ABA Levels Research Articles

Transcriptomic and metabolomic profiling of drought-tolerant and susceptible sesame genotypes in response to drought stress

BackgroundSesame is an important oil crop due to its high oil, antioxidant, and protein content. Drought stress is a major abiotic stress that affects sesame production as well as the quality of sesame seed. To reveal the adaptive mechanism of sesame in response to water deficient conditions, transcriptomic and metabolomics were applied in drought-tolerant (DT) and drought-susceptible (DS) sesame genotypes.ResultsTranscriptomic analysis reveals a set of core drought-responsive genes (684 up-regulated and 1346 down-regulated) in sesame that was robustly differently expressed in both genotypes. Most enriched drought-responsive genes are mainly involved in protein processing in endoplasmic reticulum, plant hormone signal transduction photosynthesis, lipid metabolism, and amino acid metabolism. Drought-susceptible genotype was more disturbed by drought stress at both transcriptional and metabolic levels, since more drought-responsive genes/metabolites were identified in DS. Drought-responsive genes associated with stress response, amino acid metabolism, and reactive oxygen species scavenging were more enriched or activated in DT. According to the partial least-squares discriminate analysis, the most important metabolites which were accumulated under drought stress in both genotypes includes ABA, amino acids, and organic acids. Especially, higher levels of ABA, proline, arginine, lysine, aromatic and branched chain amino acids, GABA, saccharopine, 2-aminoadipate, and allantoin were found in DT under stress condition. Combination of transcriptomic and metabolomic analysis highlights the important role of amino acid metabolism (especially saccharopine pathway) and ABA metabolism and signaling pathway for drought tolerance in sesame.ConclusionThe results of the present study provide valuable information for better understanding the molecular mechanism underlying drought tolerance of sesame, and also provide useful clues for the genetic improvement of drought tolerance in sesame.

Effects of exogenous ABA on translocation of photosynthate to fruit of Fuji apple during late stage of fruit rapid-swelling.

To clarify the effects and underlying mechanism of ABA on sugar accumulation in apple fruits, 13C trace technique was used to examined the effects of different ABA levels (0, 50, 100 and 150 mg·L-1) and fluoridone (ABA biosynthesis inhibitor) on translocation of photosynthate to fruit during late stage of fruit rapid-swelling in five-year-old 'Yanfu3'/M26/Malus hupehensis Rehd. The results showed that the activities of related enzyme in sugar metabolism, the relative expression of sucrose transporter gene MdSUT1, MdSUT2.2 and sorbitol transporter gene MdSOT3 tended to increase first and then decrease with increasing ABA concentration, with a peak in 100 mg·L-1ABA treatment. Fluridone treatment significantly inhibited the enzymes activities of sugar metabolism and the relative expression of sugar transporters. The treatment of 100 mg·L-1ABA significantly reduced leaf 13C content, increased fruit 13C content and increased the transport rate of photosynthate from leaves to fruits compared with other treatments. Our results indicated that exogenous ABA enhanced sink strength of fruit and promoted the transportation of more photosynthate to fruits, which increased the soluble sugar content in fruits.

Regulation of Antioxidant Enzymes and Invertases by Hydrogen Peroxide and Nitric Oxide Under ABA and Water-Deficit Stress in Wheat

The present investigation reports the activities of different antioxidant enzymes and invertases (acid, alkaline and cell wall bound) in shoots and roots of 5.5-day-old seedlings of wheat cultivars PBW 644 (drought tolerant and ABA higher sensitive) and PBW 343 (drought susceptible and ABA lesser sensitive) under ABA and water-deficit stress in the presence of H2O2/nitric oxide (NO) donors as well as scavengers. Drought stress was produced by 20% PEG 6000. Sodium nitroprusside as NO donor and dimethylthiourea and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) as H2O2 and NO scavengers, respectively, were used. Roots of PBW 644 increased activities of antioxidant enzymes and invertases (acid and alkaline) and sucrose content, while PBW 343 decreased these under PEG. This was related to the presence of endogenous H2O2/NO regulation of these parameters under PEG in roots of PBW 644 but deficient in roots of PBW 343 but improved under exogenous H2O2/NO for some parameters. However, compared to PEG, roots of PBW 343 showed endogenous H2O2/NO regulation of many these parameters under ABA. Under ABA, endogenous H2O2/NO regulation was comparable between cultivars. This study showed that H2O2/NO signalling plays an important role in drought tolerance by upregulating antioxidant enzymes and invertases under stress. ABA sensitivity level and ABA levels present in cells may help to produce an effective endogenous H2O2/NO signalling.

