The garlic NF-YC gene, <Emphasis Type="Italic">AsNF-YC8</Emphasis>, positively regulates non-ionic hyperosmotic stress tolerance in tobacco

To investigate the relationship between nuclear factor Y (NF-Y) and stress tolerance in garlic, we cloned a NF-Y family gene AsNF-YC8 from garlic, which was largely upregulated at dehydrate stage. Expression pattern analyses in garlic revealed that AsNF-YC8 is induced through abscisic acid (ABA) and abiotic stresses, such as NaCl and PEG. Compared with wild-type plants, the overexpressing-AsNF-YC8 transgenic tobacco plants showed higher seed germination rates, longer root length and better plant growth under salt and drought stresses. Under drought stress, the transgenic plants maintained higher relative water content (RWC), net photosynthesis, lower levels of malondialdehyde (MDA), and less ion leakage (IL) than wild-type control plants. These results indicate the high tolerance of the transgenic plants to drought stress compared to the WT. The transgenic tobacco lines accumulated less reactive oxygen species (ROS) and exhibited higher antioxidative enzyme activities compared with wild-type (WT) plants under drought stress, which suggested that the overexpression of AsNF-YC8 improves the antioxidant defense system by regulating the activities of these antioxidant enzymes, which in turn protect transgenic lines against drought stress. These results suggest that AsNF-YC8 plays an important role in tolerance to drought and salt stresses.     

A new <Emphasis Type="Italic">Em</Emphasis>-like protein from <Emphasis Type="Italic">Lactuca sativa</Emphasis>, <Emphasis Type="Italic">LsEm1</Emphasis>, enhances drought and salt stress tolerance in <Emphasis Type="Italic">Escherichia coli</Emphasis> and rice

Late embryogenesis abundant (LEA) proteins are closely related to abiotic stress tolerance of plants. In the present study, we identified a novel Em-like gene from lettuce, termed LsEm1, which could be classified into group 1 LEA proteins, and shared high homology with Cynara cardunculus Em protein. The LsEm1 protein contained three different 20-mer conserved elements (C-element, N-element, and M-element) in the C-termini, N-termini, and middle-region, respectively. The LsEm1 mRNAs were accumulated in all examined tissues during the flowering and mature stages, with a little accumulation in the roots and leaves during the seedling stage. Furthermore, the LsEm1 gene was also expressed in response to salt, dehydration, abscisic acid (ABA), and cold stresses in young seedlings. The LsEm1 protein could effectively reduce damage to the lactate dehydrogenase (LDH) and protect LDH activity under desiccation and salt treatments. The Escherichia coli cells overexpressing the LsEm1 gene showed a growth advantage over the control under drought and salt stresses. Moreover, LsEm1-overexpressing rice seeds were relatively sensitive to exogenously applied ABA, suggesting that the LsEm1 gene might depend on an ABA signaling pathway in response to environmental stresses. The transgenic rice plants overexpressing the LsEm1 gene showed higher tolerance to drought and salt stresses than did wild-type (WT) plants on the basis of the germination performances, higher survival rates, higher chlorophyll content, more accumulation of soluble sugar, lower relative electrolyte leakage, and higher superoxide dismutase activity under stress conditions. The LsEm1-overexpressing rice lines also showed less yield loss compared with WT rice under stress conditions. Furthermore, the LsEm1 gene had a positive effect on the expression of the OsCDPK9, OsCDPK13, OsCDPK15, OsCDPK25, and rab21 (rab16a) genes in transgenic rice under drought and salt stress conditions, implying that overexpression of these genes may be involved in the enhanced drought and salt tolerance of transgenic rice. Thus, this work paves the way for improvement in tolerance of crops by genetic engineering breeding.     

A Leucine-Rich Repeat Receptor-like Kinase from the Antarctic Moss <Emphasis Type="Italic">Pohlia nutans</Emphasis> Confers Salinity and ABA Stress Tolerance

