heat stresses, and their possible role in augmenting stress tolerance in crops.

A novel class I Chitinase from Hippophae rhamnoides: Indications for participating in ICE-CBF cold stress signaling pathway

Plant chitinases are the members of PR (Pathogenesis related) proteins family and protect plants from biotic and abiotic stress. A novel chitinase HrCHI1 (Accession number JQ289153) of 954bp ORF encoding 317 amino acids protein was cloned, expressed and characterized from seabuckthorn, a cold/freeze tolerant shrub. The 3D structure (predicted with I-TASSER server) showed highest homology with Oryza sativa class I chitinase (PDB 2dkvA). Putative promoter region (obtained by genome walking) showed GCC box, E-boxes, the binding site for bHLH proteins and DRE elements, the CBF (C-repeat binding factor) binding site besides TATA and CAAT boxes. The gel shift assay with the nuclear extract indicated that the HrCHI1 might be participating in CBF/ERF dependent cold stress signaling pathway. The quantitative transcript profiling supported this observation as cold induced expression of HrCBF peaked earlier (at 1h) while HrCHI1 peaked latter (after 3h) indicating HrCHI1 expression might be induced by HrCBF. Further, HrCHI1 expression was methyl jasmonate (MeJa) dependent and salicylic acid (SA) independent. HrCHI1 was expressed in E. coli and purified using chitin affinity chromatography. It showed 512U/mg chitinase hydrolytic activity and resolved as a 34kDa spot with a slightly basic pI (8.5) on a 2-D gel. The E. coli cells containing recombinant chitinase showed higher rate of growth in cold in comparison with the cells containing the empty vector. In conclusion, we have isolated and characterized a cold responsive basic class I chitinase which is regulated by MeJa and seems to be functioning via CBF/ERF dependent cold stress signaling pathway.

Overexpression of a phospholipase Dα gene from Ammopiptanthus nanus enhances salt tolerance of phospholipase Dα1-deficient Arabidopsis mutant

A phospholipase Dα gene ( AnPLDα ) was cloned from xerophytic desert plant Ammopiptanthus nanus and its overexpression enhanced salt tolerance of a PLDα1 deficient Arabidopsis mutant. Phospholipase Dα (PLDα) hydrolyzes phosphatidylcholine to produce phosphatidic acid, and plays crucial role in plant tolerance to abiotic stress. In this study, a phospholipase Dα gene (AnPLDα) was cloned from xerophyte Ammopiptanthus nanus by the methods of homologous cloning and rapid amplification of cDNA ends, and evaluated for its function in stress tolerance. The full-length cDNA was 2832 bp long, containing an open reading frame of 2427 bp that encodes 808 amino acids. The putative protein was predicted to be localized to the cytoplasm and this was confirmed by transient expression of a fluorescent fusion protein. The endogenous expression of the AnPLDα gene was induced by high salt, dehydration, cold and abscisic acid. The heterologous expression of the AnPLDα gene improved salt tolerance of an Arabidopsis pldα1 knocked out mutant, and positively regulated the expression of the AtABI, AtNCED, AtRD29A, AtRD29B and AtADH genes. Therefore, the AnPLDα gene was concluded to be involved in response to abiotic stress. The AnPLDα gene is a hopeful candidate for transgenic application to improve stress tolerance of commercial crops.

Cloning and functional validation of molybdenum cofactor sulfurase gene from Ammopiptanthus nanus

The molybdenum cofactor sulfurase gene ( AnMCSU ) was cloned from xerophytic desert plant Ammopiptanthus nanus and validated for its function of tolerance toward abiotic stresses by heterologous expression in Arabidopsis thaliana. Molybdenum cofactor sulfurase participates in catalyzing biosynthesis of abscisic acid, which plays a crucial role in the response of plants to abiotic stresses. In this study, we cloned molybdenum cofactor sulfurase gene (AnMCSU) from a super-xerophytic desert plant, Ammopiptanthus nanus, by using rapid amplification of cDNA ends method. This gene has a total length of 2544 bp, with a 5'- and a 3'-untranslated region of 167 and 88 bp, and an open reading frame of 2289 bp, which encodes an 84.85 kDa protein of 762 amino acids. The putative amino acid sequence shares high homology and conserved amino acid residues crucial for the function of molybdenum cofactor sulfurases with other leguminous species. The encoded protein of the AnMCSU gene was located in the cytoplasm by transient expression in Nicotiana benthamiana. The result of real-time quantitative PCR showed that the expression of the AnMCSU gene was induced by heat, dehydration, high salt stresses, and ABA induction, and inhibited by cold stress. The heterologous expression of the AnMCSU gene significantly enhanced the tolerance of Arabidopsis thaliana to high salt, cold, osmotic stresses, and abscisic acid induction. All these results suggest that the AnMCSU gene might play a crucial role in the adaptation of A. nanus to abiotic stress and has potential to be applied to transgenic improvement of commercial crops.

Heterologous expression of betaine aldehyde dehydrogenase gene from Ammopiptanthus nanus confers high salt and heat tolerance to Escherichia coli

Betaine aldehyde dehydrogenase (BADH) catalyzes the synthesis of glycine betaine, a regulator of osmosis, and therefore BADH is considered to play a significant role in response of plants to abiotic stresses. Here, based on the conserved residues of the deduced amino acid sequences of the homologous BADH genes, we cloned the AnBADH gene from the xerophytic leguminous plant Ammopiptanthus nanus by using reverse transcription PCR and rapid amplification of cDNA ends. The full-length cDNA is 1,868 bp long without intron, and contains an open reading frame of 1512 bp, and 3'- and 5'-untranslated regions of 294 and 62 bp. It encodes a 54.71 kDa protein of 503 amino acids. The deduced amino acid sequence shares high homology, conserved amino acid residues and sequence motifs crucial for the function with the BADHs in other leguminous species. The sequence of the open reading frame was used to construct a prokaryotic expression vector pET32a-AnBADH, and transform Escherichia coli. The transformants expressed the heterologous AnBADH gene under the induction of isopropyl β-D-thiogalactopyranoside, and demonstrated significant enhancement of salt and heat tolerance under the stress conditions of 700 mmol L(-1) NaCl and 55°C high temperature. This result suggests that the AnBADH gene might play a crucial role in adaption of A. nanus to the abiotic stresses, and have the potential to be applied to transgenic operations of commercially important crops for improvement of abiotic tolerance.