Exogenous application of glycine betaine improved water use efficiency in winter wheat (Triticum aestivum L.) via modulating photosynthetic efficiency and antioxidative capacity under conventional and limited irrigation conditions

Improving water use efficiency (WUE) is an important subject in agricultural irrigation for alleviating the scarcity of water resources in semiarid regions of the North China Plain. Moreover, glycine betaine (GB) is one of the most effective compatible solutes synthesized naturally in plants for enhancing stress tolerance under abiotic stress, but little information is available on the involvement of GB in regulating crop WUE under field conditions. This study was conducted to explore the role of exogenously applied GB in improving WUE and plant physiological and biochemical responses in winter wheat subjected to conventional or limited irrigation during the 2015–2016 and 2016–2017 growing seasons. Exogenous application of GB significantly enhanced antioxidant enzyme activities and reduced the accumulation of malondialdehyde and hydrogen peroxide under limited irrigation conditions. Furthermore, GB-treated plants maintained higher leaf relative water content and membrane stability, which led to higher chlorophyll content and gas exchange attributes for better intrinsic and instantaneous water use efficiencies compared to control plants under limited irrigation conditions. GB-treated plants had higher indole-acetic acid and zeatin riboside levels but lower ABA levels compared to control plants under conventional and limited irrigation conditions. Additionally, GB enhanced the grain filling rate and duration, grain number per spike, and final grain weight, which resulted in higher grain yield compared to the control. Interestingly, GB significantly improved the integrative and photosynthetic WUE under conventional and limited irrigation conditions, although GB treatment did not markedly affect total water consumption. These results suggest the involvement of GB in improving WUEs in winter wheat by modulating hormonal balance, membrane stability, photosynthetic performance and antioxidant systems to maintain higher grain yield under conventional and limited irrigation conditions.

The bZIP73 transcription factor controls rice cold tolerance at the reproductive stage.

SummaryCold temperature during the reproductive stage often causes great yield loss of grain crops in subtropical and temperate regions. Previously we showed that the rice transcription factor bZIP73Jap plays an important role in cold adaptation at the seedling stage. Here we further demonstrate that bZIP73Jap also confers cold stress tolerance at the reproductive stage. bZIP73 Jap was up‐regulated under cold treatment and predominately expressed in panicles at the early binucleate and flowering stages. bZIP73Jap forms heterodimers with bZIP71, and co‐expression of bZIP73 Jap and bZIP71 transgenic lines significantly increased seed‐setting rate and grain yield under natural cold stress conditions. bZIP73Jap:bZIP71 not only repressed ABA level in anthers, but also enhanced soluble sugar transport from anthers to pollens and improved pollen grain fertility, seed‐setting rate, and grain yield. Interestingly, bZIP73Jap:bZIP71 also regulated the expression of qLTG3‐1 Nip, and qLTG3‐1 Nip overexpression lines greatly improved rice tolerance to cold stress during the reproductive stage. Therefore, our work establishes a framework for rice cold stress tolerance through the bZIP71‐bZIP73Jap‐qLTG3‐1Nip‐sugar transport pathway. Together with our previous work, our results provide a powerful tool for improving rice cold stress tolerance at both the seedling and the reproductive stages.

ICE1 and ZOU determine the depth of primary seed dormancy in Arabidopsis independently of their role in endosperm development.