Plant leucine-rich repeats receptor-like kinases (LRR-RLKs) play key roles in plant growth, development, and responses to environmental stresses. However, the functions of LRR-RLKs in bryophytes are still not well documented. Here, a putative LRR-RLK gene, PnLRR-RLK, was cloned and characterized from the Antarctic moss Pohlia nutans. Phylogenetic analysis revealed that PnLRR-RLK protein was clustered with the Arabidopsis thaliana LRR XI family proteins. Subcellular localization analysis of PnLRR-RLK revealed that it was mainly localized on plasma membrane. The expression of PnLRR-RLK was induced by mock high salinity, cold, drought, and exogenously supplied abscisic acid (ABA) and methyl jasmonate (MeJA). Meanwhile, the overexpression of PnLRR-RLK showed an increased tolerance of transgenic Arabidopsis to salt and ABA stresses than that of the wild type (WT) plants. Furthermore, the expression levels of several salt tolerance genes (AtHKT1, AtSOS3, AtP5CS1, and AtADH1) and an ABA negatively regulating gene AtABI1 were significantly increased in transgenic plants. Meanwhile, the expression levels of ABA biosynthesis genes (AtNCED3, AtABA1, and AtAAO3) and ABA early response genes (AtMYB2, AtRD22, AtRD29A, and AtDREB2A) were decreased in transgenic Arabidopsis after salt stress treatment. Therefore, these results suggested that PnLRR-RLK might involve in regulating salt stress-related and ABA-dependent signaling pathway, thereby contribute to the salinity tolerance of the Antarctic moss P. nutans.     

Over-Expression of <Emphasis Type="Italic">PmHSP17.9</Emphasis> in Transgenic <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> Confers Thermotolerance

Small heat shock proteins (sHSPs) have been shown to be involved in stress tolerance. However, their functions in Prunus mume under heat treatment are poorly characterized. To improve our understanding of sHSPs, we cloned a sHSP gene, PmHSP17.9, from P. mume. Sequence alignment and phylogenetic analysis indicated that PmHSP17.9 was a member of plant cytosolic class III sHSPs. Besides heat stress, PmHSP17.9 was also upregulated by salt, dehydration, oxidative stresses and ABA treatment. Leaves of transgenic Arabidopsis thaliana that ectopically express PmHSP17.9 accumulated less O₂ ^? and H₂O₂ compared with wild type (WT) after 42 °C treatment for 6 h. Over-expression of PmHSP17.9 in transgenic Arabidopsis enhanced seedling thermotolerance by decreased relative electrolyte leakage and MDA content under heat stress treatment when compared to WT plants. In addition, the induced expression of HSP101, HSFA2, and delta 1-pyrroline-5-carboxylate synthase (P5CS) under heat stress was more pronounced in transgenic plants than in WT plants. These results support the positive role of PmHSP17.9 in response to heat stress treatment.     

Overexpression of soybean <Emphasis Type="Italic">GmERF9</Emphasis> enhances the tolerance to drought and cold in the transgenic tobacco

Ethylene response factors (ERFs) are widespread in plants, which are widely involved in plant response to biotic and abiotic stress. In this research, a soybean gene, GmERF9, was identified and the function was characterized. The results showed that GmERF9 contained a typical AP2/ERF binding domain and a putative nuclear localization signal sequence. The real-time fluorescence quantitative PCR (qPCR) revealed that the expression of GmERF9 could be induced by ethylene (ET), abscisic acid (ABA), drought, salt and cold stresses. GmERF9 protein could specifically bind to the GCC-box and activate the expression of the reporter gene in the yeast cells and tobacco leaves. Overexpression of GmERF9 enhanced the expression of pathogenesis-related (PR) genes, including PR1, PR2, Osmotin (PR5), and SAR8.2. Also, the overexpression of GmERF9 increased the accumulation of proline and soluble carbohydrate, and decreased the accumulation of malondialdehyde under drought and cold stresses in the transgenic tobacco compared to the wild type (WT) tobacco, which indicated that GmERF9 enhanced the tolerance to drought and cold stresses in the transgenic tobacco. In summary, the function of GmERF9 is involved in the response to environmental stresses for plants, which can be used as a candidate gene for genetic engineering of crops.     

An aquaporin gene from halophyte <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis>, <Emphasis Type="Italic">SpAQP1</Emphasis>, increases salt tolerance in transgenic tobacco

Key message

SpAQP1 was strongly induced by salt in an ABA-independent way, promoted seed germination and root growth in transgenic tobaccos and increased salt tolerance by increasing the activities of antioxidative enzymes.

Abstract

Aquaporin (AQP) plays crucial roles in the responses of plant to abiotic stresses such as drought, salt and cold. Compared to glycophytes, halophytes often have excellent salt and drought tolerances. To uncover the molecular mechanism of halophyte Sesuvium portulacastrum tolerance to salt, in this study, an AQP gene, SpAQP1, from S. portulacastrum was isolated and characterized. The amino acid sequence of SpAQP1 shared high homology with that of plant plasma membrane intrinsic proteins (PIPs) and contained the distinct molecular features of PIPs. In the phylogenic tree, SpAQP1 was evidently classified as the PIP2 subfamily. SpAQP1 is expressed in roots, stems and leaves, and was significantly induced by NaCl treatment and inhibited by abscisic acid (ABA) treatment. When heterologously expressed in yeast and tobacco, SpAQP1 enhanced the salt tolerance of yeast strains and tobacco plants and promoted seed germination and root growth under salt stress in transgenic plants. The activity of antioxidative enzymes including superoxide dismutase, peroxidase and catalase was increased in transgenic plants overexpressing SpAQP1. Taken together, our studies suggested that SpAQP1 functioned in the responses of S. portulacastrum to salt stress and could increase salt tolerance by enhancing the antioxidative activity of plants.

