Computational analysis and expression profiling of potassium transport-related gene families in mango (Mangifera indica) indicate their role in stress response and fruit development.

While involved in a functional genomics program, we found that the overexpression of potato (Solanum tuberosum) glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene in yeast improves its water-deficit stress (drought) tolerance. But, the effect of altered (under and over) expression of GAPDH on water-deficit stress tolerance of higher plants is not yet studied. In this study, we used a versatile reverse genetics tool called virus-induced gene silencing and down-regulated the expression of GAPDH gene in tobacco (Nicotiana benthamiana) to examine the relevance (effect of underexpression) of GAPDH on drought tolerance of higher plants. Leaf discs made from silenced and nonsilenced tobacco plants were subjected to water-deficit stress. Measure of cell viability and the content of chlorophyll in stressed and nonstressed leaf discs were determined to quantify the effect of stress. Leaf discs made from the gene-silenced plants were found to be more severely affected by the stress than the leaf discs made from nonsilenced plants, implying the importance of GAPDH gene in drought tolerance of plants. Furthermore, to reiterate the involvement of GAPDH in drought tolerance of plants, potato transgenic plants constitutively overexpressing the GAPDH gene were generated and their performance under drought condition was analyzed. Transgenic potato plants showed improved drought tolerance when compared to wild-type potato. On the whole, our results confirm that the GAPDH gene plays an important role in drought tolerance of higher plants, and its constitutive overexpression by genetic engineering can be used to improve drought tolerance of crop plants like potato.

Nicotiana tabacum L. ‘Glurk’ plants were transformed with antiapoptotic animal genes [chicken Bcl-xl; nematode CED-9; chicken Bcl-xl(GA) a mutant of Bcl-xl ; and a 3’ non-coding region of human Bcl-2, referred to as 161-1]. Our objectives were to determine whether plant transformation with anti-apoptotic genes ameliorates drought tolerance in tobacco plants by subjecting the plants to a dry-down period. The non-transformed Glurk and the transgenic Glurk harboring G115, which expresses β-glucuronidase, served as controls. Transformation of tobacco plants with animal anti-apoptotic genes significantly impacted the rates of photosynthesis (A) and stomatal conductance (gs), but not to the same extent in every line. Controls generally exhibited higher A and gs than the transformed plants under well-watered conditions. Photosynthesis and stomatal conductance declined significantly on the 3rd day, and approached zero on the 11th day of water deprivation. Differences among controls and transformed tobacco plants disappeared as soil moisture deficit increased. Relative water content (RWC) and leaf water potential (ψw) remained relatively high in the first 3 d of water deprivation, while a dramatic reduction occurred in all plants on the 6th day. Relative water content did not differ between controls and transformed plants. Water potential declined significantly (became more negative) with the increase in soil moisture deficit. Evident differences among transformed and control plants appeared on the 6th day of water deprivation. The controls, Glurk and G115 generally maintained a higher water potential between days 6 and 11 compared to the transformed tobacco plants. Osmotic adjustment occurred in transformed plants but not in the controls, in response to drought. Relative water content at turgor loss point (RWCtlp) and osmotic potential at turgor loss point (ψπtlp) provided a measure of drought tolerance in plants. G115, Glurk and Bcl-xl plants lost turgor at a higher relative water content than Bcl-xl(GA), CED-9 and 161-1. ψπtlp in the controls G115 and Glurk were relatively higher compared to the transformed plants. We concluded that transgenic plants with anti-apoptotic genes resulted in moderate amelioration of drought tolerance in tobacco plants. Key words: Anti-apoptotic genes, programmed cell death, genetic engineering, Nicotiana tabaccum, drought tolerance, gas exchange, photosynthesis, turgor, osmotic adjustment

