Positive feedback regulation of a Lycium chinense-derived VDE gene by drought-induced endogenous ABA, and over-expression of this VDE gene improve drought-induced photo-damage in Arabidopsis

ABA spray on Arabidopsis seedlings increases mature plants vigor under optimal and water-deficit conditions partly by enhancing nitrogen assimilation

Here, we report the effects of a single abscisic acid (ABA) spray on Arabidopsis seedlings on growth, development, primary metabolism, and response to water-deficit stress in adult and next-generation plants. The experiments were performed over 2 years in two different laboratories in Iran and South Africa. In each experiment, fifty 7-day-old Arabidopsis seedlings were sprayed with 10 μM ABA, 1 mM H2 O2 , distilled water, or left without spraying as priming treatments. Water-deficit stress was applied on half of the plants in each treatment by withholding water 2 days after spraying. Results showed that a single ABA spray at the cotyledonary stage significantly increased plant biomass and delayed flowering. The ABA spray significantly enhanced drought tolerance so that the survival rate after rehydration was 100 and 33% in the first and the second experiments, respectively, for ABA-treated plants compared to 35 and 0% for water-sprayed plants. This enhanced drought tolerance was not inheritable. Metabolomics analyses suggested that ABA probably increases the antioxidant capacity of the plant cells and modulates tricarboxylic acid cycle toward enhanced nitrogen assimilation. Strikingly, we also observed that the early water spray decreases mature plant resilience under water-deficit conditions and cause substantial transient metabolomics perturbations.

The potential roles of carotenoids in enhancing phytoremediation of bisphenol A contaminated soil by promoting plant physiology and modulating rhizobacterial community of tobacco

The widespread occurrence of bisphenol A (BPA), a typical endocrine-disrupting compound, poses potential threat to ecosystem and public health. Carotenoids are essential natural pigments, playing important roles in photosynthesis and antioxidant defense of plants. This study aimed to verify the value of carotenoids in enhancing plant tolerance to BPA stress and improving phytoremediation efficiency of tobacco (Nicotiana tabacum L.), through exogenous application of β-carotene (a typical carotenoid) and endogenous upregulation of carotenoids by overexpression of β-carotene hydroxylase (chyb) gene in tobacco. The results demonstrated that exogenous applied β-carotene alleviated the toxic effects of BPA exposure (100 mg kg^-1) on wild-type (WT) tobacco plants after being cultivated for 40 d, reflecting by the increase of biomass (201.2%), chlorophyll content (27.5%) and the decrease of malondialdehyde (MDA) content (70.7%). Similar with the results of exogenous application of β-carotene, chyb gene overexpressing tobacco showed less phytotoxicity exposed to BPA, through enhancing photosynthetic efficiency (42.1%) and reducing reactive oxygen species (ROS) production (18%). Notably, about 94.8% BPA in contaminated soil was removed under the cultivation of transgenic tobacco for 40 d, however, only 82.7% was removed in that of WT tobacco. Moreover, transgenic tobacco is beneficial for the growth of plant roots, thus upregulating the abundance of bacteria contributing to BPA degradation or soil nutrient cycling (e.g., Proteobacteria, Acidobacteria, Actinobacteria, Sphingomonas and MND1), which might further help to enhance plant growth and improve BPA removal efficiency in soil. This study extended our understanding of the possible mechanisms of carotenoids-involved alleviation of BPA stress in tobacco, providing a novel strategy to improve phytoremediation efficiency of plants in BPA contaminated soil.

Impacts of Radio-Frequency Electromagnetic Field (RF-EMF) on Lettuce (Lactuca sativa)-Evidence for RF-EMF Interference with Plant Stress Responses

The increased use of wireless technology causes a significant exposure increase for all living organisms to radio frequency electromagnetic fields (RF-EMF). This comprises bacteria, animals, and also plants. Unfortunately, our understanding of how RF-EMF influences plants and plant physiology remains inadequate. In this study, we examined the effects of RF-EMF radiation on lettuce plants (Lactuca sativa) in both indoor and outdoor environments using the frequency ranges of 1890-1900 MHz (DECT) at 2.4 GHz and 5 GHz (Wi-Fi). Under greenhouse conditions, RF-EMF exposure had only a minor impact on fast chlorophyll fluorescence kinetics and no effect on plant flowering time. In contrast, lettuce plants exposed to RF-EMF in the field showed a significant and systemic decrease in photosynthetic efficiency and accelerated flowering time compared to the control groups. Gene expression analysis revealed significant down-regulation of two stress-related genes in RF-EMF-exposed plants: violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). RF-EMF-exposed plants had lower Photosystem II's maximal photochemical quantum yield (F_V/F_M) and non-photochemical quenching (NPQ) than control plants under light stress conditions. In summary, our results imply that RF-EMF might interfere with plant stress responses and reduced plant stress tolerance.