     

Overexpression of <Emphasis Type="Italic">ThGSTZ1</Emphasis> from <Emphasis Type="Italic">Tamarix hispida</Emphasis> improves tolerance to exogenous ABA and methyl viologen

Key message

Molecular analysis of a zeta subfamily GST gene from T. hispida involved in ABA and methyl viologen tolerance in transgenic Arabidopsis and Tamarix.

Abstract

Glutathione S-transferase (GST) genes are important for the improvement of plant abiotic stress tolerance, and our previous study demonstrated that the ThGSTZ1 gene from Tamarix hispida improves plant salt and drought tolerance. To further understand the role of ThGSTZ1 in the response of plants to abscisic acid (ABA) and oxidative stress, three ThGSTZ1-overexpressing transgenic Arabidopsis thaliana lines were analyzed in the current study. The results showed that the transgenic lines exhibited higher biomass accumulation, higher activities of GST and other protective enzymes, and less reactive oxygen species (ROS) and cell damage than wild-type (WT) plants under ABA and methyl viologen (MV) stress. In addition, the analysis of a transgenic T. hispida line transiently expressing ThGSTZ1 confirmed these results. The activities of GST, glutathione peroxidase, and superoxide dismutase were markedly higher in the ThGSTZ1-overexpressing lines compared with the control lines under both ABA and MV treatments, and the transgenic lines also exhibited a lower degree of electrolyte leakage (EL) and a decreased H₂O₂ content. All these results suggested that ThGSTZ1 can also improve plant ABA and oxidation tolerance by regulating ROS metabolism and that ThGSTZ1 represents an excellent candidate gene for molecular breeding to increase plant stress tolerance.

     

The <Emphasis Type="Italic">SlCMO</Emphasis> Gene Driven by Its Own Promoter Enhances Salt Tolerance of Transgenic Tomato Without Affecting Growth and Yield

Choline monooxygenase (CMO) is a key enzyme involved in betaine synthesis and our preliminary work has shown that the SlCMO gene promoter (pC5: ??267 to +?128 base pair), cloned from Suaeda liaotungensis, is salt-inducible. In the present study, pC5-SlCMO was transferred into tomato (Solanum lycopersicon L. ‘Micro-Tom’) plants via Agrobacterium mediation. Homozygous transgenic plants were selected using quantitative real-time polymerase chain reaction. The expression of SlCMO in pC5-SlCMO transgenic plants was induced by salinity. Under salt tolerance, betaine content, chlorophyll content, and net photosynthetic rate were higher in transgenic plants than in wild-type (WT) plants. Proline content was lower in transgenic plants than in WT plants. Under normal conditions, seed germination, length of the whole plant, dry weight, and fruit products of transgenic plants were the same as in WT plants. These results demonstrated that the pC5 promoter can drive increased expression of SlCMO in transgenic tomato plants under salt stress and increase salt tolerance without affecting plant growth and yield.     

SlAGO4A,a core factor of RNA-directed DNA methylation (RdDM) pathway,plays an important role under salt and drought stress in tomato

In Arabidopsis, it has been clarified that AGO4 protein is implicated in a phenomenon termed RNA-directed DNA methylation (RdDM). Previously, four orthologs of AtAGO4 were cloned in tomato, designated as SlAGO4A–SlAGO4D. Here, we studied the role of the SlAGO4A gene in regulating salt and drought tolerance in tomato. SlAGO4A-down-regulating (AS) transgenic tomato plants showed enhanced tolerance to salt and drought stress compared to wild-type (WT) and SlAGO4A-overexpressing (OE) transgenic plants, as assessed by physiological parameters such as seed germination rate, primary root length, chlorophyll/proline/MDA/soluble sugar/RWC content, and survival rate. Moreover, several genes involved in ROS scavenging and plant defense, including CAT, SOD, GST, POD, APX, LOX, and PR1, were up- or down-regulated consistently under salt and drought stress. Notably, expression levels of some DNA methyltransferase genes and RNAi pathway genes were significantly lower in AS plants than in WT. Taken together, our results suggest that SlAGO4A gene plays a negative role under salt and drought stress in tomato probably through the modulation of DNA methylation as well as the classical RNAi pathway. Hence, it may serve as a useful biotechnological tool for the genetic improvement of stress tolerance in crops.