Stress tolerance and glucose insensitive phenotypes in Arabidopsis overexpressing the CpMYB10 transcription factor gene

PpMYB105 inhibits chilling injury by regulating PpMsrA1 in peach fruit

KEY MESSAGE

MeJA supplementation enhanced the chilling tolerance and gene expression of PpMsrA1. PpMYB105 protein positively regulated the PpMsrA1 promoter. PpMYB105 mediated the MeJA-boosted chilling tolerance by regulating PpMsrA1. Cold storage can maintain the quality of postharvest fruit. However, peaches easily suffer from chilling injury (CI) during cold storage, leading to economic loss. Results showed that methyl jasmonate (MeJA) supplementation reduced the CI severity, and enhanced the gene expression of methionine sulfoxide reductase A1 (PpMsrA1). It was found that MeJA application elevated the MsrA activity and methionine (Met) content, and reduced the methionine-S-sulfoxide (Met-S-SO) content and reactive oxygen species (ROS) production afterwards. Moreover, PpMYB105 could activate the transcription of PpMsrA1 by binding to the MYB binding element in its promoter. The gene expression of PpMYB105 was up-regulated by MeJA application. Overexpression of PpMYB105 in tomatoes enhanced the chilling tolerance and gene expression of SlMsrA1. Virus-induced gene silencing of PpMYB105 in peaches resulted in the increase in CI severity and the decrease in gene expression of PpMsrA1. Thus, PpMYB105 was involved in the MeJA-boosted chilling tolerance by regulating PpMsrA1.

Ectopic over-expression of HaFT-1, a 14-3-3 protein from Haloxylon ammodendron, enhances acquired thermotolerance in transgenic Arabidopsis

Haloxylon ammodendron, an important shrub utilized for afforestation in desert areas, can withstand harsh ecological conditions such as drought, high salt and extreme heat. A better understanding of the stress adaptation mechanisms of H. ammodendron is vital for ecological improvement in desert areas. In this study, the role of the H. ammodendron 14-3-3 protein HaFT-1 in thermotolerance was investigated. qRT-PCR analysis showed that heat stress (HS) priming (the first HS) enhanced the expression of HaFT-1 during the second HS and subsequent recovery phase. The subcellular localization of YFP-HaFT-1 fusion protein was mainly detected in cytoplasm. HaFT-1 overexpression increased the germination rate of transgenic Arabidopsis seeds, and the survival rate of HaFT-1 overexpression seedlings was higher than that of wild-type (WT) Arabidopsis after priming-and-triggering and non-primed control treatments. Cell death staining showed that HaFT-1 overexpression lines exhibited significantly reduced cell death during HS compared to WT. Transcriptome analysis showed that genes associated with energy generation, protein metabolism, proline metabolism, autophagy, chlorophyll metabolism and reactive oxygen species (ROS) scavenging were important to the thermotolerance of HS-primed HaFT-1 transgenic plants. Growth physiology analysis indicated that priming-and-triggering treatment of Arabidopsis seedlings overexpressing HaFT-1 increased proline content and strengthened ROS scavenging activity. These results demonstrated that overexpression of HaFT-1 increased not only HS priming but also tolerance to the second HS of transgenic Arabidopsis, suggesting that HaFT-1 is a positive regulator in acquired thermotolerance.

Pseudocrossidium replicatum (Taylor) R.H. Zander is a fully desiccation-tolerant moss that expresses an inducible molecular mechanism in response to severe abiotic stress

KEY MESSAGE

The moss Pseudocrossidium replicatum is a desiccation-tolerant species that uses an inducible system to withstand severe abiotic stress in both protonemal and gametophore tissues. Desiccation tolerance (DT) is the ability of cells to recover from an air-dried state. Here, the moss Pseudocrossidium replicatum was identified as a fully desiccation-tolerant (FDT) species. Its gametophores rapidly lost more than 90% of their water content when exposed to a low-humidity atmosphere [23% relative humidity (RH)], but abscisic acid (ABA) pretreatment diminished the final water loss after equilibrium was reached. P. replicatum gametophores maintained good maximum photosystem II (PSII) efficiency (Fv/Fm) for up to two hours during slow dehydration; however, ABA pretreatment induced a faster decrease in the Fv/Fm. ABA also induced a faster recovery of the Fv/Fm after rehydration. Protein synthesis inhibitor treatment before dehydration hampered the recovery of the Fv/Fm when the gametophores were rehydrated after desiccation, suggesting the presence of an inducible protective mechanism that is activated in response to abiotic stress. This observation was also supported by accumulation of soluble sugars in gametophores exposed to ABA or NaCl. Exogenous ABA treatment delayed the germination of P. replicatum spores and induced morphological changes in protonemal cells that resembled brachycytes. Transcriptome analyses revealed the presence of an inducible molecular mechanism in P. replicatum protonemata that was activated in response to dehydration. This study is the first RNA-Seq study of the protonemal tissues of an FDT moss. Our results suggest that P. replicatum is an FDT moss equipped with an inducible molecular response that prepares this species for severe abiotic stress and that ABA plays an important role in this response.

What Do We Know About the Genetic Basis of Seed Desiccation Tolerance and Longevity?

Long-term seed storage is important for protecting both economic interests and biodiversity. The extraordinary properties of seeds allow us to store them in the right conditions for years. However, not all types of seeds are resilient, and some do not tolerate extreme desiccation or low temperature. Seeds can be divided into three categories: (1) orthodox seeds, which tolerate water losses of up to 7% of their water content and can be stored at low temperature; (2) recalcitrant seeds, which require a humidity of 27%; and (3) intermediate seeds, which lose their viability relatively quickly compared to orthodox seeds. In this article, we discuss the genetic bases for desiccation tolerance and longevity in seeds and the differences in gene expression profiles between the mentioned types of seeds.

Crassulacean Acid Metabolism Abiotic Stress-Responsive Transcription Factors: a Potential Genetic Engineering Approach for Improving Crop Tolerance to Abiotic Stress

This perspective paper explores the utilization of abiotic stress-responsive transcription factors (TFs) from crassulacean acid metabolism (CAM) plants to improve abiotic stress tolerance in crop plants. CAM is a specialized type of photosynthetic adaptation that enhances water-use efficiency (WUE) by shifting CO2 uptake to all or part of the nighttime when evaporative water losses are minimal. Recent studies have shown that TF-based genetic engineering could be a useful approach for improving plant abiotic stress tolerance because of the role of TFs as master regulators of clusters of stress-responsive genes. Here, we explore the use of abiotic stress-responsive TFs from CAM plants to improve abiotic stress tolerance and WUE in crops by controlling the expression of gene cohorts that mediate drought-responsive adaptations. Recent research has revealed several TF families including AP2/ERF, MYB, WRKY, NAC, NF-Y, and bZIP that might regulate water-deficit stress responses and CAM in the inducible CAM plant Mesembryanthemum crystallinum under water-deficit stress-induced CAM and in the obligate CAM plant Kalanchoe fedtschenkoi. Overexpression of genes from these families in Arabidopsis thaliana can improve abiotic stress tolerance in A. thaliana in some instances. Therefore, we propose that TF-based genetic engineering with a small number of CAM abiotic stress-responsive TFs will be a promising strategy for improving abiotic stress tolerance and WUE in crop plants in a projected hotter and drier landscape in the 21st-century and beyond.

Bacillus subtilis STU6 Ameliorates Iron Deficiency in Tomato by Enhancement of Polyamine-Mediated Iron Remobilization

Iron (Fe) deficiency often triggers arginine overproduction in plants. However, it remains elusive whether Fe deficiency-induced increases of arginine levels are involved in beneficial rhizobacteria recruitment and that the mechanism underlying rhizobacteria induced plant Fe deficiency tolerance. Here, Bacillus subtilis STU6 increased soluble Fe content in tomato, thereby alleviating Fe deficiency-induced chlorosis. In a split-root system, STU6 significantly induced arginine exudation by Fe-deficient roots, and increased arginine levels promoted spermidine (Spd) production by STU6 and bacterial colonization. Deletion of the STU6 speB gene inhibited Spd synthesis and abrogated STU6-induced increments of soluble Fe content in the Fe-deficient plants. Increased host Spd levels by STU6 greatly stimulated the NO accumulation in the Fe-deficient roots. Furthermore, disruption of NO signaling markedly repressed STU6-mediated cell wall Fe remobilization. Collectively, our data provide important evidence that chemical dialogues between tomato and STU6 contribute to enhancement of microbe-mediated plant adaptation to Fe deficiency.

