Carbohydrate metabolism and cell protection mechanisms differentiate drought tolerance and sensitivity in advanced potato clones (Solanum tuberosum L.)

Drought priming induced thermotolerance in wheat (Triticum aestivum L.) during reproductive stage; a multifaceted tolerance approach against terminal heat stress

In wheat (Triticum aestivum L.), terminal heat stress obstructs reproductive functioning eventually leading to yield loss. Drought priming during the vegetative stage can trigger a quicker and effective defense response against impending high temperature stress and improve crop production. In the present study, two contrasting wheat cultivars (PBW670 and C306) were subjected to moderate drought stress of 50-55% field capacity for eight days during the jointing stage to generate drought priming (DP) response. Fifteen days after anthesis heat stress (36 °C) was imposed for three days and physiological response of primed, and non-primed plants was assessed by analyzing membrane damage, water status and antioxidative enzymes. Heat shock transcription factors (14 TaHSFs), calmodulin (TaCaM5), antioxidative genes (TaSOD, TaPOX), polyamine biosynthesis genes and glutathione biosynthesis genes were analyzed. GC-MS based untargeted metabolite profiling was carried out to underpin the associated metabolic changes. Yield related parameters were recorded at maturity to finally assess the priming response. Heat stress response was visible from day one of exposure in terms of membrane damage and elevated antioxidative enzymes activity. DP reduced the impact of heat stress by lowering the membrane damage (ELI, MDA & LOX) and enhancing antioxidative enzyme activity except APX in both the cultivars. Drought priming upregulated the expression of HSFs, calmodulin, antioxidative genes, polyamines, and the glutathione biosynthesis genes. Drought priming altered key amino acids, carbohydrate, and fatty acid metabolism in PBW670 but also promoted thermotolerance in C306. Overall, DP provided a multifaceted approach against heat stress and positive association with yield.

Physio-morphological traits and osmoregulation strategies of hybrid maize (Zea mays) at the seedling stage in response to water-deficit stress

Drought has been identified as a major factor restricting maize productivity worldwide, especially in the rainfed areas. The objective of the present study was to investigate the physiological adaptation strategies and sugar-related gene expression levels in three maize (Zea mays L.) genotypes with different drought tolerance abilities (Suwan4452, drought tolerant as a positive check; S7328, drought susceptible as a negative check; Pac339, drought susceptible) at the seedling stage. Ten-day old seedlings of maize genotypes were subjected to (i) well-watered (WW) or control and (ii) water-deficit (WD) conditions. Leaf osmotic potential of cv. S7328 under WD was significantly decreased by 1.35-1.45 folds compared with cv. Pac339 under WW, whereas it was retained in cv. Suwan4452, which utilized total soluble sugars as the major osmolytes for maintaining leaf greenness, F_v/F_m, Φ_PSII, and stomatal function (P_n, net photosynthetic rate; g_s, stomatal conductance; and E, transpiration rate). Interestingly, sucrose degradation (65% over the control) in cv. Pac339 under WD was evident in relation to the downregulation of the ZmSPS1 level, whereas glucose enrichment (1.65 folds over the control) was observed in relation to the upregulation of ZmSPS1 and ZmSUS1. Moreover, CWSI (crop water stress index), calculated from leaf temperature of stressed plants, was negatively correlated with E, g_s, and P_n. Overall, growth characteristics, aboveground and belowground parts, in the drought-susceptible cv. Pac339 and cv. S7328, were significantly decreased (> 25% over the control), whereas these parameters in the drought-tolerant cv. Suwan4452 were unaffected. The study validates the use of leaf temperature, CWSI, P_n, g_s, and E as sensitive parameters and overall growth characters as effective indices for drought tolerance screening in maize genotypes at the seedling stage. However, further experiments are required to validate the results observed in this study under field conditions.