Phytoremediation potential, antioxidant response, photosynthetic behavior and rhizosphere bacterial community adaptation of tobacco (Nicotiana tabacum L.) in a bisphenol A-contaminated soil

Bisphenol A (BPA) is an emerging organic pollutant, widely distributed and frequently detected in soil in recent years. BPA toxicity is a problem that needs to be solved in terms of both human health and agricultural production. Up to now, the toxic effect of BPA and its mechanism of action on plants, as well as the possibility of using plants to remediate BPA-contaminated soil, remain to be explored. In this study, six treatment groups were set up to evaluate the effects of different concentrations of BPA on the germination and growth of tobacco (Nicotiana tabacum L.) by medium experiments. Furthermore, the representative indexes of photosynthetic and antioxidant system were determined. Meanwhile, tobacco seedlings were cultivated in soil to further explore the effects of BPA on rhizosphere soil enzyme activity and bacterial community structure with or without 100 mg/kg BPA exposure. The enhancement of BPA removal efficiency from soil by phytoremediation using tobacco plants would also be estimated. Our results showed that high doses of BPA in solid medium remarkably inhibited tobacco seedling growth, and its toxicology effect was positively correlated with BPA concentration, while lower BPA exposure (< 20 mg/L) had little limitation on tobacco growth and induced hormesis effect, which was reflected mainly in the increase of root length. In pot experiments, the reducing of chlorophyll content (36.4%) and net photosynthetic rate (41.2%) meant the inhibition of tobacco photosynthetic process due to high concentration of BPA exposure (100 mg/kg) in soil. The increase of H2O2 and O2- content suggested that BPA could destroy the balance of reactive oxygen species (ROS) in plants. However, tobacco plants still presented a high removal efficiency of BPA at the concentration of 100 mg/kg in soil, which could reach to 80% within 30 days. Furthermore, it was indicated that tobacco cultivation changed the structure of rhizosphere soil bacterial communities and the relative abundance of some valuable strains, including Proteobacteria, Acidobacteria and other strains, which might be participated in the BPA removal process. In addition, the tobacco-soil microbial system had the potential to reverse the negative effects caused by BPA through stimulating microorganism associated with soil nutrient cycling. In summary, tobacco is a competitive plant in phytoremediation of BPA-contaminated soil, though the growth of tobacco could be inhibited at high concentration of BPA. Moreover, tobacco might promote the removal efficiency of BPA by regulating the rhizosphere bacteria communities.

High non-photochemical quenching of VPZ transgenic potato plants limits CO2 assimilation under high light conditions and reduces tuber yield under fluctuating light

Under natural conditions, photosynthesis has to be adjusted to fluctuating light intensities. Leaves exposed to high light dissipate excess light energy in form of heat at photosystem II (PSII) by a process called non-photochemical quenching (NPQ). Upon fast transition from light to shade, plants lose light energy by a relatively slow relaxation from photoprotection. Combined overexpression of violaxanthin de-epoxidase (VDE), PSII subunit S (PsbS) and zeaxanthin epoxidase (ZEP) in tobacco accelerates relaxation from photoprotection, and increases photosynthetic productivity. In Arabidopsis, expression of the same three genes (VPZ) resulted in a more rapid photoprotection but growth of the transgenic plants was impaired. Here we report on VPZ expressing potato plants grown under various light regimes. Similar to tobacco and Arabidopsis, induction and relaxation of NPQ was accelerated under all growth conditions tested, but did not cause an overall increased photosynthetic rate or growth of transgenic plants. Tuber yield of VPZ expressing plants was unaltered as compared to control plants under constant light conditions and even decreased under fluctuating light conditions. Under control conditions, levels of the phytohormone abscisic acid (ABA) were found to be elevated, indicating an increased violaxanthin availability in VPZ plants. However, the increased basal ABA levels did not improve drought tolerance of VPZ transgenic potato plants under greenhouse conditions. The failure to benefit from improved photoprotection is most likely caused by a reduced radiation use efficiency under high light conditions resulting from a too strong NPQ induction. Mitigating this negative effect in the future might help to improve photosynthetic performance in VPZ expressing potato plants.

