Overexpression of <Emphasis Type="Italic">MuHSP70</Emphasis> gene from <Emphasis Type="Italic">Macrotyloma uniflorum</Emphasis> confers multiple abiotic stress tolerance in transgenic <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

A 70-KD heat shock protein (HSP70) is one of the most conserved chaperones. It is involved in de novo protein folding and prevents the aggregation of unfolded proteins under lethal environmental factors. The purpose of this study is to characterise a MuHSP70 from horsegram (Macrotyloma uniflorum) and elucidating its role in stress tolerance of plants. A MuHSP70 was cloned and characterised from a natural drought stress tolerant HPK4 variety of horsegram (M. uniflorum). For functional characterization, MuHSP70 was overexpressed in transgenic Arabidopsis. Overexpression of MuHSP70 was found to provide tolerance to the transgenic Arabidopsis against various stresses such as heat, cold, drought, salinity and oxidative stress. MuHSP70 transgenics were observed to maintain the shoot biomass, root length, relative water content, and chlorophyll content during exposure to multi-stresses relative to non-transgenic control. Transgenic lines have further shown the reduced levels of MDA, H₂O₂, and proteolytic activity. Together, these findings suggest that overexpression of MuHSP70 plays an important role in improving abiotic stress tolerance and could be a crucial candidate gene for exploration in crop improvement program.     

Overexpression of a peroxiredoxin gene from <Emphasis Type="Italic">Tamarix hispida</Emphasis>, <Emphasis Type="Italic">ThPrx1</Emphasis>, confers tolerance to oxidative stress in yeast and Arabidopsis

Peroxiredoxins (Prxs) are ubiquitous thiol-specific antioxidant enzymes that are critically involved in cell defense and protect cells from oxidative damage. In this study, a putative Type II Prx (ThPrx1) was identified and characterized from Tamarix hispida. The expression of ThPrx1 is highly induced in response to hydrogen peroxide (H₂O₂) and methyl viologen (MV) stresses. When expressed ectopically, ThPrx1 showed enhanced tolerance against oxidative stress in yeast and Arabidopsis. In addition, transgenic Arabidopsis plants overexpressing ThPrx1 displayed improved seedling survival rates and increased root growth and fresh weight gain under H₂O₂ and MV treatments. Moreover, transgenic Arabidopsis plants showed decreased accumulation of H₂O₂, superoxide (O₂^??) and malondialdehyde (MDA), increased superoxide dismutase (SOD) activity compared to wild-type (WT) plants under oxidative stress. Moreover, transgenic plants maintained higher photosynthesis efficiency and lower electrolyte leakage rates than that of WT plants under stress conditions. These results clearly indicated that ThPrx1 plays an important role in cellular redox homeostasis under stress conditions, leading to the maintenance of membrane integrity and increased tolerance to oxidative stress.     

Overexpression of plastidic maize NADP-malate dehydrogenase (<Emphasis Type="Italic">ZmNADP-MDH</Emphasis>) in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> confers tolerance to salt stress

The plastidic C4 Zea mays NADP-malate dehydrogenase (ZmNADP-MDH), responsible for catalysis of oxaloacetate to malate, was overexpressed in Arabidopsis thaliana to assess its impact on photosynthesis and tolerance to salinity stress. Different transgenic lines were produced having ~3–6-fold higher MDH protein abundance and NADP-MDH enzyme activity than vector control. The overexpressors had similar chlorophyll, carotenoid, and protein content as that of vector control. Their photosynthetic electron transport rates, carbon assimilation rate, and consequently fresh weight and dry weight were almost similar. However, these overexpressors were tolerant to salt stress (150 mM NaCl). In saline environment, the Fv/Fm ratio, yield of photosystem II, chlorophyll, and protein content were higher in ZmNADP-MDH overexpressor than vector control. Under identical conditions, the generation of reactive oxygen species (H₂O₂) and production of malondialdehyde, a membrane lipid peroxidation product, were lower in overexpressors. In stress environment, the structural distortion of granal organization and swelling of thylakoids were less pronounced in ZmNADP-MDH overexpressing plants as compared to the vector control. Chloroplastic NADP-MDH in consort with cytosolic and mitochondrial NAD-MDH plays an important role in exporting reducing power (NADPH) and exchange of metabolites between different cellular compartments that maintain the redox homeostasis of the cell via malate valve present in chloroplast envelope membrane. The tolerance of NADP-MDH overexpressors to salt stress could be due to operation of an efficient malate valve that plays a major role in maintaining the cellular redox environment.     

