A DESD-box helicase functions in salinity stress tolerance by improving photosynthesis and antioxidant machinery in rice (Oryza sativa L. cv. PB1)

The exact mechanism of helicase-mediated salinity tolerance is not yet understood. We have isolated a DESD-box containing cDNA from Pisum sativum (Pea) and named it as PDH45. It is a unique member of DEAD-box helicase family; containing DESD instead of DEAD/H. PDH45 overexpression driven by constitutive cauliflower mosaic virus-35S promoter in rice transgenic [Oryza sativa L. cv. Pusa Basmati 1 (PB1)] plants confers salinity tolerance by improving the photosynthesis and antioxidant machinery. The Na⁺ ion concentration and oxidative stress parameters in leaves of the NaCl (0, 100 or 200 mM) treated PDH45 overexpressing T₁ transgenic lines were lower as compared to wild type (WT) rice plants under similar conditions. The 200 mM NaCl significantly reduced the leaf area, plant dry mass, net photosynthetic rate (P_N), stomatal conductance (gs), intercellular CO₂ (Ci), chlorophyll (Chl) content in WT plants as compared to the transgenics. The T₁ transgenics exhibited higher glutathione (GSH) and ascorbate (AsA) contents under salinity stress. The activities of antioxidant enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and glutathione reductase (GR) were significantly higher in transgenics; suggesting the existence of an efficient antioxidant defence system to cope with salinity induced-oxidative damage. Yeast two-hybrid assay indicated that the PDH45 protein interacts with Cu/Zn SOD, adenosine-5′-phosphosulfate-kinase, cysteine proteinase and eIF(4G), thus confirming the involvement of ROS scavenging machinery in the transgenic plants to provide salt tolerance. Furthermore, the T₂ transgenics were also able to grow, flower, and set viable seeds under continuous salinity stress of 200 mM NaCl. This study provides insights into the mechanism of PDH45 mediated salinity stress tolerance by controlling the generation of stress induced reactive oxygen species (ROS) and also by protecting the photosynthetic machinery through a strengthened antioxidant system.     

Pea DNA helicase 45 promotes salinity stress tolerance in IR64 rice with improved yield

The helicases provide duplex unwinding function in an ATP-dependent manner and thereby play important role in almost all the nucleic acids transaction. Since stress reduces the protein synthesis by affecting the cellular gene expression machinery, so it is evident that molecules involved in nucleic acid processing including translation factors/helicases are likely to be affected. Earlier pea DNA helicase 45 (PDH45), a homolog of translation initiation factor 4A (eIF4A) was reported to play important role in salinity stress tolerance in tobacco and Bangladeshi rice variety Binnatoa. We report here the overexpression of PDH45 gene in the indica rice variety IR64, via Agrobacterium-mediated transformation. Molecular analysis of the transgenics revealed stable integration of the transgene in the T1 generation. Enhanced tolerance to salinity was observed in the plants transformed with PDH45 gene. Better physiological and yield performances including endogenous nutrient contents (N, P, K, Na) of the transgenics under salt treatment were observed as compared with wild type (WT), vector control and antisense transgenics. All these results indicated that the overexpression of PDH45 in the IR64 rice transgenics enable them to perform better with enhanced salinity stress tolerance and improved physiological traits. Based on the homology of PDH45 protein with eIF4A protein we suggest that it may act at the translational level to enhance or stabilize protein synthesis under stress conditions.     

Ectopic expression of ADP ribosylation factor 1 (SaARF1) from smooth cordgrass (Spartina alterniflora Loisel) confers drought and salt tolerance in transgenic rice and Arabidopsis

Salinity and drought are two very important abiotic stressors that negatively impact the growth and yield of all sensitive crop plants. Genes from halophytes have been shown to be useful to engineer crop plants that can survive under adverse soil and water conditions. The present report establishes, for the first time, the physiological role of a class one ADP ribosylation factor gene (SaARF1) from the halophyte Spartina alterniflora (smooth cordgrass) in imparting salinity and drought stress tolerance when expressed in both monocot (rice) and dicot (Arabidopsis) systems. The Arabidopsis and rice plants overexpressing ARF1 are many-fold more tolerant to salt and drought than wild-type (WT) plants. The transgenics exhibited improved growth and productivity relative to WT through tissue tolerance by maintaining higher relative water content and membrane stability, and higher photosynthetic yield by retaining higher chlorophyll concentration and fluorescence under stress conditions compared to WT. These findings indicated that genes from halophyte resources can be useful to engineer and improve salt and drought stress tolerance in both monocot and dicot plants.     