Plant Desiccation Tolerance and its Regulation in the Foliage of Resurrection “Flowering-Plant” Species

The majority of flowering-plant species can survive complete air-dryness in their seed and/or pollen. Relatively few species (‘resurrection plants’) express this desiccation tolerance in their foliage. Knowledge of the regulation of desiccation tolerance in resurrection plant foliage is reviewed. Elucidation of the regulatory mechanism in resurrection grasses may lead to identification of genes that can improve stress tolerance and yield of major crop species. Well-hydrated leaves of resurrection plants are desiccation-sensitive and the leaves become desiccation tolerant as they are drying. Such drought-induction of desiccation tolerance involves changes in gene-expression causing extensive changes in the complement of proteins and the transition to a highly-stable quiescent state lasting months to years. These changes in gene-expression are regulated by several interacting phytohormones, of which drought-induced abscisic acid (ABA) is particularly important in some species. Treatment with only ABA induces desiccation tolerance in vegetative tissue of Borya constricta Churchill. and Craterostigma plantagineum Hochstetter. but not in the resurrection grass Sporobolus stapfianus Gandoger. Suppression of drought-induced senescence is also important for survival of drying. Further research is needed on the triggering of the induction of desiccation tolerance, on the transition between phases of protein synthesis and on the role of the phytohormone, strigolactone and other potential xylem-messengers during drying and rehydration.

Quantitative Phosphoproteomic and Metabolomic Analyses Reveal GmMYB173 Optimizes Flavonoid Metabolism in Soybean under Salt Stress

Salinity causes osmotic stress to crops and limits their productivity. To understand the mechanism underlying soybean salt tolerance, proteomics approach was used to identify phosphoproteins altered by NaCl treatment. Results revealed that 412 of the 4698 quantitatively analyzed phosphopeptides were significantly up-regulated on salt treatment, including a phosphopeptide covering the serine 59 in the transcription factor GmMYB173. Our data showed that GmMYB173 is one of the three MYB proteins differentially phosphorylated on salt treatment, and a substrate of the casein kinase-II. MYB recognition sites exist in the promoter of flavonoid synthase gene GmCHS5 and one was found to mediate its recognition by GmMYB173, an event facilitated by phosphorylation. Because GmCHS5 catalyzes the synthesis of chalcone, flavonoids derived from chalcone were monitored using metabolomics approach. Results revealed that 24 flavonoids of 6745 metabolites were significantly up-regulated after salt treatment. We further compared the salt tolerance and flavonoid accumulation in soybean transgenic roots expressing the 35S promoter driven cds and RNAi constructs of GmMYB173 and GmCHS5, as well as phospho-mimic (GmMYB173S59D ) and phospho-ablative (GmMYB173S59A ) mutants of GmMYB173 Overexpression of GmMYB173S59D and GmCHS5 resulted in the highest increase in salt tolerance and accumulation of cyaniding-3-arabinoside chloride, a dihydroxy B-ring flavonoid. The dihydroxy B-ring flavonoids are more effective as anti-oxidative agents when compared with monohydroxy B-ring flavonoids, such as formononetin. Hence the salt-triggered phosphorylation of GmMYB173, subsequent increase in its affinity to GmCHS5 promoter and the elevated transcription of GmCHS5 likely contribute to soybean salt tolerance by enhancing the accumulation of dihydroxy B-ring flavonoids.

Overexpression of a tartary buckwheat R2R3-MYB transcription factor gene, FtMYB9, enhances tolerance to drought and salt stresses in transgenic Arabidopsis

Tartary buckwheat (Fagopyrum tataricum) is a traditional coarse cereal that exhibits strong plasticity in its adaptation to harsh and complicated environmental stresses. In an attempt to study the strong tolerance of tartary buckwheat, the FtMYB9 gene, which encodes an R2R3-MYB transcription factor protein, was functionally investigated. FtMYB9 expression was rapidly and strongly induced by ABA, cold, salt, and drought treatments in the seedling stage. A yeast one-hybrid system assay indicated that FtMYB9 is an activator of transcriptional activity, consistent with its roles as a transcription factor. Its overexpression in plants resulted in increased sensitivity to ABA at the germination and seedling stages compared to wild type. The overexpression of FtMYB9 increased tolerance to drought and salt stresses by the activation of some stress-related genes from both ABA-independent and ABA-dependent pathways in transgenic Arabidopsis. Furthermore, enhanced proline content and the activation of the P5CS1 gene implied that FtMYB9 may be involved in proline synthesis in plants. Collectively, these results suggest that FtMYB9 functions as a novel R2R3-MYB TF which plays positive roles in salt and drought tolerance by regulating different stress-responsive signaling pathways.

Whole-transcriptome sequence analysis of differentially expressed genes in Phormium tenax under drought stress

Phormium tenax is a kind of drought resistant garden plant with its rich and colorful leaves. To clarify the molecular mechanism of drought resistance in Phormium tenax, transcriptome was sequenced by the Illumina sequencing technology under normal and drought stress, respectively. A large number of contigs, transcripts and unigenes were obtained. Among them, only 30,814 unigenes were annotated by comparing with the protein databases. A total of 4,380 genes were differentially expressed, 2,698 of which were finally annotated under drought stress. Differentially expression analysis was also performed upon drought treatment. In KEGG pathway, the mechanism of drought resistance in Phormium tenax was explained from three aspects of metabolism and signaling of hormones, osmotic adjustment and reactive oxygen species metabolism. These results are helpful to understand the drought tolerance mechanism of Phormium tenax and will provide a precious genetic resource for drought-resistant vegetation breeding and research.

Functional Characterization of Cotton GaMYB62L, a Novel R2R3 TF in Transgenic Arabidopsis

Drought stress can trigger the production of ABA in plants, in response to adverse conditions, which induces the transcript of stress-related marker genes. The R2R3 MYB TFs are implicated in regulation of various plants developmental, metabolic and multiple environmental stress responses. Here, a R2R3-MYB cloned gene, GaMYB62L, was transformed in Arabidopsis and was functionally characterized. The GaMYB62L protein contains two SANT domains with a conserved R2R3 imperfect repeats. The GaMYB62L cDNA is 1,017 bp with a CDS of 879, encodes a 292-residue polypeptide with MW of 38.78 kD and a pI value of 8.91. Overexpressed GaMYB62L transgenic Arabidopsis have increased proline and chlorophyll content, superior seed germination rate under salt and osmotic stress, less water loss rate with reduced stomatal apertures, high drought avoidance as compared to WT on water deprivation and also significant plant survival rates at low temperature. In addition, overexpressed GaMYB62L lines were more sensitive to ABA mediated germination and root elongation assay. Moreover, ABA induced GaMYB62L overexpression, enhanced the expression of ABA stress related marker genes like RD22, COR15A, ADH1, and RD29A. Together, overexpression of GaMYB62L suggested having developed better drought, salt and cold tolerance in transgenic Arabidopsis and thus presented it as a prospective candidate gene to achieve better abiotic stress tolerance in cotton crop.