SummarySeed dormancy is a widespread and key adaptive trait that is essential for the establishment of soil seed banks and prevention of pre‐harvest sprouting. Herein we demonstrate that the endosperm‐expressed transcription factors ZHOUPI (ZOU) and INDUCER OF CBF EXPRESSION1 (ICE1) play a role in determining the depth of primary dormancy in Arabidopsis. We show that ice1 or zou increases seed dormancy and the double mutant has an additive phenotype. This increased dormancy is associated with increased ABA levels, and can be separated genetically from any role in endosperm maturation because loss of ABA biosynthesis or DELAY OF GERMINATION 1 reverses the dormancy phenotype without affecting the aberrant seed morphology. Consistent with these results, ice1 endosperms had an increased capacity for preventing embryo greening, a phenotype previously associated with an increase in endospermic ABA levels. Although ice1 changes the expression of many genes, including some in ABA biosynthesis, catabolism and/or signalling, only ABA INSENSITIVE 3 is significantly misregulated in ice1 mutants. We also demonstrate that ICE1 binds to and inhibits expression of ABA INSENSITIVE 3. Our data demonstrate that Arabidopsis ICE1 and ZOU determine the depth of primary dormancy during maturation independently of their effect on endosperm development.

Transcriptomic analysis of grain filling in rice inferior grains under moderate soil drying.

Moderate soil drying imposed at the post-anthesis stage significantly increases starch accumulation in inferior grains of rice, but how this process is regulated at the level of gene expression remains unclear. In this study, we applied moderate drying (MD) treatments to the soil at the post-anthesis stage and followed the dynamics of the conversion process of soluble sugars to starch in inferior grains using RNA-seq analysis. An elevated level of ABA induced by MD was consistently associated with down-regulation of ABA8ox2, suggesting that lower expression of this gene may be responsible for the higher ABA content, potentially resulting in better filling in inferior grains. In addition, MD treatments up-regulated genes encoding five key enzymes involved sucrose-to-starch conversion and increased the activities of enzymes responsible for soluble-sugar reduction and starch accumulation in inferior grains. Differentially expressed transcription factors, including NAC, GATA, WRKY, and M-type MADS, were predicted to interact with other proteins in mediating filling of inferior grains as a response to MD. Transient expression analysis showed that NAC activated WAXY expression by binding to its promoter, indicating that NAC played a key role in starch synthesis of inferior grains under MD treatment. Our results provide new insights into the molecular mechanisms that regulate grain filling in inferior grains of rice under moderate soil drying.

Cytokinin-induced parthenocarpy of San Pedro type fig (Ficus carica L.) main crop: explained by phytohormone assay and transcriptomic network comparison.

CPPU-induced San Pedro type fig main crop parthenocarpy exhibited constantly increasing IAA content and more significantly enriched KEGG pathways in the receptacle than in female flowers. N-(2-chloro-4-pyridyl)-N-phenylurea (CPPU) was applied to San Pedro fig (Ficus carica L.) main crop to induce parthenocarpy; the optimal effect was obtained with 25mgL-1 application to syconia when female flowers were at anthesis. To elucidate the key expression changes in parthenocarpy conversion, significant changes in phytohormone level and transcriptome of fig female flowers and receptacles were monitored. HPLC-MS revealed increased IAA content in female flowers and receptacle 2, 4 and 10days after treatment (DAT), decreased zeatin level in the receptacle 2, 4 and 10 DAT, decreased GA3 content 2 and 4 DAT, and increased GA3 content 10 DAT. ABA level increased 2 and 4 DAT, and decreased 10 DAT. CPPU-treated syconia released more ethylene than the control except 2 DAT. RNA-Seq and bioinformatics analysis revealed notably more differentially expressed KEGG pathways in the receptacle than in female flowers. In the phytohormone gene network, GA-biosynthesis genes GA20ox and GA3ox were upregulated, along with GA signal-transduction genes GID1 and GID2, and IAA-signaling genes AUX/IAA and GH3. ABA-biosynthesis gene NCED and signaling genes PP2C and ABF were downregulated 10 DAT. One ACO gene showed consistent upregulation in both female flowers and receptacle after CPPU treatment, and more than a dozen of ERFs demonstrated opposing changes in expression. Our results revealed early-stage spatiotemporal phytohormone and transcriptomic responses in CPPU-induced San Pedro fig main crop parthenocarpy, which could be valuable for further understanding the nature of the parthenocarpy of different fig types.