Acetic acid improves drought acclimation in soybean: an integrative response of photosynthesis, osmoregulation, mineral uptake and antioxidant defense

Exposure to drought stress negatively affects plant productivity and consequently threatens global food security. As global climates change, identifying solutions to increase the resilience of plants to drought is increasingly important. Several chemical treatments have recently emerged as promising techniques for various individual and combined abiotic stresses. This study shows compelling evidence on how acetic acid application promotes drought acclimation responses in soybean by investigating several morphological, physiological and biochemical attributes. Foliar applications of acetic acid to drought-exposed soybean resulted in improvements in root biomass, leaf area, photosynthetic rate and water use efficiency; leading to improved growth performance. Drought-induced accumulation of reactive oxygen species, and the resultant increased levels of malondialdehyde and electrolyte leakage, were considerably reverted by acetic acid treatment. Acetic acid-sprayed plants suffered less oxidative stress due to the enhancement of antioxidant defense mechanisms, as evidenced by the increased activities of superoxide dismutase, ascorbate peroxidase, catalase, glutathione peroxidase and glutathione S-transferase. Improved shoot relative water content was also linked to the increased levels of soluble sugars and free amino acids, indicating a better osmotic adjustment following acetic acid treatment in drought-exposed plants. Acetic acid also increased stem/root, leaf/stem and leaf/root mineral ratios and improved overall mineral status in drought-stressed plants. Taken together, our results demonstrated that acetic acid treatment enabled soybean plants to positively regulate photosynthetic ability, water balance, mineral homeostasis and antioxidant responses; thereby suggesting acetic acid as a cost-effective and easily accessible chemical for the management of soybean growth and productivity in drought-prone areas.

Overexpression of Os-microRNA408 enhances drought tolerance in perennial ryegrass

As a conserved microRNA (miRNA) family in plants, miR408 is known to be involved in different abiotic stress responses, including drought. Interestingly, some studies indicated a species- and/or cultivar-specific drought-responsive characteristic of miR408 in plant drought stress. Moreover, the functions of miR408 in perennial grass species are unknown. In this study, we investigated the role of miR408 in perennial ryegrass (Lolium perenne L.) by withholding water for 10 days for both wild type and transgenic plants with heterologous expression of rice (Oryza sativa L.) miR408 gene, Os-miR408. The results showed that transgenic perennial ryegrass plants displayed morphological changes under normal growth conditions, such as curl leaves and sunken stomata, which could be related to decreased leaf water loss. Moreover, transgenic perennial ryegrass exhibited improved drought tolerance, as demonstrated by maintaining higher leaf relative water content (RWC), lower electrolyte leakage (EL), and less lipid peroxidation compared to WT plants under drought stress. Furthermore, the transgenic plants showed higher antioxidative capacity under drought. These results showed that the improved drought tolerance in Os-miR408 transgenic plants could be due to leaf morphological changes favoring the maintenance of water status and to increased antioxidative capacity protecting against the reactive oxygen species damages under stress. These findings implied that miR408 could serve as a potential target for genetic manipulations to engineer perennial grass plants for improved water stress tolerance.

Unravelling Differences in Candidate Genes for Drought Tolerance in Potato (Solanum tuberosum L.) by Use of New Functional Microsatellite Markers

Potato is regarded as drought sensitive and most vulnerable to climate changes. Its cultivation in drought prone regions or under conditions of more frequent drought periods, especially in subtropical areas, requires intensive research to improve drought tolerance in order to guarantee high yields under limited water supplies. A candidate gene approach was used to develop functional simple sequence repeat (SSR) markers for association studies in potato with the aim to enhance breeding for drought tolerance. SSR primer combinations, mostly surrounding interrupted complex and compound repeats, were derived from 103 candidate genes for drought tolerance. Validation of the SSRs was performed in an association panel representing 34 mainly starch potato cultivars. Seventy-five out of 154 SSR primer combinations (49%) resulted in polymorphic, highly reproducible banding patterns with polymorphic information content (PIC) values between 0.11 and 0.90. Five SSR markers identified allelic differences between the potato cultivars that showed significant associations with drought sensitivity. In all cases, the group of drought-sensitive cultivars showed predominantly an additional allele, indicating that selection against these alleles by marker-assisted breeding might confer drought tolerance. Further studies of these differences in the candidate genes will elucidate their role for an improved performance of potatoes under water-limited conditions.