Research on plant growth-promoting bacteria (PGPR) revealed an effective role of bacterial volatile organic compounds (VOCs) in stress alleviation. Out of 15 PGPR strains, infection with VOCs from Pseudomonas pseudoalcaligenes' resulted in maximum germination, growth promotion, and drought tolerance in maize plants. The VOCs of P. pseudoalcaligenes caused induced systemic tolerance in maize plants during 7 days of drought stress. The VOCs exposed plants displayed resistance to drought stress by reducing electrolyte leakage and malondialdehyde content and increasing the synthesis of photosynthetic pigments, proline, and phytohormones contents. Maize plants revealed enhanced resistance by showing higher activities of antioxidant defense enzymes both in shoots and roots under drought stress. Activities of antioxidant enzymes were more pronounced in shoots than roots. Gas chromatography and mass spectrophotometric (GC-MS) analysis comparing VOCs produced by the most efficient P. pseudoalcaligenes strain and inefficient strains of Pseudomonas sp. grown in culture media revealed nine compounds that they had in common. However, dimethyl disulfide, 2,3-butanediol, and 2-pentylfuran were detected only in P. pseudoalcaligenes, indicating these compounds are potential candidates for drought stress induction. Further studies are needed to unravel the molecular mechanisms of VOCs-mediated systemic drought tolerance in plants related to each identified VOC.

The widely distributed heat shock protein DnaJ is renowned for its pivotal role in enhancing thermal tolerance in plants; however, its involvement in drought tolerance remains elusive. In this study, genes encoding DnaJ1 were cloned from drought-resistant wild tomato (Solanum pennellii) and drought-sensitive cultivated tomato (Solanum lycopersicum). SpDnaJ1 and SlDnaJ1 from both tomato species were localized in the chloroplast, and their gene expression was induced by various abiotic stresses. SpDnaJ1 was found to be a more potent regulator than SlDnaJ1 in oxidative stress tolerance when expressed in yeast cells. Overexpression of SpDnaJ1 was demonstrated to confer drought tolerance in transgenic plants of cultivated tomato. These transgenic plants exhibited reduced relative conductivity, leaf water loss rate, and malondialdehyde content as compared to the wild-type plants following drought treatment. RNA-seq analysis revealed that overexpression of SpDnaJ1 primarily affects the expression of genes associated with antioxidants, protease inhibitors, and MAPK signaling in response to drought stress. Screening of a tomato cDNA library in the yeast two-hybrid system identified a flavanone 3-hydroxylase-like protein (F3HL) as an interacting protein of DnaJ1. Subsequent findings revealed that F3HL enhances drought tolerance in tomato by increasing the activity of antioxidant enzymes and scavenging reactive oxygen species. These findings demonstrate a pivotal role of DnaJ1-F3HL interaction in enhancing drought tolerance, unveiling a novel molecular mechanism in drought tolerance in plants.

Mango Anthracnose: Economic Impact and Current Options For Integrated Managaement.

Nitric oxide (NO), a key signaling molecule, can be induced by polyamines (PAs), which play an important role in improving drought tolerance in plants. This study was to further investigate the role of NO in spermidine (Spd)-induced drought tolerance associated with antioxidant defense in leaves of white clover (Trifolium repens) under drought stress induced by -0.3MPa polyethylene glycol (PEG-6000) solution. A hydroponic growth method was used for cultivating plants in a controlled growth chamber for 30-33days until the second leaves were fully expanded. Two relative independent experiments were carried out in our study. One is that exogenous application of Spd or an NO donor (sodium nitroprusside (SNP)) significantly improved drought tolerance in whole plants, as demonstrated by better phenotypic appearance, increased relative water content (RWC), and decreased electrolyte leakage (EL) and malondialdehyde (MDA) content in leaves as compared to untreated plants. For another detached leaf experiment, PEG induced an increase in the generation of NO in cells and significantly improved activities of nitrate reductase (NR) and nitric oxide synthase (NOS). These responses could be blocked by pre-treatment with a Spd biosynthetic inhibitor, dicyclohexyl amine (DCHA), and then reversed by application of exogenous Spd. Meanwhile, PEG induced up-regulation of activities and gene transcript levels of corresponding antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) to varying degrees, while these effects were partially blocked by pre-treatment with DCHA, the scavenger of NO, the inhibitors of NR or NOS. In addition, Spd-induced antioxidant enzyme activities and gene expression also could be effectively inhibited by an NO scavenger as well as inhibitors of NR and NOS. These findings suggest that both Spd and NO can enhance drought tolerance. Spd was involved in drought stress-activated NR and NOS pathways associated with NO release, which mediated antioxidant defense and thus contributed to drought tolerance in white clover.