ABA promotes starch synthesis and storage metabolism in dormant grapevine buds

In grapevine (Vitis vinifera L.) buds, the short day (SD)-photoperiod induces endodormancy and increases the level of ABA and the expression of ABA key biosynthesis genes, which suggests that ABA could be the mediator of the photoperiodic induction of endodormancy. In the present study, it was established that during the development of the endodormancy, the content of ABA and the accumulation of starch increased in parallel in the buds; however, these increases occurred after the buds were already in the state of endodormancy. Despite this finding the exogenous applications of ABA to single-bud cuttings increased the starch content and up-regulated the expression of starch synthesis genes (VvSS1 and VvSS3) and down-regulated the expression of sucrose metabolism genes, invertase (VvINV) and sucrose phosphate synthase (VvSUPS). In addition, the manipulation of the endogenous content of ABA in the grapevine buds by applications of hydrogen cyanamide and uniconazole-P, revealed that the depth of the endodormancy depends on the ABA levels. Taken together, the results indicate that the development of the endodormancy in grapevine buds is associated with the accumulation of starch and a shift in metabolism towards a storage metabolism; as ABA stimulates both processes, it must play an important role in the maintenance and release but not the induction of endodormancy in grapevine buds.

Water deficit and abscisic acid treatments increase the expression of a glucomannan mannosyltransferase gene (GMMT) in Aloe vera Burm. F.

The main polysaccharide of the gel present in the leaves of or Aloe vera Burm.F., (Aloe barbadensis Miller) a xerophytic crassulacean acid metabolism (CAM) plant, is an acetylated glucomannan named acemannan. This polysaccharide is responsible for the succulence of the plant, helping it to retain water. In this study we determined using polysaccharide analysis by carbohydrate gel electrophoresis (PACE) that the acemannan is a glucomannan without galactose side branches. We also investigated the expression of the gene responsible for acemannan backbone synthesis, encoding a glucomannan mannosyltransferase (GMMT, EC 2.4.1.32), since there are no previous reports on GMMT expression under water stress in general and specifically in Aloe vera. It was found by in silico analyses that the GMMT gene belongs to the cellulose synthase-like A type-9 (CSLA9) subfamily. Using RT-qPCR it was found that the expression of GMMT increased significantly in Aloe vera plants subjected to water stress. This expression correlates with an increase of endogenous ABA levels, suggesting that the gene expression could be regulated by ABA. To corroborate this hypothesis, exogenous ABA was applied to non-water-stressed plants, resulting in a significant increase of GMMT expression after 48 h of ABA treatment.

Overexpression of RcLEC1-B, a HAP3 transcription factor of PLB from Rosa canina, increases the level of endogenous gibberellin and alters the development of cuticle and floral organs in Arabidopsis

The HAP3 subfamily gene RcLEC1-B, was isolated from protocorm-like body (PLB) of Rosa canina, encodes 213 amino acid residues. It was shown that RcLEC1-B was specifically expressed in PLB of R. canina and its subcellular localization is in the nucleus. Overexpression of RcLEC1-B in Arabidopsis resulted in a decrease in endogenous ABA level, an increase in GA, IAA and CTK contents, and an increased number of branches. RcLEC1-B promotes the formation of spontaneous embryoids, suggesting that it may be a homolog of the Arabidopsis LEC1 gene. RcLEC1-B-OE changed the number and morphology of flower organs and resulted in open carpels and exposed ovules, along with a reduced percentage of fertile fruit. This is the first observation that overexpression of a homolog of LEC1 in Arabidopsis can lead to morphological changes in floral organs, cuticle defects, and adhesions between organs; this may result from the increased level of gibberellin in the transgenic plants.