Abiotic stress tolerance in transgenic eggplant (Solanum melongena L.) by introduction of bacterial mannitol phosphodehydrogenase gene

In the present work, the bacterial mannitol-1-phosphodehydrogenase(mtlD) gene was introduced into eggplant(Solanummelongena L.) by Agrobacteriumtumefaciens-mediated transformation. Several transformants weregenerated and the transgene integration was confirmed by PCR, dot blot andSouthern blot analysis. Transgenic lines of T₀ and T₁generations were examined for tolerance to NaCl-induced salt stress,polyethylene glycol-mediated drought and chilling stress under bothinvitro and in vivo growth conditions. Aconsiderable proportions of transgenic seeds germinated and seedlings grew wellon 200 mM salt-amended MS basal medium, whereas seeds ofuntransformed control plants failed to germinate. Further, leaf explants fromthe transgenics could grow and showed signs of shoot regeneration onsalt-amended MS regeneration medium, whereas wild type did not respond, and infact the explants showed necrosis and loss of chlorophyll after about one week.The transgenic leaves could also withstand desiccation, and transgenics couldgrow well under chilling stress, and hydroponic conditions with salt stress ascompared to wild type plants. Thus, the transgenic lines were found to betolerant against osmotic stress induced by salt, drought and chilling stress.The morphology of the transgenic plants was normal as controls, but thechlorophyll content was higher in some of the lines. These observations suggestthat mtlD gene can impart abiotic stress tolerance ineggplant.     

Overexpression of osmotin gene confers tolerance to salt and drought stresses in transgenic tomato (Solanum lycopersicum L.)

Abiotic stresses, especially salinity and drought, are major limiting factors for plant growth and crop productivity. In an attempt to develop salt and drought tolerant tomato, a DNA cassette containing tobacco osmotin gene driven by a cauliflower mosaic virus 35S promoter was transferred to tomato (Solanum lycopersicum) via Agrobacterium-mediated transformation. Putative T0 transgenic plants were screened by PCR analysis. The selected transformants were evaluated for salt and drought stress tolerance by physiological analysis at T1 and T2 generations. Integration of the osmotin gene in transgenic T1 plants was verified by Southern blot hybridization. Transgenic expression of the osmotin gene was verified by RT-PCR and northern blotting in T1 plants. T1 progenies from both transformed and untransformed plants were tested for salt and drought tolerance by subjecting them to different levels of NaCl stress and by withholding water supply, respectively. Results from different physiological tests demonstrated enhanced tolerance to salt and drought stresses in transgenic plants harboring the osmotin gene as compared to the wild-type plants. The transgenic lines showed significantly higher relative water content, chlorophyll content, proline content, and leaf expansion than the wild-type plants under stress conditions. The present investigation clearly shows that overexpression of osmotin gene enhances salt and drought stress tolerance in transgenic tomato plants.     

Alleviation of Drought Stress in Turfgrass by the Combined Application of Nano-compost and Microbes from Compost

Drought stress is a key environmental factor limiting the growth and productivity of plants. Turfgrasses are often affected by drought in north China due to water shortage. In the present study, the impact of nanosized compost either alone or in combination with drought tolerant isolates from compost on turfgrass response to drought was investigated. Municipal solid waste (MSW) compost was processed into nanosized particles and added in turfgrass soil. Microorganisms in the MSW compost were screened for drought stress tolerance using increasing concentrations of polyethylene glycol (PEG 6000). Festuca arundinacea Schreb. plants were inoculated with this mixture and exposed to drought stress by reducing the amount of water added at vegetative growth stage. The drought-tolerant isolates from compost were identified as Bacillus cereus, Lysinibacillus sp. and Rhodotorula glutinis. Our results revealed that nanocompost and microbial inoculation minimized the drought stress-imposed effects significantly increasing shoot biomass, root biomass, and chlorophyll content. Similarly, nanocompost-treated and inoculated seedlings showed higher levels of antioxidant enzymes and lower MDA content compared to nontreated control under drought stress. The combination of nano-sized compost and microbial inoculation were more efficient than nanocompost alone in terms of influencing growth and physiological status of the seedlings under drought stress. Our data suggest that nanocompost combined with drought-tolerant isolates may enhance drought tolerance in turfgrass by promoting plant growth and increasing the capacity to eliminate toxic reactive oxygen species (ROS).     