Transcriptomic and metabolomic analyses of non-structural carbohydrates in red maple leaves

Plant sugars serve to balance nutrition, regulate development, and respond to biotic and abiotic stresses, whereas non-structural carbohydrates (NSCs) are essential energy sources that facilitate plant growth, metabolism, and environmental adaptation. To better elucidate the mechanisms of NSCs in red maple, ultrahigh-performance liquid chromatograph Q extractive mass spectrometry (UHPLC-QE-MS) and high-throughput RNA-sequencing were performed on green, red, and yellow leaves from a selected red maple mutant. In green leaves, the fructose phosphorylation process exhibited greater flux. In yellow leaves, sucrose and starch had a stronger capacity for synthesis and degradation, whereas in red leaves, there was a greater accumulation of trehalose and manninotriose. ArTPS5 positively regulated amylose, which was negatively regulated by ArFBP2, whereas ArFRK2 and ArFBP13 played a positive role in the biosynthesis of Sucrose-6P. Sucrose-6P also regulated anthocyanins and abscisic acid in red maple by affecting transcription factors. The results of this paper can assist with the control and optimization of the biosynthesis of NSCs in red maple, which may ultimately provide the foundation for influencing sugar production in Acer.

Physiological responses and expression of sugar associated genes in faba bean (Vicia faba L.) exposed to osmotic stress

Faba bean (Vicia faba L.) is the major food legume crop in Tunisia. However, its growth and yield is strongly affected by water-limited environments. In this study, osmotic stress exhibited a negative effect on Bachar and Badii cultivar. Nevertheless, the deteriorating effects of osmotic stress were relatively low on studied parameters of Bachar due to its better efficiency to reduce oxidative damage by increasing enzymatic activities such as catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX), accumulation of total chlorophyll (Chlt), soluble sugars and leaf relative water content (RWC). GC-MS analysis determined a total of 11 soluble carbohydrates induced by osmotic stress and differentially accumulated in the both cultivars. Bachar showed elevated levels of mannose, glucose, galactose, ribose, rhamnose and myo-inositol which might help to maintain osmotic adjustment, membranes and proteins protection from the damaging effect of reactive oxygen species. Sugar metabolism related genes (VfNINV3, VfPHS2, VfFRK4, VfHXK1, VfGPI1, VfSTP1.1, VfpGlcT1.1, VfSTP5.1, VfpGlcT1.2, VfSWEET2.1, VfVINV2, VfSUS1, VfPGM1, VfSUT1.1, VfGPT1, VfSPS1, VfSPP1, VfPHS1, VfSUT4.1 and VfTMT1.1) were differentially expressed in both cultivars demonstrating their important roles in sugar accumulation. Most of these genes were upregulated in the leaves of Bachar under moderate and severe stress, which could lead to increase glycolysis and tricarboxylic acid cycle in order to accelerate energy production, necessary to increase osmotic regulation and consequently enhancing the osmotic stress tolerance in that cultivar. Overall, sugars accumulation ability can be used as a useful indicator for the osmotic stress tolerant potential in faba bean breeding programs.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s12298-021-00935-1).

Identification of metabolites associated with water stress responses in Solanum tuberosum L. clones

Water deficiency has become a major issue for modern agriculture as its effects on crop yields and tuber quality have become more pronounced. Potato genotypes more tolerant to water shortages have been identified through assessment of yield and dry matter. In the present study, a combination of metabolite profiling and physiological/agronomical measurements has been used to explore complex system level responses to non-lethal water restriction. The metabolites identified were associated with physiological responses in three different plant tissues (leaf, root and tuber) of five different potato genotypes varying in susceptibility/tolerance to drought. This approach explored the potential of metabolite profiling as a tool to unravel sectors of metabolism that react to stress conditions and could mirror the changes in the plant physiology. The metabolite results showed different responses of the three plant tissues to the water deficit, resulting either in different levels of the metabolites detected or different metabolites expressed. The leaf material displayed the most changes to drought as reported in literature. The results highlighted genotype-specific signatures to water restriction over all three plant tissues suggesting that the genetics can predominate over the environmental conditions. This will have important implications for future breeding approaches.

The drought response of potato reference cultivars with contrasting tolerance

Systems responses to drought stress of four potato reference cultivars with differential drought tolerance (Solanum tuberosum L.) were investigated by metabolome profiling and RNA sequencing. Systems analysis was based on independent field and greenhouse trials. Robust differential drought responses across all cultivars under both conditions comprised changes of proline, raffinose, galactinol, arabitol, arabinonic acid, chlorogenic acid and 102 transcript levels. The encoded genes contained a high proportion of heat shock proteins and proteins with signalling or regulatory functions, for example, a homolog of abscisic acid receptor PYL4. Constitutive differences of the tolerant compared with the sensitive cultivars included arbutin, octopamine, ribitol and 248 transcripts. The gene products of many of these transcripts were pathogen response related, such as receptor kinases, or regulatory proteins, for example, a homolog of the Arabidopsis FOUR LIPS MYB-regulator of stomatal cell proliferation. Functional enrichment analyses imply heat stress as a major acclimation component of potato leaves to long-term drought stress. Enhanced heat stress during drought can be caused by loss of transpiration cooling. This effect and CO₂ limitation are the main consequences of drought-induced or abscisic acid-induced stomatal closure. Constitutive differences in metabolite and transcript levels between tolerant and sensitive cultivars indicate interactions of drought tolerance and pathogen resistance in potato.