Transient Heat Stress During Early Seed Development Primes Germination and Seedling Establishment in Rice.

Rice yield is highly sensitive to increased temperature. Given the trend of increasing global temperatures, this sensitivity to higher temperatures poses a challenge for achieving global food security. Early seed development in rice is highly sensitive to unfavorable environmental conditions. Heat stress (HS) during this stage decreases seed size and fertility, thus reducing yield. Here, we explore the transgenerational phenotypic consequences of HS during early seed development on seed viability, germination, and establishment. To elucidate the impact of HS on the developmental events in post-zygotic rice seeds, we imposed moderate (35°C) and severe (39°C) HS treatments initiated 1 day after fertilization and maintained for 24, 48, or 72 h. The transient HS treatments altered the initiation of endosperm (ED) cellularization, seed size and/or the duration of spikelet ripening. Notably, seeds exposed to 24 and 48 h moderate HS exhibited higher germination rate compared to seeds derived from plants grown under control or severe HS. A short-term HS resulted in altered expression of Gibberellin (GA) and ABA biosynthesis genes during early seed development, and GA and ABA levels and starch content at maturity. The increased germination rate after 24 of moderate HS could be due to altered ABA sensitivity and/or increased starch level. Our findings on the impact of transient HS on hormone homeostasis provide an experimental framework to elucidate the underlying molecular and metabolic pathways.

Overexpression of the RNA binding protein MhYTP1 in transgenic apple enhances drought tolerance and WUE by improving ABA level under drought condition

MhYTP1 is involved in post-transcriptional regulation as a member of YT521-homology (YTH) domain-containing RNA-binding proteins. We previously cloned MhYTP1 and found it participated in various biotic and abiotic stress responses. However, its function in long-term moderate drought has not been verified. Thus, we explored its biological role in response to drought. Under drought condition, the net photosynthesis rate (Pn) and water use efficiency (WUE) were significantly elevated in MhYTP1-overexpressing (OE) apple plants when compared with the non-transgenic (NT) controls. Further analysis indicated MhYTP1 expression was associated with elevated ABA content, increased stomatal density and reduced stomatal aperture. In addition, to gain insight into the function of stem-specific expression of MhYTP1, grafting experiments were performed. Interestingly, lower transpiration rate (Tr) and higher WUE were observed when transgenic plants were used as scions as opposed to rootstocks and when transgenic rather than NT plants were used as rootstocks, indicating MhYTP1 plays crucial roles in grafted plants. These results define a function for MhYTP1 in promoting tolerance to drought conditions, and suggest that MhYTP1 can serve as a candidate gene for future apple drought resistance breeding with the help of biotechnology.

Rust Infection of Black Poplar Trees Reduces Photosynthesis but Does Not Affect Isoprene Biosynthesis or Emission.

Poplar (Populus spp.) trees are widely distributed and play an important role in ecological communities and in forestry. Moreover, by releasing high amounts of isoprene, these trees impact global atmospheric chemistry. One of the most devastating diseases for poplar is leaf rust, caused by fungi of the genus Melampsora. Despite the wide distribution of these biotrophic pathogens, very little is known about their effects on isoprene biosynthesis and emission. We therefore infected black poplar (P. nigra) trees with the rust fungus M. larici-populina and monitored isoprene emission and other physiological parameters over the course of infection to determine the underlying mechanisms. We found an immediate and persistent decrease in photosynthesis during infection, presumably caused by decreased stomatal conductance mediated by increased ABA levels. At the same time, isoprene emission remained stable during the time course of infection, consistent with the stability of its biosynthesis. There was no detectable change in the levels of intermediates or gene transcripts of the methylerythritol 4-phosphate (MEP) pathway in infected compared to control leaves. Rust infection thus does not affect isoprene emission, but may still influence the atmosphere via decreased fixation of CO2.