Drought tolerance and proteomics studies of transgenic wheat containing the maize C<Subscript>4</Subscript> phosphoenolpyruvate carboxylase (<Emphasis Type="Italic">PEPC</Emphasis>) gene

Enhancing drought tolerance of crops has been a great challenge in crop improvement. Here, we report the maize phosphoenolpyruvate carboxylase (PEPC) gene was able to confer drought tolerance and increase grain yield in transgenic wheat (Triticum aestivum L.) plants. The improved of drought tolerance was associated with higher levels of proline, soluble sugar, soluble protein, and higher water use efficiency. The transgenic wheat plants had also a more extensive root system as well as increased photosynthetic capacity during stress treatments. The increased grain yield of the transgenic wheat was contributed by improved biomass, larger spike and grain numbers, and heavier 1000-grain weight under drought-stress conditions. Under non-stressed conditions, there were no significant increases in these of the measured traits except for photosynthetic rate when compared with parental wheat. Proteomic research showed that the expression levels of some proteins, including chlorophyll A-B binding protein and pyruvate, phosphate dikinase, which are related to photosynthesis, PAP fibrillin, which is involved in cytoskeleton synthesis, S-adenosylmethionine synthetase, which catalyzes methionine synthesis, were induced in the transgenic wheat under drought stress. Additionally, the expression of glutamine synthetase, which is involved in ammonia assimilation, was induced by drought stress in the wheat. Our study shows that PEPC can improve both stress tolerance and grain yield in wheat, demonstrating the efficacy of PEPC in crop improvement.     

Screening for drought tolerance in mutant germplasm of sesame (Sesamum indicum) probing by chlorophyll a fluorescence

Drought is one of the major constraints limiting crop productivity in African Sahel. The aim of this study was to select mutant sesame (Sesamum indicum L.) lines with improved levels of drought resistance. Twenty-one M4-M5 sesame lines of unknown drought tolerance, and their three parental sources with well-known and contrasting drought tolerance levels were evaluated at the vegetative stage in a factorial pot experiment, using a completely randomized design with three replicates. After 2 weeks of growth, water was withheld for 16 days as drought stress treatment. Chlorophyll a fluorescence data, as well as stomatal conductance and flag leaf temperature were recorded during the stress period. Recorded chlorophyll a fluorescence transients were analyzed by the JIP-test to translate stress-induced damage in these transients to changes in biophysical parameters allowing quantification of the energy flow through the photosynthetic apparatus. Large genotypic differences in the extent to which drought stress affected chlorophyll a fluorescence transients were observed. Drought stress reduced the performance index and stomatal conductance, and increased flag leaf temperature but had little effect on maximum quantum yield of primary photochemistry. A drought factor index is proposed in this work to screen for improved drought tolerance in twenty-one M4-M5 sesame lines. Mutant lines shi165, lc162, mc112, lc164, icn115, icn141, mt169, dwf172 and cc102 exhibited drought factor index values superior to those of the known drought tolerant cultivars Birkan and 38-1-7. A significant and negative relationship was found between the drought factor index and the leaf temperature index. Finally, we succeeded in obtaining drought tolerant lines with good secondary traits by using mutagenesis and chlorophyll fluorescence technique.     

Comparative effect of water, heat and light stresses on photosynthetic reactions in Sorghum bicolor(L.) Moench

Five varieties of Sorghum bicolor (L.) Moench., differing in their drought tolerance under field conditions have been used to study the effect of individual components of drought stress, namely high light intensity stress, heat stress and water stress, on their photosynthetic performance. Chlorophyll content, chlorophyll fluorescence, ribulose-1,5-bisphosphate carboxylase (Rubisco, EC 4.1.1.39) content, phosphoenolpyruvate carboxylase (PEPcase, EC 4.1.1.31) activity and photo-synthetic oxygen evolution were used as key parameters to assess photosynthetic performance. The results indicated that photochemical efficiency of photosystem II (PSII) was severely reduced by all three stress components, whereas PEPcase activity was more specifically reduced by water stress. Degradation of Rubisco and chlorophyll loss occurred under high light and water stress conditions. Of the four drought-tolerant varieties, E 36-1 showed higher PEPcase activity, Rubisco content and photochemical efficiency of PSII, and was able to sustain a higher maximal rate of photosynthetic oxygen evolution under each stress condition as compared to the other varieties. A high stability to stress-induced damage, or acclimation of photosynthesis to the individual components of drought stress may contribute to the high yields of E 36-1 under drought conditions. In the E 36-1 variety markedly higher levels of the chloroplastic chaperonin 60 (cpn 60) were observed under all stress conditions than in the susceptible variety CSV 5.Key words: Chlorophyll fluorescence, drought stress, oxygen evolution, phosphoenopyruvate carboxylase, Sorghum.