PeVDE, a violaxanthin de-epoxidase gene from moso bamboo, confers photoprotection ability in transgenic Arabidopsis under high light

Plants employ an array of photoprotection mechanisms to alleviate the harmful effects of high light intensity. The violaxanthin cycle, which is associated with non-photochemical quenching (NPQ), involves violaxanthin de-epoxidase (VDE), and zeaxanthin epoxidase (ZEP) and is one of the most rapid and efficient mechanisms protecting plants under high light intensity. Woody bamboo is a class of economically and ecologically important evergreen grass species widely distributed in tropical and subtropical areas. However, the function of VDE in bamboo has not yet been elucidated. In this study, we found that high light intensity increased NPQ and stimulated the de-epoxidation of violaxanthin cycle components in moso bamboo (Phyllostachys edulis), whereas, samples treated with the VDE inhibitor (dithiothreitol) exhibited lower NPQ capacity, suggesting that violaxanthin cycle plays an important role in the photoprotection of bamboo. Further analysis showed that not only high light intensity but also extreme temperatures (4 and 42°C) and drought stress upregulated the expression of PeVDE in bamboo leaves, indicating that PeVDE is induced by multiple abiotic stresses. Overexpression of PeVDE under the control of the CaMV 35S promoter in Arabidopsis mutant npq1 mutant could rescue its NPQ, indicating that PeVDE functions in dissipating the excess absorbed light energy as thermal energy in bamboo. Moreover, compared with wild-type (Col-0) plants, the transgenic plants overexpressing PeVDE displayed enhanced photoprotection ability, higher NPQ capacity, slower decline in the maximum quantum yield of photosystem II (F _v /F _m ) under high light intensity, and faster recovery under optimal conditions. These results suggest that PeVDE positively regulates the response to high light intensity in bamboo plants growing in the natural environment, which could improve their photoprotection ability through the violaxanthin cycle and NPQ.

Tobacco-associated with Methylophilus sp. FP-6 enhances phytoremediation of benzophenone-3 through regulating soil microbial community, increasing photosynthetic capacity and maintaining redox homeostasis of plant

Benzophenone-3 (BP-3) has attracted widespread attention due to its large accumulation in the environment and its potential toxicity effects to human. This study aimed to investigate the effects of the combined application of tobacco and Methylophilus sp. strain FP-6 with both plant growth promoting (PGP) traits and BP-3 degradation function on BP-3 remediation in soil. The results showed that about 79.18% of BP-3 was removed from the soil after 30 days of plant culture inoculated with the FP-6 strain, which was significantly higher than the plant-alone treatment. Simultaneously, inoculation with strain FP-6 significantly improved growth performance, biomass production, antioxidant levels, osmoregulation substance, photosynthetic capacity and chlorophyll accumulation in tobacco. Moreover, the application of FP-6 shifted the bacterial community, and enhanced the abundance of BP-3-degrading or soil nutrient cycling-affecting bacteria (e.g., Chloroflexi, Bryobacter, MND1 and Myxococcales), which might be valuable for the promotion of plant growth and degradation of BP-3 in the soil. The results from this study gave first insights into the enhancement of BP-3 removal efficiency from soil by phytoremediation assisted with bacteria possessing both PGP properties and BP-3 degradation function. The role of soil bacterial community in this remediation process was also discussed.

Hormonal impact on photosynthesis and photoprotection in plants

Photosynthesis is not only essential for plants, but it also sustains life on Earth. Phytohormones play crucial roles in developmental processes, from organ initiation to senescence, due to their role as growth and developmental regulators, as well as their central role in the regulation of photosynthesis. Furthermore, phytohormones play a major role in photoprotection of the photosynthetic apparatus under stress conditions. Here, in addition to discussing our current knowledge on the role of the phytohormones auxin, cytokinins, gibberellins, and strigolactones in promoting photosynthesis, we will also highlight the role of abscisic acid beyond stomatal closure in modulating photosynthesis and photoprotection under various stress conditions through crosstalk with ethylene, salicylates, jasmonates, and brassinosteroids. Furthermore, the role of phytohormones in controlling the production and scavenging of photosynthesis-derived reactive oxygen species, the duration and extent of photo-oxidative stress and redox signaling under stress conditions will be discussed in detail. Hormones have a significant impact on the regulation of photosynthetic processes in plants under both optimal and stress conditions, with hormonal interactions, complementation, and crosstalk being important in the spatiotemporal and integrative regulation of photosynthetic processes during organ development at the whole-plant level.