Dwarfism and drought tolerance are 2 valuable traits in breeding of many crops. In this study, we report the novel physiological roles of cholesterol in regulation of plant growth and drought tolerance. Compared with the wild type, sterol-C24-methyltransferase 1 (SMT1) gene transcript was greatly reduced in a bermudagrass mutant with dwarfism and enhanced drought tolerance, accompanied with cholesterol accumulation, elevated transcript levels of a small group of genes including SAMDC, and increased concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm). Knock-down of OsSMT1 expression by RNA interference resulted in similar phenotypic changes in transgenic rice. Moreover, exogenously applied cholesterol also led to elevated transcripts of a similar set of genes, higher levels of Put, Spd, and Spm, improved drought tolerance, and reduced plant height in both bermudagrass and rice. We revealed that it is Spm, but not Spd, that is responsible for the height reduction in bermudagrass and rice. In conclusion, we suggest that cholesterol induces expression of SAMDC and leads to dwarfism and elevated drought tolerance in plants as a result of the promoted Spd and Spm synthesis.

Plant responses and adaptations to a changing climate.

Drought stress in plants has become one of the major abiotic stress that limits the growth and development of plants which also contributes to low yields. Biotechnology which has new and emerging techniques can be use to solve the problem of drought stress in plants. This review aimed at identifying drought stress tolerance in plants at different stages, how plants respond to drought stress using different methods and the application of different biotechnology methods to improve drought tolerance in plants. Some important parameters about drought stress in plants such as drought tolerance mechanisms, plants responses to drought stress, gene regulation for drought stress tolerance in plants, effects of drought stress at different stages of plant growth and biotechnology methods in developing drought tolerance in plants was reviewed. The use of biotechnology methods such as classical breeding, use of genetic manipulation, genes from resurrection plants and Protoplast fusion was discussed. Drought stress affects our plants seriously and it leads to wilts, reduction of yields and death of plants at different developmental stages. Plants have developed different mechanisms to respond to drought stress but these mechanisms are not sufficient enough without the application of biotechnology to greatly improve the growth, development and increase yield in pants. The use of biotechnology greatly improves plants ability to tolerate drought stress depending on the plant species and period of exposure. The use of biotechnology methods has become very vital in improving plants drought stress so as to overcome the major problems of plants which includes increase in population and climatic change.

Increasing cuticular wax accumulation in plants has been associated with improving drought tolerance in plants. In this study, a cDNA clone encoding the SlSHN1 transcription factor, the closest ortholog to WIN/SHN1 gene in Arabidopsis, was isolated from tomato plant. Expression analysis of SlSHN1 indicated that it is induced in response to drought conditions. The over-expression of SlSHN1 in tomato under the control of the constitutive CaMV 35S promoter produced plants that showed mild growth retardation phenotype with shiny and dark green leaves. Scanning electron microscopy showed that the over-expression of SlSHN1 in tomato resulted in higher cuticular wax deposition on leaf epidermial tissue when compared to non-transformed plants. Expression analysis in transgenic lines over-expressing SlSHN1 indicated that several wax-related synthesis genes were induced. Transgenic tomato plants over-expressing SlSHN1 showed higher drought tolerance when compared with wild type plants; this was reflected in delayed wilting of transgenic lines, improved water status and reduced water loss rate when compared with wild type plants. In conclusion, the SlSHN1 gene can modulate wax accumulation and could be utilized to enhance drought tolerance in tomato plant.