Transcriptomic Profiling Reveals Metabolic and Regulatory Pathways in the Desiccation Tolerance of Mungbean (Vigna radiata [L.] R. Wilczek)

Mungbean (Vigna radiate L. Wilczek) is an important legume crop for its valuable nutritional and health benefits. Desiccation tolerance (DT) is a capacity of seeds to survive and maintain physiological activities during storage and under stress conditions. Many studies of DT have been reported in other legume crop, such as soybean and Medicago truncatula with little studies in the mungbean. In this study, the transcript profiles of mungbean seeds under different imbibition times were investigated for DT using RNA-sequencing (RNA-seq). A total of 3210 differentially expressed genes (DEGs) were found at the key period of DT (3-18 h of imbibition). Gene ontology (GO) and KEGG analysis showed that the terms of "response to stimulus," "transcription regulator," "methylation," and "starch and sucrose metabolism" were enriched for DT. Clustering analysis also showed that many transcription factors (MYB, AP2, and NAC), HSPs, embryogenesis abundant (LEA) proteins, and genes encoding methyltransferase and histone were differentially expressed. Nine of these DEGs were further validated by quantitative RT-PCR (qRT-PCR). Our study extends our knowledge of mungbean transcriptomes and further provides insight into the molecular mechanism of DT as well as new strategies for developing drought-tolerant crops.

Plant MYB Transcription Factors: Their Role in Drought Response Mechanisms

Water scarcity is one of the major causes of poor plant performance and limited crop yields worldwide and it is the single most common cause of severe food shortage in developing countries. Several molecular networks involved in stress perception, signal transduction and stress responses in plants have been elucidated so far. Transcription factors are major players in water stress signaling. In recent years, different MYB transcription factors, mainly in Arabidopsis thaliana (L.) Heynh. but also in some crops, have been characterized for their involvement in drought response. For some of them there is evidence supporting a specific role in response to water stress, such as the regulation of stomatal movement, the control of suberin and cuticular waxes synthesis and the regulation of flower development. Moreover, some of these genes have also been characterized for their involvement in other abiotic or biotic stresses, an important feature considering that in nature, plants are often simultaneously subjected to multiple rather than single environmental perturbations. This review summarizes recent studies highlighting the role of the MYB family of transcription factors in the adaptive responses to drought stress. The practical application value of MYBs in crop improvement, such as stress tolerance engineering, is also discussed.

Identification of miR159s and their target genes and expression analysis under drought stress in potato

The MYB proteins comprise one of the largest families of plant transcription factors (TFs) and many of MYB families, which play essential roles in plant growth, development and respond to environmental stresses, and have yet been identified in plant. Previous research has shown that miR159 family members repressed the conserved plant R2R3 MYB domain TFs in model plants. In the present research, we identified three potato novel miR159 family members named as stu-miR159a, stu-miR159b and stu-miR159c based on bioinformatics analysis. Target prediction showed that they have a bite sit on the three GAMyb-like genes (StGAMyb-like1, StGAMyb-like2.1 and StGAMyb-like2.2) of potato. Those GAMyb-like genes also have been selected and cloned from potato, which belong to R2R3 MYB domain TFs. We further measured expressional levels of stu-miR159s and potato GAMyb-like genes during the different periods of drought treated samples using quantitative real-time PCR (qRT-PCR). The results showed that they had a opposite expression pattern, briefly, three stu-miR159 members showed similar expressional trends which were significantly decreased expression after experiencing 25 days of drought stress treatment, while the potato GAMyb-like family members were greatly increased. Therefore, we suggested that stu-miR159s negatively regulated the expression of potato GAMyb-like genes which responsible for drought stress. The findings can facilitate functional studies of miRNAs in plants and provide molecular evidence for involvement process of drought tolerance in potato.

Bioengineering for salinity tolerance in plants: state of the art

Genetic engineering of plants for abiotic stress tolerance is a challenging task because of its multifarious nature. Comprehensive studies for developing abiotic stress tolerance are in progress, involving genes from different pathways including osmolyte synthesis, ion homeostasis, antioxidative pathways, and regulatory genes. In the last decade, several attempts have been made to substantiate the role of "single-function" gene(s) as well as transcription factor(s) for abiotic stress tolerance. Since, the abiotic stress tolerance is multigenic in nature, therefore, the recent trend is shifting towards genetic transformation of multiple genes or transcription factors. A large number of crop plants are being engineered by abiotic stress tolerant genes and have shown the stress tolerance mostly at laboratory level. This review presents a mechanistic view of different pathways and emphasizes the function of different genes in conferring salt tolerance by genetic engineering approach. It also highlights the details of successes achieved in developing salt tolerance in plants thus far.

Asg1 is a stress-inducible gene which increases stomatal resistance in salt stressed potato

The identification of critical components in plant salt stress adaptation has greatly benefitted, in the last two decades, from fundamental discoveries in Arabidopsis and close model systems. Nevertheless, this approach has also highlighted a non-complete overlap between stress tolerance mechanisms in Arabidopsis and agricultural crops. Within a long-running research program aimed at identifying salt stress genetic determinants in potato by functional screening in Escherichia coli, we isolated Asg1, a stress-related gene with an unknown function. Asg1 is induced by salt stress in both potato and Arabidopsis and by abscisic acid in Arabidopsis. Asg1 is actively transcribed in all plant tissues. Furthermore, Asg1 promoter analysis confirmed its ubiquitous expression, which was remarkable in pollen, a plant tissue that undergoes drastic dehydration/hydration processes. Fusion of Asg1 with green fluorescent protein showed that the encoded protein is localized close to the plasma membrane with a non-continuous pattern of distribution. In addition, Arabidopsis knockout asg1 mutants were insensitive to both NaCl and sugar hyperosmotic environments during seed germination. Transgenic potato plants over-expressing the Asg1 gene revealed a stomatal hypersensitivity to NaCl stress which, however, did not result in a significantly improved tuber yield in stress conditions. Altogether, these data suggest that Asg1 might interfere with components of the stress signaling pathway by promoting stomatal closure and participating in stress adaptation.

Heterologous expression of the chrysanthemum R2R3-MYB transcription factor CmMYB2 enhances drought and salinity tolerance, increases hypersensitivity to ABA and delays flowering in Arabidopsis thaliana

Knowledge on genes related to plant responses to adverse growth conditions and development is essential for germplasm improvement. In this study, a chrysanthemum R2R3-MYB transcription factor gene, designated CmMYB2 (GenBank accession No. JF795918), was cloned and functionally characterized. Expression of CmMYB2 in chrysanthemum leaves was up-regulated in response to drought, salinity and cold stress, as well as by treatment with exogenous abscisic acid (ABA). When the gene was constitutively expressed in Arabidopsis thaliana, it increased plant sensitivity to ABA and reduced stomatal aperture. Plant survival under drought was improved than in the wild type, as was the plants' salinity tolerance. The level of expression of a number of genes associated with the stress response, including RD22, RD29A, RAB18, COR47, ABA1 and ABA2, was raised in the CmMYB2 transgenic Arabidopsis plants. CmMYB2 transgenic Arabidopsis plants were also delayed in flowering. The expression of CONSTANS (CO), FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), LEAFY (LFY) and APETALA1 (AP1) genes involved in flowering was down-regulated in the CmMYB2 transgenics. Together, these results suggest that CmMYB2 may be a promising gene for the drought and salt tolerance improvement and flowering-time modulation.

Molecular mechanisms of desiccation tolerance in resurrection plants

Resurrection plants are a small but diverse group of land plants characterized by their tolerance to extreme drought or desiccation. They have the unique ability to survive months to years without water, lose most of the free water in their vegetative tissues, fall into anabiosis, and, upon rewatering, quickly regain normal activity. Thus, they are fundamentally different from other drought-surviving plants such as succulents or ephemerals, which cope with drought by maintaining higher steady state water potential or via a short life cycle, respectively. This review describes the unique physiological and molecular adaptations of resurrection plants enabling them to withstand long periods of desiccation. The recent transcriptome analysis of Craterostigma plantagineum and Haberlea rhodopensis under drought, desiccation, and subsequent rehydration revealed common genetic pathways with other desiccation-tolerant species as well as unique genes that might contribute to the outstanding desiccation tolerance of the two resurrection species. While some of the molecular responses appear to be common for both drought stress and desiccation, resurrection plants also possess genes that are highly induced or repressed during desiccation with no apparent sequence homologies to genes of other species. Thus, resurrection plants are potential sources for gene discovery. Further proteome and metabolome analyses of the resurrection plants contributed to a better understanding of molecular mechanisms that are involved in surviving severe water loss. Understanding the cellular mechanisms of desiccation tolerance in this unique group of plants may enable future molecular improvement of drought tolerance in crop plants.