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 <Emphasis Type="Italic">Vitis vinifera</Emphasis> xanthine dehydrogenase gene, <Emphasis Type="Italic">VvXDH</Emphasis>, enhances salinity tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

Xanthine dehydrogenase (EC1.1.1.204; XDH) plays an important role in purine catabolism that catalyzes the oxidative hydroxylation of hypoxanthine to xanthine and of xanthine to uric acid. Long attributed to its role in recycling and remobilization of nitrogen, recently, XDH is implicated in plant stress responses and acclimation, such research efforts, however, have thus far been restricted to Arabidopsis XDH-knockdown/knockout studies. This study, using an ectopic overexpression approach, is expected to provide novel findings. In this study, a XDH gene from Vitis vinifera, named VvXDH, was synthesized and overexpressed in Arabidopsis, the transgenic Arabidopsis showed enhanced salt tolerance. The VvXDH gene was investigated and the results demonstrated the explicit role of VvXDH in conferring salt stress by increasing allantoin accumulation and activating ABA signaling pathway, enhancing ROS scavenging in transgenic Arabidopsis. In addition, the water loss and chlorophyll content loss were reduced in transgenic plants; the transgenic plants showed higher proline level and lower MDA content than that of wild-type Arabidopsis, respectively. In conclusion, the VvXDH gene has the potential to be applied in increasing allantoin accumulation and enhancing the tolerance to abiotic stresses in Arabidopsis and other plants.     

New combinations and typifications in <Emphasis Type="Italic">Bistorta</Emphasis>, <Emphasis Type="Italic">Persicaria</Emphasis>, <Emphasis Type="Italic">Polygonum,</Emphasis> and <Emphasis Type="Italic">Rumex</Emphasis> (Polygonaceae)

New combinations are proposed in anticipation of the Polygonaceae treatment in the forthcoming volume of Intermountain Flora: Polygonum kelloggii var. esotericum, P. kelloggii var. watsonii , Rumex densiflorus var. pycnanthus , R. salicifolius var. utahensis, and R. occidentalis var. tomentellus. Typifications are proposed to facilitate ongoing studies in Polygonaceae and to maintain current usage.     

Drastic anthocyanin increase in response to <Emphasis Type="Italic">PAP1</Emphasis> overexpression in <Emphasis Type="Italic">fls1</Emphasis> knockout mutant confers enhanced osmotic stress tolerance in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Key message

pap1 - D/fls1ko double mutant plants that produce substantial amounts of anthocyanin show tolerance to abiotic stress.

Abstract

Anthocyanins are flavonoids that are abundant in various plants and have beneficial effects on both plants and humans. Many genes in flavonoid biosynthetic pathways have been identified, including those in the MYB-bHLH-WD40 (MBW) complex. The MYB gene Production of Anthocyanin Pigment 1 (PAP1) plays a particularly important role in anthocyanin accumulation. PAP1 expression in many plant systems strongly increases anthocyanin levels, resulting in a dark purple color in many plant organs. In this study, we generated double mutant plants that harbor fls1ko in the pap1-D background (i.e., pap1-D/fls1ko plants), to examine whether anthocyanins can be further enhanced by blocking flavonol biosynthesis under PAP1 overexpression. We also wanted to examine whether the increased anthocyanin levels contribute to defense against osmotic stresses. The pap1-D/fls1ko mutants accumulated higher anthocyanin levels than pap1-D plants in both control and sucrose-treated conditions. However, flavonoid biosynthesis genes were slightly down-regulated in the pap1-D/fls1ko seedlings as compared to their expression in pap1-D seedlings. We also report the performance of pap1-D/fls1ko seedlings in response to plant osmotic stresses.

     

Role of Arabidopsis <Emphasis Type="Italic">ABF1</Emphasis>/<Emphasis Type="Italic">3</Emphasis>/<Emphasis Type="Italic">4</Emphasis> during <Emphasis Type="Italic">det1</Emphasis> germination in salt and osmotic stress conditions

Key message

Arabidopsis det1 mutants exhibit salt and osmotic stress resistant germination. This phenotype requires HY5, ABF1, ABF3, and ABF4.

Abstract

While DE-ETIOLATED 1 (DET1) is well known as a negative regulator of light development, here we describe how det1 mutants also exhibit altered responses to salt and osmotic stress, specifically salt and mannitol resistant germination. LONG HYPOCOTYL 5 (HY5) positively regulates both light and abscisic acid (ABA) signalling. We found that hy5 suppressed the det1 salt and mannitol resistant germination phenotype, thus, det1 stress resistant germination requires HY5. We then queried publically available microarray datasets to identify genes downstream of HY5 that were differentially expressed in det1 mutants. Our analysis revealed that ABA regulated genes, including ABA RESPONSIVE ELEMENT BINDING FACTOR 3 (ABF3), are downregulated in det1 seedlings. We found that ABF3 is induced by salt in wildtype seeds, while homologues ABF4 and ABF1 are repressed, and all three genes are underexpressed in det1 seeds. We then investigated the role of ABF3, ABF4, and ABF1 in det1 phenotypes. Double mutant analysis showed that abf3, abf4, and abf1 all suppress the det1 salt/osmotic stress resistant germination phenotype. In addition, abf1 suppressed det1 rapid water loss and open stomata phenotypes. Thus interactions between ABF genes contribute to det1 salt/osmotic stress response phenotypes.