Mycorrhizas are known to improve host plant nutritional status as a consequence of water transport from the soil to the host plant through the external mycelium as a direct effect or improved host plant nutrition primarily, phosphorus as an indirect effect. The direct hyphal water transport is quantified to be meager and a major part of the benefits of mycorrhizal symbiosis is indirect and nutritionally related. In arid and semi-arid regions where drought occurrence is very frequent and soil moisture content is highly restricted, mycorrhizas can assist in exploiting the soil beyond the rhizosphere that helps the host plant to withstand drought stress conditions. The drought tolerance in mycorrhiza-inoculated plants is quite complex and such response is due to a series of processes such as improved nitrogen (N) availability in soils, extensive root surface area and cationic exchange capacity, collective N assimilatory pathways in plant-mycorrhizal system, luxuriant uptake of nutrients besides remobilization of nutrients to support grain growth. These physiological, biochemical, nutritional and morphological changes in the mycorrhizas associated host plants have contributed to the ability of the host plants to survive under limited water environments. Despite mycorrhiza-assisted and N nutritionally enabled host plant drought tolerance is evident, more research is required to gain insights into the mechanisms involved. This review highlights the role of mycorrhizas on N dynamics in the rhizosphere and enhanced host plant N nutrition that collectively contributes to the sustained crop productivity under drought stress conditions.

The phytohormone abscisic acid (ABA) is important during abiotic stresses, especially drought stress. Although mitogen-activated protein kinase (MAPK) cascades are crucial for ABA-mediated drought tolerance, how these cascades integrate and deliver the downstream ABA signals is poorly understood. Here, the group C MAPK GhMPK7 was found to positively regulate ABA-mediated drought tolerance in cotton. Silencing GhMPK7 decreased drought tolerance in transgenic cotton plants. After ABA treatment, the GhMPK7-silenced transgenic plants were not sensitive to ABA, exhibited restricted stomatal closure, faster germination rates and longer roots. Importantly, GhSDIRIP1, a negative regulator of ABA signaling, was found to interact with GhMPK7 as a downstream. Silencing GhSDIRIP1 in GhMPK7-silenced transgenic cotton plants restored the drought-intolerant phenotype caused by GhMPK7 silencing. The results of the phosphorylation experiments revealed that GhMPK7 can phosphorylate the Ser-19 residue of GhSDIRIP1 to regulate its stability. GhMPK7-induced GhSDIRIP1 protein degradation increased ABA signaling intensity in response to drought stress. Overall, our findings provide insights into the positive regulatory mechanism of ABA-involved drought tolerance, which is mediated by the GhMPK7-GhSDIRIP1 module. This study expands our knowledge of how MAPK cascades regulate the intensity of ABA-mediated drought tolerance in plants and advances our understanding of the interplay between phosphorylation and ubiquitination.

Drought is one of the major constraints for sustainable crop production worldwide, especially in arid and semiarid regions. The global warming and climate change scenario has worsened the dilemma of water scarcity, creating an immediate threat to food security. Conserving water resources and exploiting various strategies that enable plants to withstand water deficits need to be urgently addressed. Drought adversely affects plant growth by modulating a range of physio-chemical, metabolic, and molecular processes inside the plant body, which ultimately reduces crop productivity. Besides developing drought-tolerant cultivars, better nutrient management could be a promising strategy to enhance drought tolerance in crop plants. Silicon, a quasi-essential element, is known to play a vital role in improving crop performance under a range of biotic and abiotic stresses. This review discusses the potential of Si application in attenuating the adverse effects of water-deficit stress. Silicon enhances plant growth by improving seed germination, cell membrane stability, carbon assimilation, plant–water relations and osmotic adjustment (by accumulating soluble sugars, proline and glycine betaine). It triggers the activity of antioxidants, promotes the biosynthesis of phytohormones, enhances nutrient acquisition and regulates the activity of vital enzymes in plants under drought stress. Silicon also induces anatomical changes in the plant cell wall through the deposition of polymerized amorphous silica (SiO2-nH2O), thereby improving stem and leaf erectness and reducing lodging. Further, Si-mediated physiological, biochemical and molecular mechanisms associated with drought tolerance in plants and future research prospects have been elucidated.