The overexpression of OsNAC9 alters the root architecture of rice plants enhancing drought resistance and grain yield under field conditions

Drought conditions limit agricultural production by preventing crops from reaching their genetically predetermined maximum yields. Here, we present the results of field evaluations of rice overexpressing OsNAC9, a member of the rice NAC domain family. Root-specific (RCc3) and constitutive (GOS2) promoters were used to overexpress OsNAC9 and produced the transgenic RCc3:OsNAC9 and GOS2:OsNAC9 plants. Field evaluations over two cultivating seasons showed that grain yields of the RCc3:OsNAC9 and the GOS2:OsNAC9 plants were increased by 13%-18% and 13%-32% under normal conditions, respectively. Under drought conditions, RCc3:OsNAC9 plants showed an increased grain yield of 28%-72%, whilst the GOS2:OsNAC9 plants remained unchanged. Both transgenic lines exhibited altered root architecture involving an enlarged stele and aerenchyma. The aerenchyma of RCc3:OsNAC9 roots was enlarged to a greater extent than those of GOS2:OsNAC9 and non-transgenic (NT) roots, suggesting the importance of this phenotype for enhanced drought resistance. Microarray experiments identified 40 up-regulated genes by more than threefold (P < 0.01) in the roots of both transgenic lines. These included 9-cis-epoxycarotenoid dioxygenase, an ABA biosynthesis gene, calcium-transporting ATPase, a component of the Ca(2+) signalling pathway involved in cortical cell death and aerenchyma formation, cinnamoyl CoA reductase 1, a gene involved in lignin biosynthesis, and wall-associated kinases¸ genes involved in cell elongation and morphogenesis. Interestingly, O-methyltransferase, a gene necessary for barrier formation, was specifically up-regulated only in the RCc3:OsNAC9 roots. Such up-regulated genes that are commonly and specifically up-regulated in OsNAC9 transgenic roots may account for the altered root architecture conferring increased drought resistance phenotype.

Molecular mechanisms of desiccation tolerance in resurrection plants

Resurrection plants are a small but diverse group of land plants characterized by their tolerance to extreme drought or desiccation. They have the unique ability to survive months to years without water, lose most of the free water in their vegetative tissues, fall into anabiosis, and, upon rewatering, quickly regain normal activity. Thus, they are fundamentally different from other drought-surviving plants such as succulents or ephemerals, which cope with drought by maintaining higher steady state water potential or via a short life cycle, respectively. This review describes the unique physiological and molecular adaptations of resurrection plants enabling them to withstand long periods of desiccation. The recent transcriptome analysis of Craterostigma plantagineum and Haberlea rhodopensis under drought, desiccation, and subsequent rehydration revealed common genetic pathways with other desiccation-tolerant species as well as unique genes that might contribute to the outstanding desiccation tolerance of the two resurrection species. While some of the molecular responses appear to be common for both drought stress and desiccation, resurrection plants also possess genes that are highly induced or repressed during desiccation with no apparent sequence homologies to genes of other species. Thus, resurrection plants are potential sources for gene discovery. Further proteome and metabolome analyses of the resurrection plants contributed to a better understanding of molecular mechanisms that are involved in surviving severe water loss. Understanding the cellular mechanisms of desiccation tolerance in this unique group of plants may enable future molecular improvement of drought tolerance in crop plants.

Multivariate analyses of salt stress and metabolite sensing in auto- and heterotroph Chenopodium cell suspensions

Global warming increases plant salt stress via evaporation after irrigation, but how plant cells sense salt stress remains unknown. Here, we searched for correlation-based targets of salt stress sensing in Chenopodium rubrum cell suspension cultures. We proposed a linkage between the sensing of salt stress and the sensing of distinct metabolites. Consequently, we analysed various extracellular pH signals in autotroph and heterotroph cell suspensions. Our search included signals after 52 treatments: salt and osmotic stress, ion channel inhibitors (amiloride, quinidine), salt-sensing modulators (proline), amino acids, carboxylic acids and regulators (salicylic acid, 2,4-dichlorphenoxyacetic acid). Multivariate analyses revealed hirarchical clusters of signals and five principal components of extracellular proton flux. The principal component correlated with salt stress was an antagonism of γ-aminobutyric and salicylic acid, confirming involvement of acid-sensing ion channels (ASICs) in salt stress sensing. Proline, short non-substituted mono-carboxylic acids (C2-C6), lactic acid and amiloride characterised the four uncorrelated principal components of proton flux. The proline-associated principal component included an antagonism of 2,4-dichlorphenoxyacetic acid and a set of amino acids (hydrophobic, polar, acidic, basic). The five principal components captured 100% of variance of extracellular proton flux. Thus, a bias-free, functional high-throughput screening was established to extract new clusters of response elements and potential signalling pathways, and to serve as a core for quantitative meta-analysis in plant biology. The eigenvectors reorient research, associating proline with development instead of salt stress, and the proof of existence of multiple components of proton flux can help to resolve controversy about the acid growth theory.

Role of transgenic plants in agriculture and biopharming

At present, environmental degradation and the consistently growing population are two main problems on the planet earth. Fulfilling the needs of this growing population is quite difficult from the limited arable land available on the globe. Although there are legal, social and political barriers to the utilization of biotechnology, advances in this field have substantially improved agriculture and human life to a great extent. One of the vital tools of biotechnology is genetic engineering (GE) which is used to modify plants, animals and microorganisms according to desired needs. In fact, genetic engineering facilitates the transfer of desired characteristics into other plants which is not possible through conventional plant breeding. A variety of crops have been engineered for enhanced resistance to a multitude of stresses such as herbicides, insecticides, viruses and a combination of biotic and abiotic stresses in different crops including rice, mustard, maize, potato, tomato, etc. Apart from the use of GE in agriculture, it is being extensively employed to modify the plants for enhanced production of vaccines, hormones, etc. Vaccines against certain diseases are certainly available in the market, but most of them are very costly. Developing countries cannot afford the disease control through such cost-intensive vaccines. Alternatively, efforts are being made to produce edible vaccines which are cheap and have many advantages over the commercialized vaccines. Transgenic plants generated for this purpose are capable of expressing recombinant proteins including viral and bacterial antigens and antibodies. Common food plants like banana, tomato, rice, carrot, etc. have been used to produce vaccines against certain diseases like hepatitis B, cholera, HIV, etc. Thus, the up- and down-regulation of desired genes which are used for the modification of plants have a marked role in the improvement of genetic crops. In this review, we have comprehensively discussed the role of genetic engineering in generating transgenic lines/cultivars of different crops with improved nutrient quality, biofuel production, enhanced production of vaccines and antibodies, increased resistance against insects, herbicides, diseases and abiotic stresses as well as the safety measures for their commercialization.

Achievements and challenges in understanding plant abiotic stress responses and tolerance

Intensive research over the last decade has gradually unraveled the mechanisms that underlie how plants react to environmental adversity. Genes involved in many of the essential steps of the stress response have been identified and characterized. In particular, the recent discovery of ABA receptors, progress in understanding the transcriptional and post-transcriptional regulation of stress-responsive gene expression, and studies on hormone interactions under stress have facilitated addressing the molecular basis of how plant cells respond to abiotic stress. Here, we summarize recent research progress on these issues, especially focusing on progress related to the essential and classically important signaling pathways and genes. Despite this wealth of achievements, many challenges remain not only for the further elucidation of stress response mechanisms but also for evaluation of the natural genetic variations and associating them with specific gene functions. Finally, the proper application of this knowledge to benefit humans and agriculture is another important issue that lies ahead. Collaborative wisdom and efforts are needed to confront these challenges.