Root colonization by Pseudomonas chlororaphis primes tomato (Lycopersicum esculentum) plants for enhanced tolerance to water stress

Previous research demonstrated that Pseudomonas chlororaphis subsp. aureofaciens strain M71, a plant growth promoting bacterium (PGPB), exerts beneficial effects on plant metabolism and primes tolerance mechanisms against biotic stresses in tomatoes. We designed an experiment to assess whether root colonization with P. chlororaphis is also able to improve tolerance to water stress in tomatoes. Our results show that inoculation with P. chlororaphis stimulates the antioxidant activity of well-watered tomatoes while maintaining a steady-state level of reactive oxygen species (ROS), increases the expression of genes encoding for the biosynthesis of leaf terpenes, stimulates the production of both the phytohormones ABA and IAA, in turn affecting plant shape (number of leaves) and height (length of internodes), without altering photosynthesis. Upon exposure to mild water stress conditions, an improved antioxidant activity in tomatoes ‘primed’ by P. chlororaphis inoculation limited the accumulation of reactive oxygen species (ROS) in leaves and thus enhanced tolerance, also through increase of the (osmolyte) proline content. Moreover, P. chlororaphis inoculation further enhanced the ABA level in leaves of water-stressed tomatoes allowing a more efficient modulation of stomatal closure that resulted in an improved water use efficiency (WUE) and biomass accumulation.

Hormone balance in a climacteric plum fruit and its non-climacteric bud mutant during ripening

Hormone balance plays a crucial role in the control of fruit ripening. We characterized and compared hormone balance in two Japanese plum cultivars (Prunus salicina Lindl.), namely Santa Rosa, a climacteric type, and Sweet Miriam, its non-climacteric bud-sport mutant. We assessed hormonal changes in gene expression associated with hormone biosynthesis, perception and signaling during ripening on-the tree and throughout postharvest storage and in response to ethylene treatments. Non-climacteric fruit displayed lower ethylene levels than climacteric fruit at all stages and lower auxin levels during the initiation of ripening on-the-tree and during most of post-harvest storage. Moreover, 1-MCP-induced ethylene decrease also resulted in low auxin contents in Santa Rosa, supporting the role of auxin in climacteric fruit ripening. The differences in auxin contents between Santa Rosa and Sweet Miriam fruit could be the consequence of different routed auxin biosynthesis pathways as indicated by the significant negative correlations between clusters of auxin metabolism-associated genes. Ethylene induced increased ABA levels throughout postharvest storage in both ripening types. Overall, ripening of Santa Rosa and Sweet Miriam fruit are characterized by distinct hormone accumulation pathways and interactions.

Three LcABFs are Involved in the Regulation of Chlorophyll Degradation and Anthocyanin Biosynthesis During Fruit Ripening in Litchi chinensis.

During litchi (Litchi chinensis Sonn.) fruit ripening, two major physiological changes, degreening (Chl degradation) and pigmentation (anthocyanin biosynthesis), are visually apparent. However, the specific factor triggering this important transition is still unclear. In the present study, we found that endogenous ABA content increased sharply when Chl breakdown was initiated and the ABA level peaked just before the onset of anthocyanin accumulation, suggesting that ABA plays an important role during litchi fruit pigmentation. We characterized three ABSCISIC ACID RESPONSE ELEMENT-BINDING FACTORs (LcABF1/2/3) belonging to group A of the basic leucine zipper (bZIP) transcription factors previously shown to be involved in ABA signaling under abiotic stress. LcABF1 transcripts increased at the onset of Chl degradation, and the expression of LcABF3 accumulated in parallel with anthocyanin biosynthesis. In addition, dual luciferase and yeast one-hybrid assays indicated that LcABF1/2 recognized ABA-responsive elements in the promoter region of Chl degradation-related genes (PAO and SGR), while LcABF2/3 bound the promoter region of LcMYB1 and anthocyanin biosynthesis-related structural genes. Indeed, Nicotiana benthamiana leaves transiently expressing LcABF1/2 showed a senescence phenomenon with Chl degradation, and LcABF3 overexpression increased the accumulation of anthocyanin via activation of LcMYB1, which is the key determinant of anthocyanin biosynthesis. These data indicate that LcABF1/2/3 are important transcriptional regulators of ABA-dependent litchi fruit ripening involved in both Chl degradation and anthocyanin biosynthesis.