High-Density Genetic Mapping Identifies New Major Loci for Tolerance to Low-Phosphorus Stress in Soybean

Phosphorus (P) is essential for all living cells and organisms, and low-P stress represents a major constraint on plant growth and yield worldwide. Soybean is an important economical resource of protein and oil for human and animals, and soybean is also a high-P demand species that is sensitive to low-P stress, which is considered a major constraint on soybean production. However, P efficiency is an important complex quantitative trait involving multiple genes, and the mechanisms underlying soybean P efficiency are largely unknown. Here, we reported the construction of a high-density genetic map using a specific-locus amplified fragment sequencing (SLAF-seq) strategy in soybean. This map, spanning 3020.59 cM in length, contained 6159 markers on 20 chromosomes, with an average distance of 0.49 cM between adjacent markers. Based on this map, 20 loci, including eight novel loci, associated with P efficiency-related traits were identified across multiple years and treatments. The confidence intervals of almost all QTLs were refined significantly, and the accuracy of this map was evidenced by coincident detections of the previously identified P efficiency-related genes GmACP1 and GmPT1. Notably, a highly significant novel QTL located on chromosome 4, q4-2, was identified across traits, years and treatments. Several candidate genes, such as a pectin methylesterase-encoding gene (Glyma.04G214000) and a protein kinase gene (Glyma.13G161900), with significantly differential expression upon low-P stress were considered as promising candidates involved in regulating soybean P efficiency. Markers that tightly associated with P efficiency could be used for marker-assisted selection in a soybean P efficient breeding program. Further, dissection of these QTLs will facilitate gene cloning underlying P efficiency in soybean, and increase our understanding of efficient use of P in enhancing crop yield.

Unravelling the effect of sucrose and cold pretreatment on cryopreservation of potato through sugar analysis and proteomics

Apical shoot tips were dissected from donor plants (cultured in several conditions) and cryopreserved using the droplet-vitrification technique. The effect of two preculture treatments (sucrose pretreatment medium or cold-culturing during two weeks) on donor plants of four potato species (Solanum commersonii, S. juzepcukii, S. ajanhuiri, and Solanum tuberosum) was studied. Post-cryopreservation meristem growth and plant recovery were influenced by the treatments, but the effect on the regeneration was strongly genotype-dependent. The highest post-rewarming plant recovery percentage was obtained using meristems dissected from donor plants of S. commersonii cultured on sucrose pretreatment medium or cold-cultured. Both preculture conditions also enhanced plant recovery in S. juzepcukii compared to control cultures. Cold preculture, however, proved to be undesirable for S. tuberosum whereas sucrose pretreatment had a positive impact on the plant regeneration of this species. The determination of changes in the concentration of soluble sugars revealed sugar accumulation, especially of sucrose and the raffinose family of oligosaccharides (RFOs), which can be linked to tolerance towards the cryopreservation. Additionally, a study of the proteome of the donor plantlets after the pretreatments by 2D-fluorescence difference gel electrophoresis (DIGE) was carried out to identify differentially abundant proteins. Carbon metabolism-related proteins, together with stress-response and oxidative-homeostasis related proteins were the main class of proteins that changed in abundance after the pretreatments. Our results suggest that oxidative homeostasis-related proteins and sugars may be associated with the improved tolerance to cryopreservation and the ability to cold acclimate by S. commersonii in contrast to the other genotypes. The increased accumulation of sucrose and RFOs play a fundamental role in the response to stress in potato and may help to acquire tolerance to cryopreservation.