Transcription factors as tools to engineer enhanced drought stress tolerance in plants

Plant growth and productivity are greatly affected by abiotic stresses such as drought, salinity, and temperature. Drought stress is one of the major limitations to crop productivity worldwide due to its multigene nature, making the production of transgenic crops a challenging prospect. To develop crop plant with enhanced tolerance of drought stress, a basic understanding of physiological, biochemical, and gene regulatory networks is essential. In the signal transduction network that leads from the perception of stress signals to the expression of stress-responsive genes, transcription factors (TFs) play an essential role. Because TFs, as opposed to most structural genes, tend to control multiple pathways steps, they have emerged as powerful tools for the manipulation of complex metabolic pathways in plants. One such class of TFs is DREB/CBF that binds to drought responsive cis-acting elements. Transgenic plants have been developed with enhanced stress tolerance by manipulating the expression of DREB/CBF. Recently the functions of an increasing number of plant TFs are being elucidated and increased understanding of these factors in controlling drought stress response has lead to practical approaches for engineering stress tolerance in plants. The utility of the various TFs in plant stress research we review is illustrated by several published examples. The manipulation of native plant regularity networks therefore represents a new era for genetically modified crops. This review focuses on the recent understanding, latest advancements related to TFs and present status of their deployment in developing stress tolerant transgenic plants.

Expression of StMYB1R-1, a novel potato single MYB-like domain transcription factor, increases drought tolerance

Potato (Solanum tuberosum) is relatively vulnerable to abiotic stress conditions such as drought, but the tolerance mechanisms for such stresses in potato are largely unknown. To identify stress-related factors in potato, we previously carried out a genetic screen of potato plants exposed to abiotic environmental stress conditions using reverse northern-blot analysis. A cDNA encoding a putative R1-type MYB-like transcription factor (StMYB1R-1) was identified as a putative stress-response gene. Here, the transcript levels of StMYB1R-1 were enhanced in response to several environmental stresses in addition to drought but were unaffected by biotic stresses. The results of intracellular targeting and quadruple 9-mer protein-binding microarray analysis indicated that StMYB1R-1 localizes to the nucleus and binds to the DNA sequence (G)/(A)GATAA. Overexpression of a StMYB1R-1 transgene in potato plants improved plant tolerance to drought stress while having no significant effects on other agricultural traits. Transgenic plants exhibited reduced rates of water loss and more rapid stomatal closing than wild-type plants under drought stress conditions. In addition, overexpression of StMYB1R-1 enhanced the expression of drought-regulated genes such as AtHB-7, RD28, ALDH22a1, and ERD1-like. Thus, the expression of StMYB1R-1 in potato enhanced drought tolerance via regulation of water loss. These results indicated that StMYB1R-1 functions as a transcription factor involved in the activation of drought-related genes.

Modulation of transcription factor and metabolic pathway genes in response to water-deficit stress in rice

Water-deficit stress is detrimental for rice growth, development, and yield. Transcriptome analysis of 1-week-old rice (Oryza sativa L. var. IR64) seedling under water-deficit stress condition using Affymetrix 57 K GeneChip® has revealed 1,563 and 1,746 genes to be up- and downregulated, respectively. In an effort to amalgamate data across laboratories, we identified 5,611 differentially expressing genes under varying extrinsic water-deficit stress conditions in six vegetative and one reproductive stage of development in rice. Transcription factors (TFs) involved in ABA-dependent and ABA-independent pathways have been found to be upregulated during water-deficit stress. Members of zinc-finger TFs namely, C₂H₂, C₂C₂, C₃H, LIM, PHD, WRKY, ZF-HD, and ZIM, along with TF families like GeBP, jumonji, MBF1 and ULT express differentially under water-deficit conditions. NAC (NAM, ATAF and CUC) TF family emerges to be a potential key regulator of multiple abiotic stresses. Among the 12 TF genes that are co-upregulated under water-deficit, salt and cold stress conditions, five belong to the NAC TF family. We identified water-deficit stress-responsive genes encoding key enzymes involved in biosynthesis of osmoprotectants like polyols and sugars; amino acid and quaternary ammonium compounds; cell wall loosening and structural components; cholesterol and very long chain fatty acid; cytokinin and secondary metabolites. Comparison of genes responsive to water-deficit stress conditions with genes preferentially expressed during panicle and seed development revealed a significant overlap of transcriptome alteration and pathways.

Dehydration tolerance in plants

Dehydration tolerance in plants is an important but understudied component of the complex phenotype of drought tolerance. Most plants have little capacity to tolerate dehydration; most die at leaf water potentials between -5 and -10 MPa. Some of the non-vascular plants and a small percentage (0.2%) of vascular plants, however, can survive dehydration to -100 MPa and beyond, and it is from studying such plants that we are starting to understand the components of dehydration tolerance in plants. In this chapter we define what dehydration tolerance is and how it can be assessed, important prerequisites to understanding the response of a plant to water loss. The metabolic and mechanical consequences of cellular dehydration in plants prelude a discussion on the role that gene expression responses play in tolerance mechanisms. We finally discuss the key biochemical aspects of tolerance focusing on the roles of carbohydrates, late embryogenesis abundant and heat shock proteins, reactive oxygen scavenging (ROS) pathways, and novel transcription factors. It is clear that we are making significant advances in our understanding of dehydration tolerance and the added stimulus of new model systems will speed our abilities to impact the search for new strategies to improve drought tolerance in major crops.

Engineering the future. Development of transgenic plants with enhanced tolerance to adverse environments

Environmental stresses - especially drought and salinity - and iron limitation are the primary causes of crop yield losses. Therefore, improvement of plant stress tolerance has paramount relevance for agriculture, and vigorous efforts are underway to design stress-tolerant crops. Three aspects of this ongoing research are reviewed here. First, attempts have been made to strengthen endogenous plant defences, which are characterised by intertwined, hierarchical gene networks involved in stress perception, signalling, regulation and expression of effector proteins, enzymes and metabolites. The multigenic nature of this response requires detailed knowledge of the many actors and interactions involved in order to identify proper intervention points, followed by significant engineering of the prospective genes to prevent undesired side-effects. A second important aspect refers to the effect of concurrent stresses as plants normally meet in the field (e.g., heat and drought). Recent findings indicate that plant responses to combined environmental hardships are somehow unique and cannot be predicted from the addition of the individual stresses, underscoring the importance of programming research within this conceptual framework. Finally, the photosynthetic microorganisms from which plants evolved (i.e., algae and cyanobacteria) deploy a totally different strategy to acquire stress tolerance, based on the substitution of stress-vulnerable targets by resistant isofunctional proteins that could take over the lost functions under adverse conditions. Reintroduction of these ancient traits in model and crop plants has resulted in increased tolerance to environmental hardships and iron starvation, opening a new field of opportunities to increase the endurance of crops growing under suboptimal conditions.

Transgenic expression of MYB15 confers enhanced sensitivity to abscisic acid and improved drought tolerance in Arabidopsis thaliana

Abiotic stresses cause serious crop losses. Knowledge on genes functioning in plant responses to adverse growth conditions is essential for developing stress tolerant crops. Here we report that transgenic expression of MYB15, encoding a R2R3 MYB transcription factor in Arabidopsis thaliana, conferred hypersensitivity to exogenous abscisic acid (ABA) and improved tolerance to drought and salt stresses. The promoter of MYB15 was active in not only vegetative and reproductive organs but also the guard cells of stomata. Its transcript level was substantially upregulated by ABA, drought or salt treatments. Compared with wild type (WT) control, MYB15 overexpression lines were hypersensitive to ABA in germination assays, more susceptible to ABA-elicited inhibition of root elongation, and more sensitive to ABA-induced stomatal closure. In line with the above findings, the transcript levels of ABA biosynthesis (ABA1, ABA2), signaling (ABI3), and responsive genes (AtADH1, RD22, RD29B, AtEM6) were generally higher in MYB15 overexpression seedlings than in WT controls after treatment with ABA. MYB15 overexpression lines displayed improved survival and reduced water loss rates than WT control under water deficiency conditions. These overexpression lines also displayed higher tolerance to NaCl stress. Collectively, our data suggest that overexpression of MYB15 improves drought and salt tolerance in Arabidopsis possibly by enhancing the expression levels of the genes involved in ABA biosynthesis and signaling, and those encoding the stress-protective proteins.