Effects of incubation temperature on asparagus bud sprouting, abscisic acid content and sex

Dormancy in asparagus (Asparagus officinalis) spears depends on the growing temperature. It is crucial to understand the mechanism of the induction and break of dormancy related with bud sprouting of asparagus. During periods with low temperatures, the contents of several components; e.g. plant hormones in asparagus buds change and the plants acquire dormancy. Similarly, higher temperatures suppress sprouting. In this study, we investigated the effects of incubation temperatures on the sprouting rate of buds, growth of spears, ABA concentration and sex. During 22 days of low-temperature incubation, sprouting was not inhibited at 25°C, but it was almost inhibited at 16°C. The ABA concentrations of white bud clusters were higher at 16°C than at 25°C at the end of the incubation period, but they were not significantly different between male and female plants. The ABA concentrations were higher in brown than in white bud clusters, and they were similar among brown bud clusters at both 25 and 16°C. In the high-temperature incubation experiment, sprouting was slightly suppressed and growth rate of spears was significantly decreased at 38°C compared to those at 25°C. The ABA concentration of white bud clusters decreased gradually during the incubation at both 38 and 25°C, but that of brown bud clusters increased at both temperatures. Moreover, the ABA levels in both white and brown bud clusters from male plants fluctuated and they were higher compared to their levels in bud clusters from female plants. These results suggest that sprouting varied with the incubation temperature and may or may not be regulated by ABA.

Overexpression of MhYTP2 enhances apple water-use efficiency by activating ABA and ethylene signaling

A critical component of crop breeding is the identification of genes involved in improving water-use efficiency (WUE). We characterized MhYTP2, a gene cloned from Malus hupehensis that encodes an RNA-binding protein, to examine its role in WUE. Under both well-watered and drought conditions, overexpression of this gene enhanced WUE in transgenic plants and they accumulated more biomass than untransformed wild-type plants. This increase in WUE was probably due to enhancement of photosynthetic rate and root water uptake, and a reduction in stomatal aperture that resulted from elevated level of ABA and activated ethylene signaling. MhYTP2 was predominantly expressed in apple roots. We noted with interest that the rate of photosynthesis, instantaneous WUE, and root water potential were higher when 35S:MhYTP2 plants were used as rootstocks rather than as scions in our grafting experiments. Our results indicated that MhYTP2 has a more crucial role in the roots than in the aerial parts of the plant, and it implies that this gene can be used for improving WUE by apple rootstocks and, potentially, rootstocks of other graft-suitable crops.

Differential responses of two Iranian rice cultivars to arsenite toxicity

Arsenic (As) is a toxic metalloid which is usually found in rice fields as a contamination and has negative effects on the plant growth and reduces the crop yield. Similar to heavy metals, the deleterious effects of As may be due to, at least in part, the amount of absorbed As and disturbance of the plant water status. In this connection, different varieties of the same species may show differential performances. Comparative responses to 75 µM AsIII were evaluated in two Iranian rice cultivars adapted to moderate-humid vs. very warm and dry climates (Hashemi and Amber, respectively). Although both cultivars absorbed AsIII, but its translocation factor was lower in Amber accompanied by accumulation of soluble sugars and glycine betaine and lower level of internal ABA. Moreover, adverse effect of AsIII onrelative water content and stomata closure was less prominent in Amber, compared to Hashemi. Results suggest that cultivars adapted to dry conditions are more capable to withstand against As and to control its entrance to human food chain.