Improving potato drought tolerance through the induction of long-term water stress memory

Knowledge of drought tolerance in potato is limited and very little is known about stress memory in this crop. In the present study, long-term stress memory was tested on tuber yield and drought tolerance related traits in three potato varieties (Unica, Désirée and Sarnav) with contrasted yields under water restriction. Seed tubers produced by plants grown under non-restricted (non-primed tubers) and restricted (primed tubers) water conditions were sown and exposed to similar watering treatments. Tuber yield and leaf greenness of plants from primed and non-primed seeds as well as tuber carbon isotope discrimination (Δ(13)C) and antioxidant activity (AA) responses to watering treatments were compared. Higher tuber yield, both under non-restricted and restricted water regimes, was produced by primed Sarnav plants. The decrease of tuber yield and Δ(13)C with water restriction was lower in primed Unica plants. Long-term stress memory consequently appears to be highly genotype-dependent in potato. Its expression in plants originated from primed tubers and facing water restriction seems to be positively associated to the degree of inherent capability of the cultivar to yield under water restriction. However, other effects of priming appear to be genotype-independent as priming enhanced the tuber AA in response to water restriction in the three varieties.

Coping with drought: stress and adaptive responses in potato and perspectives for improvement

Potato (Solanum tuberosum L.) is often considered as a drought sensitive crop and its sustainable production is threatened due to frequent drought episodes. There has been much research aiming to understand the physiological, biochemical, and genetic basis of drought tolerance in potato as a basis for improving production under drought conditions. The complex phenotypic response of potato plants to drought is conditioned by the interactive effects of the plant's genotypic potential, developmental stage, and environment. Effective crop improvement for drought tolerance will require the pyramiding of many disparate characters, with different combinations being appropriate for different growing environments. An understanding of the interaction between below ground water uptake by the roots and above ground water loss from the shoot system is essential. The development of high throughput precision phenotyping platforms is providing an exciting new tool for precision screening, which, with the incorporation of innovative screening strategies, can aid the selection and pyramiding of drought-related genes appropriate for specific environments. Outcomes from genomics, proteomics, metabolomics, and bioengineering advances will undoubtedly compliment conventional breeding strategies and presents an alternative route toward development of drought tolerant potatoes. This review presents an overview of past research activity, highlighting recent advances with examples from other crops and suggesting future research directions.

Microarray analysis of gene expression patterns in the leaf during potato tuberization in the potato somatic hybrid Solanum tuberosum and Solanum etuberosum

Genes involved in photoassimilate partitioning and changes in hormonal balance are important for potato tuberization. In the present study, we investigated gene expression patterns in the tuber-bearing potato somatic hybrid (E1-3) and control non-tuberous wild species Solanum etuberosum (Etb) by microarray. Plants were grown under controlled conditions and leaves were collected at eight tuber developmental stages for microarray analysis. A t-test analysis identified a total of 468 genes (94 up-regulated and 374 down-regulated) that were statistically significant (p ≤ 0.05) and differentially expressed in E1-3 and Etb. Gene Ontology (GO) characterization of the 468 genes revealed that 145 were annotated and 323 were of unknown function. Further, these 145 genes were grouped based on GO biological processes followed by molecular function and (or) PGSC description into 15 gene sets, namely (1) transport, (2) metabolic process, (3) biological process, (4) photosynthesis, (5) oxidation-reduction, (6) transcription, (7) translation, (8) binding, (9) protein phosphorylation, (10) protein folding, (11) ubiquitin-dependent protein catabolic process, (12) RNA processing, (13) negative regulation of protein, (14) methylation, and (15) mitosis. RT-PCR analysis of 10 selected highly significant genes (p ≤ 0.01) confirmed the microarray results. Overall, we show that candidate genes induced in leaves of E1-3 were implicated in tuberization processes such as transport, carbohydrate metabolism, phytohormones, and transcription/translation/binding functions. Hence, our results provide an insight into the candidate genes induced in leaf tissues during tuberization in E1-3.

Spermine alleviates drought stress in white clover with different resistance by influencing carbohydrate metabolism and dehydrins synthesis