Crosstalk between biotic and abiotic stress responses in tomato is mediated by the AIM1 transcription factor

Plants deploy diverse molecular and cellular mechanisms to survive in stressful environments. The tomato (Solanum lycopersicum) abscisic acid-induced myb1 (SlAIM1) gene encoding an R2R3MYB transcription factor is induced by pathogens, plant hormones, salinity and oxidative stress, suggesting a function in pathogen and abiotic stress responses. Tomato SlAIM1 RNA interference (RNAi) plants with reduced SlAIM1 gene expression show an increased susceptibility to the necrotrophic fungus Botrytis cinerea, and increased sensitivity to salt and oxidative stress. Ectopic expression of SlAIM1 is sufficient for tolerance to high salinity and oxidative stress. These responses correlate with reduced sensitivity to abscisic acid (ABA) in the SlAIM1 RNAi, but increased sensitivity in the overexpression plants, suggesting SlAIM1-mediated ABA responses are required to integrate tomato responses to biotic and abiotic stresses. Interestingly, when exposed to high root-zone salinity levels, SlAIM1 RNAi plants accumulate more Na(+), whereas the overexpression lines accumulate less Na(+) relative to wild-type plants, suggesting that SlAIM1 regulates ion fluxes. Transmembrane ion flux is a hallmark of early responses to abiotic stress and pathogen infection preceding hypersensitive cell death and necrosis. Misregulation of ion fluxes can result in impaired plant tolerance to necrotrophic infection or abiotic stress. Our data reveal a previously uncharacterized connection between ABA, Na(+) homeostasis, oxidative stress and pathogen response, and shed light on the genetic control of crosstalk between plant responses to pathogens and abiotic stress. Together, our data suggest SlAIM1 integrates plant responses to pathogens and abiotic stresses by modulating responses to ABA.

Tolerance to various environmental stresses conferred by the salt-responsive rice gene ONAC063 in transgenic Arabidopsis

Environmental stresses limit plant growth and crop production worldwide. We attempted to isolate rice genes involved in conferring tolerance to environmental stresses by using a transgenic Arabidopsis population expressing full-length cDNAs of rice. Among these lines, a thermotolerant line, R08946, was detected. The rice cDNA inserted in R08946 encoded a NAC transcription factor, ONAC063. This protein was localized in the nucleus and showed transactivation activity at the C-terminus. ONAC063 expression was not induced by high-temperature but highly induced by high-salinity in rice roots. High-osmotic pressure and reactive oxygen species levels also induced ONAC063 expression. The seeds of ONAC063-expressing transgenic Arabidopsis showed enhanced tolerance to high-salinity and osmotic pressure. Microarray and real-time reverse transcription-polymerase chain reaction analyses showed upregulated expression of some salinity-inducible genes, including the amylase gene AMY1, in ONAC063-expressing transgenic Arabidopsis. Thus, ONAC063 may play an important role in eliciting responses to high-salinity stress.

Isolation and functional characterization of the Arabidopsis salt-tolerance 32 (AtSAT32) gene associated with salt tolerance and ABA signaling

Recently, we have isolated salt-tolerance genes (SATs) on the basis of the overexpression screening of yeast with a maize cDNA library from kernels. One of the selected genes [salt-tolerance 32 (SAT32)] appears to be a key determinant for salt stress tolerance in yeast cells. Maize SAT32 cDNA encodes for a 49-kDa protein, which is 41% identity with the Arabidopsis salt-tolerance 32 (AtSAT32) unknown gene. Arabidopsis Transfer-DNA (T-DNA) knockout AtSAT32 (atsat32) altered root elongation, including reduced silique length and reduced seed number. In an effort to further assess salinity tolerance in Arabidopsis, we have functionally characterized the AtSAT32 gene and determined that salinity and the plant hormone ABA induced the expression of AtSAT32. The atsat32 mutant was more sensitive to salinity than the wild-type plant. On the contrary, Arabidopsis overexpressing AtSAT32 (35S::AtSAT32) showed enhanced salt tolerance and increased activity of vacuolar H(+)-pyrophosphatase (V-PPase, EC 3.6.1.1) under high-salt conditions. Consistent with these observations, 35S::AtSAT32 plants exhibited increased expression of salt-responsive and ABA-responsive genes, including the Rd29A, Erd15, Rd29B, Rd22 and RAB18 genes. Therefore, our results indicate that AtSAT32 is involved in both salinity tolerance and ABA signaling as a positive regulator in Arabidopsis.

Towards a systems-based understanding of plant desiccation tolerance

Vegetative desiccation tolerance occurs in a unique group of species termed 'resurrection plants'. Here, we review the molecular genetic, physiological, biochemical, ultrastructural and biophysical studies that have been performed on a variety of resurrection plants to discover the mechanisms responsible for their tolerance. Desiccation tolerance in resurrection plants involves a combination of molecular genetic mechanisms, metabolic and antioxidant systems as well as macromolecular and structural stabilizing processes. We propose that a systems-biology approach coupled with multivariate data analysis is best suited to unraveling the mechanisms responsible for plant desiccation tolerance, as well as their integration with one another. This is of particular relevance to molecular biological engineering strategies for improving plant drought tolerance in important crop species, such as maize (Zea mays) and grapevine (Vitis vinifera).

Real-time PCR monitoring of signal transduction related genes involved in water stress tolerance mechanism of sunflower

The study deals with the quantitative expression pattern of genes involved in signaling transduction pathways in response to water stress in leaves and embryos of a water stress tolerant genotype compared to a non-tolerant genotype using real-time quantitative PCR. The experiment was conducted in the field. The results showed a high quantitative up-regulation of genes belonging to protein kinase, phosphatase and transcription factor pathways (from two to 70 fold) only in leaves of the tolerant genotype compared to the non-tolerant genotype. Moreover, genes related to the protein kinase pathway were down-regulated in leaves of the non-tolerant genotype. On the contrary, in seeds, our study showed that the positive regulation of genes related to the signal transduction pathway observed in leaves of the tolerant genotype is turned off, suggesting different transcriptional control of signaling water stress in reproductive organs compared to vegetative organs.

Soybean GmMYB76, GmMYB92, and GmMYB177 genes confer stress tolerance in transgenic Arabidopsis plants

MYB-type transcription factors contain the conserved MYB DNA-binding domain of approximately 50 amino acids and are involved in the regulation of many aspects of plant growth, development, metabolism and stress responses. From soybean plants, we identified 156 GmMYB genes using our previously obtained 206 MYB unigenes, and 48 were found to have full-length open-reading frames. Expressions of all these identified genes were examined, and we found that expressions of 43 genes were changed upon treatment with ABA, salt, drought and/or cold stress. Three GmMYB genes, GmMYB76, GmMYB92 and GmMYB177, were chosen for further analysis. Using the yeast assay system, GmMYB76 and GmMYB92 were found to have transactivation activity and can form homodimers. GmMYB177 did not appear to have transactivation activity but can form heterodimers with GmMYB76. Yeast one-hybrid assay revealed that all the three GmMYBs could bind to cis-elements TAT AAC GGT TTT TT and CCG GAA AAA AGG AT, but with different affinity, and GmMYB92 could also bind to TCT CAC CTA CC. The transgenic Arabidopsis plants overexpressing GmMYB76 or GmMYB177 showed better performance than the GmMYB92-transgenic plants in salt and freezing tolerance. However, these transgenic plants exhibited reduced sensitivity to ABA treatment at germination stage in comparison with the wild-type plants. The three GmMYB genes differentially affected a subset of stress-responsive genes in addition to their regulation of a common subset of stress-responsive genes. These results indicate that the three GmMYB genes may play differential roles in stress tolerance, possibly through regulation of stress-responsive genes.