Background. The study of the molecular mechanisms regulating gene expression in response tovarioustypes of stress in woody plants,particularlydrought and high soil salinity,is becominganecessary condition for breeding orcreatingnew resistant cultivars, forms, and hybrids withspecificeconomically valuabletraits.Currently, the extent and depth of studying the genes involved in drought and high soil salinity tolerance in woody plants is extremely low compared to agricultural crops, which significantly complicates and slows down the breeding process that should be based on achievements in molecular biology and genetics. Purpose. To summarize, describe, and select potential genes involved in the formation of drought and salt tolerance in a range of woody plants used in agroforestry and protective afforestation, growing in areas with arid and semi-arid climates. Materials and methods. To achieve the research objectives, more than250 scientific sources were reviewed and a search in open gene databases was conducted to identify genes and their homologues databases using the BLAST program associated with drought and salt tolerance in woody plants used in agroforestry and protective afforestation. Results. This study summarizes and describes 28 genes associated with drought tolerance and 14 genes associated with salt tolerance in the genera Quercusand Populus, and the families Fabaceae, Rosaceae, and Oleaceae. Conclusion. Thus, as a result of the analysis of genes associated with drought and salt tolerance in woody plants, key targets have been identified that can serve as a basis for molecular selection, followed by the identification of potential markers and their possible association with economically valuabletraits.

Drought is one of the key restraints to agricultural productivity worldwide and is expected to increase further. Drought stress accompanied by reduction in precipitation pose major challenges to future food safety. Strategies should be develop to enhance drought tolerance in crops like chickpea and wheat, in order to enhance their growth and yield. Drought tolerance strategies are costly and time consuming however, recent studies specify that plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can help plants to withstand under harsh environmental condition and enable plants to cope with drought stress. PGPR can act as biofertilizer and bioenhancer for different legumes and non-legumes. The use of PGPR and symbiotic microorganisms, may be valuable in developing strategies to assist water conservation in plants. The use of PGPR has been confirmed to be an ecologically sound way of enhancing crop yields by facilitating plant growth through direct or indirect mechanism. The mechanisms of PGPR for water conservation include secretion of exopolysaccharides, biofilm formation, alternation in phytohormone content, improvement in sugar concentration, enhancing availability of micro- and macronutrients and changes in plant functional traits. Similarly, plant growth regulators (PGRs) are specially noticed in actively growing tissues under stress conditions and have been associated in the control of cell division, embryogenesis, root formation, fruit development and ripening, and reactions to biotic and abiotic stresses and upholding water conservation status in plants. Previous studies also suggest that plant metabolites interact with plant physiology under stress condition and impart drought tolerance. Metabolites like, sugars, amino acids, organic acid and polyols play a key role in drought tolerance of crop plants grown under stress condition. It is concluded from the present study that PGRs in combination with PGPR consortium can be an effective formulation to promote plant growth and maintenance of plant turgidity under drought stress. This review is a compilation of the effect of drought stress on crop plants and described interactions between PGPR/PGRs and plant development, knowledge of water conservation and stress release strategies of PGPR and PGRs and the role of plant metabolites in drought tolerance of crop plants. This review also bridges the gaps that summarizes the mechanism of action of PGPR for drought tolerance of crop plants and sustainability of agriculture and applicability of these beneficial rhizobacteria in different agro-ecosystems under drought stress.