The objective of this research was to analyse whether ameliorating drought stress through exogenously applied spermine (Spm) was related to carbohydrate metabolism, dehydrins accumulation and the transcription of genes encoding dehydrins in two white clovers (drought-susceptible cv. ‘Ladino’ and drought-resistant cv. ‘Haifa’) under controlled drying conditions for 10 days. The results show that the application of Spm effectively alleviates negative effects caused by drought stress in both cultivars. Exogenous Spm led to accumulation of more water-soluble carbohydrates (WSC), sucrose, fructose and sorbitol in both cultivars under drought stress, and also significantly elevated glucose content in leaves of drought-resistant cv. ‘Haifa’, but had no effect on drought-susceptible cv. ‘Ladino’. Accordingly, the key enzyme activities of sucrose and sorbitol metabolism changed along with the application of Spm under drought stress. Spm induced a significant increase in sucrose phosphate synthase (SPS) or sorbitol dehydrogenase (SDH) activity, but decrease in sucrose synthetase (SS) activity when two cultivars were subjected to drought. In addition, the improved accumulation of dehydrins induced by exogenous Spm coincided with three genes expression which was responsible for dehydrins synthesis. But Spm-induced transcript level of dehydrin genes increased earlier in cv. ‘Ladino’ than that in cv. ‘Haifa’. Thus, these results suggest that ameliorating drought stress through exogenously applied Spm may be associated with increased carbohydrate accumulation and dehydrins synthesis. There are differences between drought-susceptible and -resistant white clover cultivars related to Spm regulation of WSC metabolism and dehydrins expression.

Differential Protein Expression in Response to Abiotic Stress in Two Potato Species: Solanum commersonii Dun and Solanum tuberosum L

Better knowledge on responses to dehydration stress could help to improve the existing cryopreservation protocols for potato, since plant tissues processed for cryopreservation are often submitted to similar in vitro stress conditions. Cryopreservation (the best method of conservation for vegetatively propagated plants) of potato still needs to be standardized to make it available and to conserve the wide diversity of this crop. In the present work, the response to osmotic stress and chilling temperature was investigated in two potato species, Solanum tuberosum and its relative, frost-tolerant S. commersonii. After 14 days of exposure, different growth parameters, such as shoot length and number of leaves, were measured. Furthermore, differentially abundant proteins were identified after performing 2-fluorescence difference gel electrophoresis (2-DIGE) experiments, and soluble carbohydrates were analyzed by High Performance Anion Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD). The results show different responses in both species depending on the stress treatment. Focusing on the differences in growth parameters during the treatments, Solanum commersonii seems to be more affected than S. tuberosum cv. Désirée. At the molecular level, there are some differences and similarities between the two potato species studied that are dependent on the type of stressor.

Effects of yeast trehalose-6-phosphate synthase 1 on gene expression and carbohydrate contents of potato leaves under drought stress conditions

BACKGROUND

The development of drought-tolerant, elite varieties of potato (Solanum tuberosum L.) is a challenging task, which might be achieved by introducing transgenic lines into breeding. We previously demonstrated that strains of the White Lady potato cultivar that express the yeast trehalose-6-phosphate synthase (TPS1) gene exhibit improved drought tolerance.

RESULTS

We investigated the responses of the drought-sensitive potato cultivar White Lady and the drought-tolerant TPS1 transgenic variant to prolonged drought stress at both the transcriptional and metabolic levels. Leaf mRNA expression profiles were compared using the POCI microarray, which contains 42,034 potato unigene probes. We identified 379 genes of known function that showed at least a 2-fold change in expression across genotypes, stress levels or the interaction between these factors. Wild-type leaves had twice as many genes with altered expression in response to stress than TPS1 transgenic leaves, but 112 genes were differentially expressed in both strains. We identified 42 transcription factor genes with altered expression, of which four were uniquely up-regulated in TPS1 transgenic leaves. The majority of the genes with altered expression that have been implicated in photosynthesis and carbohydrate metabolism were down-regulated in both the wild-type and TPS1 transgenic plants. In agreement with this finding, the starch concentration of the stressed leaves was very low. At the metabolic level, the contents of fructose, galactose and glucose were increased and decreased in the wild-type and TPS1 transgenic leaves, respectively, while the amounts of proline, inositol and raffinose were highly increased in both the wild-type and TPS1 transgenic leaves under drought conditions.

CONCLUSIONS

To our knowledge, this study is the most extensive transcriptional and metabolic analysis of a transgenic, drought-tolerant potato line. We identified four genes that were previously reported as drought-responsive in non-transgenic Andean potato cultivars. The substantial increases in proline, inositol and raffinose contents detected in both the wild-type and TPS1 transgenic leaves appears to be a general response of potatoes to drought stress. The four transcription factors uniquely up-regulated in TPS1 transgenic leaves are good candidates for future functional analyses aimed at understanding the regulation of the 57 genes with differential expression in TPS1 transgenic leaves.