Raising salinity tolerant rice: recent progress and future perspectives

With the rapid growth in population consuming rice as staple food and the deteriorating soil and water quality around the globe, there is an urgent need to understand the response of this important crop towards these environmental abuses. With the ultimate goal to raise rice plant with better suitability towards rapidly changing environmental inputs, intensive efforts are on worldwide employing physiological, biochemical and molecular tools to perform this task. In this regard, efforts of plant breeders need to be duly acknowledged as several salinity tolerant varieties have reached the farmers field. Parallel efforts from molecular biologists have yielded relevant knowledge related to perturbations in gene expression and proteins during stress. Employing transgenic technology, functional validation of various target genes involved in diverse processes such as signaling, transcription, ion homeostasis, antioxidant defense etc for enhanced salinity stress tolerance has been attempted in various model systems and some of them have been extended to crop plant rice too. However, the fact remains that these transgenic plants showing improved performance towards salinity stress are yet to move from 'lab to the land'. Pondering this, we propose that future efforts should be channelized more towards multigene engineering that may enable the taming of this multigene controlled trait. Recent technological achievements such as the whole genome sequencing of rice is leading to a shift from single gene based studies to genome wide analysis that may prove to be a boon in re-defining salt stress responsive targets.

Changes of some anti-oxidative physiological indices under soil water deficits among 10 wheat (Triticum aestivum L.) genotypes at tillering stage

Drought is one of the major ecological factors limiting crop production and food quality globally, especially in the arid and semi-arid areas of the world. Wheat is the staple food for more than 35% of world population and wheat cultivation is mainly restricted to such zones with scarcity of water, so wheat anti-drought physiology study is of importance to wheat production, food safety and quality and biotechnological breeding for the sake of coping with abiotic and biotic conditions. The current study is to investigate changes of anti-oxidative physiological indices of 10 wheat genotypes at tillering stage. The main results and conclusion of tillering stage in terms of activities of POD, SOD, CAT and MDA content as followed: (1) 10 wheat genotypes can be generally grouped into three kinds (A-C, respectively) according to their changing trend of the measured indices; (2) A group performed better drought resistance under the condition of treatment level 1 (appropriate level), whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher and MDA lower; (3) B group exhibited stronger anti-drought under treatment level 2 (light-stress level), whose activities of anti-oxidative enzymes were higher and MDA lower; (4) C group expressed anti-drought to some extent under treatment level 3 (serious-stress), whose activities of anti-oxidative enzymes were stronger, MDA lower; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom). The study in this respect is the key to wheat anti-drought and biological-saving water in worldwide arid and semi-arid areas; (6) POD, SOD, and CAT activities and MDA content of different wheat genotypes had quite different changing trend at different stages and under different soil water stress conditions, which was linked with their origin of cultivation and individual soil water threshold, which will provide better reference to selecting proper plant species for eco-environmental construction and crops for sustainable agriculture in arid and semi-arid areas.

Abiotic and biotic stress tolerance in Arabidopsis overexpressing the multiprotein bridging factor 1a (MBF1a) transcriptional coactivator gene

We conducted a genetic yeast screen to identify salt tolerance (SAT) genes in a maize kernel cDNA library. During the screening, we identified a maize clone (SAT41) that seemed to confer elevated salt tolerance in comparison to control cells. SAT41 cDNA encodes a 16-kDa protein which is 82.4% identical to the Arabidopsis Multiprotein bridging factor 1a (MBF1a) transcriptional coactivator gene. To further examine salinity tolerance in Arabidopsis, we functionally characterized the MBF1a gene and found that dehydration as well as heightened glucose (Glc) induced MBF1a expression. Constitutive expression of MBF1a in Arabidopsis led to elevated salt tolerance in transgenic lines. Interestingly, plants overexpressing MBF1a exhibited insensitivity to Glc and resistance to fungal disease. Our results suggest that MBF1a is involved in stress tolerance as well as in ethylene and Glc signaling in Arabidopsis.

Relationship between water use efficiency (WUE) and production of different wheat genotypes at soil water deficit

Through 2-year field experiments, 7 wheat genotypes were better in their field yield. These 7 wheat genotypes and other 3 wheat species, which are being popularized on a large scale in different locations of China, were selected as experimental materials for the sake of measuring their difference in WUE and production and comparing their relationship at soil water deficits, future more, providing better drought resistance lines and theoretical guide for wheat production and practices and exploring anti-drought physiological mechanisms of different wheat genotypes. Under the condition of 3 soil-water-stress treatments (75% field capacity (FC), 55% FC, 45% FC, named level 1, level 2 and level 3, respectively), pot experiments for them were conducted and the related data were collected from their life circle. The main results were as followed: (1) according to the selected soil stress levels, water use efficiency (WUE) of 10 different wheat genotypes was divided into two groups (A and B); group A included genotypes 2, 3, 4, 5, 6, 7, 8, whose WUE decreased basically from level 1 to level 3 and reached individual peak of WUE at level 1; Group 2 included genotypes 1, 9, 10, whose WUE reached their individual peak at level 2; (2) based on total water consumption through all life circle, genotypes 1, 4, 8, 9 had lower water consumption (TWC) at level 1, genotypes 2, 3, 5, 6, 7 lower TWC at level 2, genotype 10 lower TWC at level 3; (3) at level 1, genotypes 2, 3, 4, 5, 6, 7, 8 had higher grain weight of single spike (GWSS), genotypes 1, 9, 10 better GWSS at level 2, which was in good line with individual WUE of different wheat genotypes; (4) by analyzing the indexes related to examining cultivars, it was found that genotypes 1, 2, 3, 4, 5, 6, 9, 10 had longer plant length (PL), spike length (SL), bigger grain number (GN) except genotypes 7 and 8 at level 1, RL was in better line with genotypes 1, 2, 3, 8, 9, 10, but not in the other genotypes at level 1.

A novel ABA-hypersensitive mutant in Arabidopsis defines a genetic locus that confers tolerance to xerothermic stress

Hot and dry air (harmattan or xerothermic climate) greatly inhibits plant growth, particularly flowering and seed setting of crops. Little is known about the mechanism of plant response to this extreme environmental stress due to the lack of valuable genetic resource. Here, we report the isolation and characteristics of a unique Arabidopsis mutant, hat1 (harmattan tolerant 1), which shows high tolerance to hot and dry air. Under normal growth conditions, the mutant does not differ in morphology and soil drought tolerance compared to the wild type. When subjected to high temperature (42 degrees C) and low humidity (10-15%), however, it could survive up to 6 days, while the wild type (Col-0) died after 24 h. The hat1 mutant also exhibits enhanced tolerance to soil drought, but only under xerothermic conditions. Mutant plants tightly close their stomata to retain water under xerothermic stress, and are more tolerant to high salinity at all developmental stages, accumulating less Na+ and more K+ than wild-type plants during NaCl treatment. Interestingly, hat1 plants are also ABA-hypersensitive. Genetic analysis revealed that the hat1 phenotype is caused by a dominant mutation at a single nuclear locus. Mapping studies indicate that Hat1 is located at an interval of 168 kb on chromosome 5 in which 21 genes are known to be regulated by diverse abiotic stresses. A mutant of this kind, to our knowledge, has not been previously reported. Thus, this report serves as a starting point in the genetic dissection of the plant response to xerothermic stress, and provides physiological and genetic evidence of the existence of a novel abiotic stress response pathway that is also ABA-dependent.