Towards a synthetic view of potato cold and salt stress response by transcriptomic and proteomic analyses

Potato can suffer from several abiotic stresses such as cold temperature, high soil salinity, lack of water or heavy metal exposure, to name a few. They are known to affect plant growth as well as productivity, with differential regulations at several levels. Potato response to cold and salt exposure was investigated at both transcriptomic and proteomic levels in a growth chamber experiment. Cold exposure in potato resulted in a higher number of significantly differentially regulated genes compared to salt exposure, whereas there were nearly three times more differentially regulated proteins after salt exposure when compared to cold exposure. The allocation of up and down-regulated genes at the functional category level also differed between salt and cold exposure although common trends, previously described in various abiotic stresses, were observed. In both stresses, the majority of photosynthesis-related genes were down-regulated whereas cell rescue and transcription factor-related genes were mostly up-regulated. In the other functional categories no common trend was observed; salt exposure results displayed a strong down-regulation of genes implicated in primary metabolism, detoxication apparatus and signal transduction, whereas upon cold exposure, up and down-regulated genes were similar in number. At the proteomic level, the abundance of the majority of identified proteins was increased except for the photosynthesis-related proteins, which were mostly less abundant after both salt and cold exposure. Common responses between salt and cold stress and specific responses inherent to these abiotic stresses are described.

Elevated cytokinin content in ipt transgenic creeping bentgrass promotes drought tolerance through regulating metabolite accumulation

Increased endogenous plant cytokinin (CK) content through transformation with an adenine isopentyl transferase (ipt) gene has been associated with improved plant drought tolerance. The objective of this study is to determine metabolic changes associated with elevated CK production in ipt transgenic creeping bentgrass (Agrostis stolonifera L.) with improved drought tolerance. Null transformants (NTs) and plants transformed with ipt controlled by a stress- or senescence-activated promoter (SAG12-ipt) were exposed to well-watered conditions or drought stress by withholding irrigation in an environmental growth chamber. Physiological analysis confirmed that the SAG12-ipt line (S41) had improved drought tolerance compared with the NT plants. Specific metabolite changes over the course of drought stress and differential accumulation of metabolites in SAG12-ipt plants compared with NT plants at the same level of leaf relative water content (47% RWC) were identified using gas chromatography-mass spectroscopy. The metabolite profiling analysis detected 45 metabolites differentially accumulated in response to ipt expression or drought stress, which included amino acids, carbohydrates, organic acids, and organic alcohols. The enhanced drought tolerance of SAG12-ipt plants was associated with the maintenance of accumulation of several metabolites, particularly amino acids (proline, γ-aminobutyric acid, alanine, and glycine) carbohydrates (sucrose, fructose, maltose, and ribose), and organic acids that are mainly involved in the citric acid cycle. The accumulation of these metabolites could contribute to improved drought tolerance due to their roles in the stress response pathways such as stress signalling, osmotic adjustment, and respiration for energy production.

Alteration in expression of hormone-related genes in wild emmer wheat roots associated with drought adaptation mechanisms

Transcriptomic and metabolomic profiles were used to unravel drought adaptation mechanisms in wild emmer wheat (Triticum turgidum ssp. dicoccoides), the progenitor of cultivated wheat, by comparing the response to drought stress in roots of genotypes contrasting in drought tolerance. The differences between the drought resistant (R) and drought susceptible (S) genotypes were characterized mainly by shifts in expression of hormone-related genes (e.g., gibberellins, abscisic acid (ABA) and auxin), including biosynthesis, signalling and response; RNA binding; calcium (calmodulin, caleosin and annexin) and phosphatidylinositol signalling, in the R genotype. ABA content in the roots of the R genotype was higher in the well-watered treatment and increased in response to drought, while in the S genotype ABA was invariant. The metabolomic profiling revealed in the R genotype a higher accumulation of tricarboxylic acid cycle intermediates and drought-related metabolites, including glucose, trehalose, proline and glycine. The integration of transcriptomics and metabolomics results indicated that adaptation to drought included efficient regulation and signalling pathways leading to effective bio-energetic processes, carbon metabolism and cell homeostasis. In conclusion, mechanisms of drought tolerance were identified in roots of wild emmer wheat, supporting our previous studies on the potential of this genepool as a valuable source for novel candidate genes to improve drought tolerance in cultivated wheat.