Transcriptome profiling uncovers metabolic and regulatory processes occurring during the transition from desiccation-sensitive to desiccation-tolerant stages in Medicago truncatula seeds

To investigate regulatory processes and protective mechanisms leading to desiccation tolerance (DT) in seeds, 16086-element microarrays were used to monitor changes in the transcriptome of desiccation-sensitive 3-mm-long radicles of Medicago truncatula seeds at different time points during incubation in a polyethylene glycol (PEG) solution at -1.7 MPa, resulting in a gradual re-establishment of DT. Gene profiling was also performed on embryos before and after the acquisition of DT during maturation. More than 1300 genes were differentially expressed during the PEG incubation. A large number of genes involved in C metabolism are expressed during the re-establishment of DT. Quantification of C reserves confirms that lipids, starch and oligosaccharides were mobilised, coinciding with the production of sucrose during the early osmotic adjustment. Several clusters of gene profiles were identified with different time-scales. Genes expressed early during the PEG incubation belonged to classes involved in early stress and adaptation responses. Interestingly, several regulatory genes typically expressed during abiotic/drought stresses were also upregulated during maturation, arguing for the partial overlap of ABA-dependent and -independent regulatory pathways involved in both drought and DT. At later time points, in parallel to the re-establishment of DT, upregulated genes are comparable with those involved in late seed maturation. Concomitantly, a massive repression of genes belonging to numerous classes occurred, including cell cycle, biogenesis, primary and energy metabolism. The re-establishment of DT in the germinated radicles appears to concur with a partial return to the quiescent state prior to germination.

Effect of water deficits on the activity of anti-oxidative enzymes and osmoregulation among three different genotypes of Radix Astragali at seeding stage

Water is a key factor influencing the yield and quality of crops. Plants mainly adapt to water deficits by biochemical changes and osmotic adjustment (OA). Research on drought tolerance of field crops has been done intensively, but there is little work to be done in medical plants. Traditional Chinese medicine (TCM) has a long history of several thousand years. TCM is playing an important role in daily life in China and applied widely in clinical experience on the globe. More and more wild medical plants are cultivated and introduced. It is known that ecological and environmental conditions are vital to cultivation and efficient component accumulation of medical plants. This study is concerned about biochemical changes of three genotypes of Radix Astragali during water deficient periods and we evaluated the relative ability of their drought tolerance on the above basis. We analyzed the effect of soil water deficits on antioxidant enzymes activity and osmoregulation substances in R. Astragali leaves of three genotypes collected on day 0, 5, 10, 15, 20 and 25 after onset of water deprivation. Under water deficient conditions, biochemical changes include protecting enzyme system, for instance superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Osmoregulation matters include proline (Pro) and soluble sugar. Antioxidant enzyme activities and Pro, and soluble sugar content correlated between water deficient degree and time course. Antioxidant enzyme activities increased before 20 days, then decreased at the end of experiment. Proline content increased gradually, and soluble sugar content reached the highest on day 20. The order of the ability of drought tolerance in three genotypes of R. Astragali is Mongolia>Wild>Hebei by using index of drought tolerance. The research results are instructive for cultivation and introduction of R. Astragali under different conditions of water status.

Osmotic regulation of 10 wheat (Triticum aestivum L.) genotypes at soil water deficits

Drought is a worldwide problem, seriously influencing plant (crop) productivity. Wheat is a stable food for 35% of the world population, moreover about 60% of land area on the globe belongs to arid and semi-arid zone. Wheat drought resistance is a multi-gene-controlling quantitative character and wheat final production in field is realized mainly by physiological regulation under the condition of multi-environmental factor interaction. Exploring drought resistance physiological mechanisms for different wheat genotypes is of importance to finding new drought resistance gene resources and conventional breeding and the basis for wheat drought resistance biotechnological breeding and platform. Osmotic adjustment regulation is the main component for physiological machinery of wheat drought resistance. By pot-cultivating experiments, investigation of osmotic adjustment comparison for 10 wheat genotypes at soil water deficits (75% FC, 55% FC, 45% FC, respectively), was conducted. The main results were as followed: (1) K(+) content in 10 wheat genotypes at three levels of soil water stress and at the same soil water deficit was very different. Five of these 10 wheat genotypes had higher K K(+) content under the condition of 75% FC. (2) Five of these 10 wheat genotypes possessed greater soluble sugar content at 55% FC soil water level. (3) Proline (Pro) content in five wheat genotypes was higher at 75% FC. (4) Five of these 10 wheat genotypes had lower malondialdehyde (MDA) content at 45% FC at seedling stage. Osmotic adjustment of wheat different genotypes was discussed in terms of different content of osmotic solutes.

Changes of anti-oxidative enzymes and MDA content under soil water deficits among 10 wheat (Triticum aestivum L.) genotypes at maturation stage

Drought is a world-spread problem seriously influencing grain production and quality, the loss of which is the total for other natural disasters, with increasing global climate change making the situation more serious. Wheat is the staple food for more than 35% of world population, so wheat anti-drought physiology study is of importance to wheat production and biological breeding for the sake of coping with abiotic and biotic conditions. Much research is involved in this hot topic, but the pace of progress is not so large because of drought resistance being a multiple-gene-control quantitative character and wheat genome being larger (16,000Mb). On the other hand, stress adaptive mechanisms are quite different, with stress degree, time course, materials, soil quality status and experimental plots, thus increasing the complexity of the issue in question. Additionally, a little study is related to the whole life circle of wheat, which cannot provide a comprehensive understanding of its anti-drought machinery. We selected 10 kinds of wheat genotypes as materials, which have potential to be applied in practice, and measured change of relative physiological indices through wheat whole growing-developmental circle (i.e. seedling, tillering and maturing). Here, we reported the anti-oxidative results of maturation stage (the results of seedling and tillering stage have been published) in terms of activities of POD, SOD, CAT and MDA content as follows: (1) 10 wheat genotypes can be grouped into three kinds (A-C, respectively) according to their changing trend of the measured indices; (2) A group performed better resistance drought under the condition of treatment level 1 (appropriate level), whose activities of anti-oxidative enzymes (POD, SOD, CAT) were higher and MDA lower; (3) B group exhibited stronger anti-drought under treatment level 2 (light-stress level), whose activities of anti-oxidative enzymes were higher and MDA lower; (4) C group expressed anti-drought to some extent under treatment level 3 (serious-stress level), whose activities of anti-oxidative enzymes were stronger, MDA lower; (5) these results demonstrated that different wheat genotypes have different physiological mechanisms to adapt themselves to changing drought stress, whose molecular basis is discrete gene expression profiling (transcriptom); (6) our results also showed that the concept and method accepted and adopted by most researchers [T.C. Hsiao, Plant response to water stress, Ann. Rev. Plant Physiol. 24 (1973) 519-570], that 75% FC is a proper supply for higher plants, was doubted, because this level could not reflect the true suitable level of different wheat genotypes. The study in this respect is the key to wheat anti-drought and biological-saving water agriculture; (7) our research can provide insights into physiological mechanisms of crop anti-drought and direct practical materials for wheat anti-drought breeding; (8) the physiological study of wheat is more urgent up-to-date and molecular aspects are needed, but cannot substitute this important part. The combination of both is an important strategy and a key and (9) POD, SOD and CAT activities and MDA content of different wheat genotypes had quite different changing trend at different stages and under different soil water stress conditions, which was linked with their origin of cultivation and individual soil water threshold.

A Lily ASR protein involves abscisic acid signaling and confers drought and salt resistance in Arabidopsis

LLA23, an abscisic acid-, stress-, and ripening-induced protein, was previously isolated from lily (Lilium longiflorum) pollen. The expression of LLA23 is induced under the application of abscisic acid (ABA), NaCl, or dehydration. To provide evidence on the biological role of LLA23 proteins against drought, we used an overexpression approach in Arabidopsis (Arabidopsis thaliana). Constitutive overexpression of LLA23 under the cauliflower mosaic virus 35S promoter confers reduced sensitivity to ABA in Arabidopsis seeds and, consequently, a reduced degree of seed dormancy. Transgenic 35SLLA23 seeds are able to germinate under unfavorable conditions, such as inhibitory concentrations of mannitol and NaCl. At the molecular level, altered expression of ABA/stress-regulated genes was observed. Thus, our results provide strong in vivo evidence that LLA23 mediates stress-responsive ABA signaling. In vegetative tissues, it is intriguing that Arabidopsis 35SLLA23 stomata remain opened upon drought, while transgenic plants have a decreased rate of water loss and exhibit enhanced drought and salt resistance. A dual function of the lily abscisic acid-, stress-, and ripening-induced protein molecule is discussed.