Root NRT, NiR, AMT, GS, GOGAT and GDH expression levels reveal NO and ABA mediated drought tolerance in Brassica juncea L

Little is known about the interactive effects of exogenous nitric oxide (NO) and abscisic acid (ABA) on nitrogen (N) metabolism and related changes at molecular and biochemical levels under drought stress. The present study highlights the independent and combined effect of NO and ABA (grouped as "nitrate agonists") on expression profiles of representative key genes known to be involved in N-uptake and assimilation, together with proline metabolism, N-NO metabolism enzyme's activity and nutrient content in polyethylene glycol (PEG) treated roots of Indian mustard (B. juncea cv. Varuna). Here we report that PEG mediated drought stress negatively inhibited growth performance, as manifested by reduced biomass (fresh and dry weight) production. Total N content and other nitrogenous compounds (NO3-, NO2-) were decreased; however, NH4+, NH4+/ NO3- ratio and total free amino acids content were increased. These results were positively correlated with the PEG induced changes in expression of genes and enzymes involved in N-uptake and assimilation. Also, PEG supply lowered the content of macro- and micro-nutrients but proline level and the activity of ∆1-pyrroline-5-carboxylate synthetase increased indicating increased oxidative stress. However, all these responses were reversed upon the exogenous application of nitrate agonists (PEG + NO, PEG + NO + ABA, and PEG + ABA) where NO containing nitrate agonist treatment i.e. PEG + NO was significantly more effective than PEG + ABA in alleviating drought stress. Further, increases in activities of L-arginine dependent NOS-like enzyme and S-nitrosoglutathione reductase were observed under nitrate agonist treatments. This indicates that the balanced endogenous change in NO and ABA levels together during synthesis and degradation of NO mitigated the oxidative stress in Indian mustard seedlings. Overall, our results reveal that NO independently or together with ABA may contribute to improved crop growth and productivity under drought stress.

Photosynthetic activity and RAPD profile of polyethylene glycol treated B. juncea L. under nitric oxide and abscisic acid application

The involvement of two extremely important signalling molecules, nitric oxide (NO) and abscisic acid (ABA) has been employed by plants to facilitate the adaptive/tolerate response during stressful conditions. However, the interactive role of exogenously applied NO and ABA is very less studied at physiological, biochemical and molecular levels. The present study therefore, evaluated the effects of individual and simultaneous addition of exogenous NO donor SNP (100μM) and ABA (10μM) on photosynthesis, Calvin-Benson cycle enzymes, S-assimilation enzymes, oxidative stress components, and genotoxicity in Brassica juncea cv. Varuna, exposed to polyethylene glycol (PEG)-induced drought stress. Results showed that a loss induced by PEG was significantly surpassed by the application of NO or/and ABA with PEG for chlorophyll content, net photosynthestic rate (Pn), internal CO₂ concentration (Ci), stomatal conductance (gs), transpiration rate (Tr), maximum photosystem II (PSII) efficiency (Fv/Fm), actual PSII efficiency (ΦPSII), intrinsic PSII efficiency (Fv´/ Fm´), photochemical quenching (qP), non-photochemical quenching (NPQ), electron transport chain (ETC), ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo), glyceraldehyde-3-phosphate dehydrogenase (GapDH), phosphoribulokinase (PRK), ATP-sulfurylase (ATP-S), and serine acetyltransferase (SAT) activities. The genomic template stability (GTS) (measured as changes in RAPD profiles) was significantly affected and showed varying degrees of DNA polymorphism, highest in PEG and lowest in PEG + NO and PEG + NO + ABA. Furthermore, the changes in RAPD profiles showed consistent results when compared with various photosynthetic and oxidative parameters. Altogether, this study concluded that supplementation of individual NO and together with ABA was more effective than individual ABA in alleviating PEG-induced drought stress in B. juncea L. seedlings.

Salicylic acid application alleviates the adverse effects of triclosan stress in tobacco plants through the improvement of plant photosynthesis and enhancing antioxidant system

Triclosan (TCS) is a chlorophenol which is highly bacteriostatic and used in a wide array of consumer products. TCS is now one of the most commonly detected organic pollutants in the sewage sludges. The sludge utilization for fertilizers on agricultural land would pose the risk of causing adverse effects on plant growth and yield by TCS. However, the toxicity of TCS toward plants is comparatively less understood. In this study, we assessed the effects of TCS on tobacco plants which were grown in MS medium or soils containing various concentrations of TCS. Our results indicated that TCS at the concentration of 2 mg/L could strongly inhibit the tobacco seed germination. TCS could suppress tobacco plant growth in soil with different concentrations (10, 20, and 50 mg/kg) of TCS through the downregulation of chlorophyll contents, restricting photosynthesis and increasing generation of reactive oxygen species (ROS). Salicylic acid (SA) plays important roles in the stress response of plants. The role of exogenous SA application in protecting tobacco plants from TCS stress was also investigated in this study. SA application could significantly increase net photosynthesis, enhance antioxidant enzyme activity, and thereby enhancing tobacco plant tolerance to TCS. Moreover, the activation of MPK3 and MPK6 induced by TCS was downregulated in plants with the treatment of SA. It was thus referred that mitogen-activated protein kinases (MAPKs) might play a key role in the signal transduction of TCS stress, and this process might be regulated by SA signaling. Overall, our results demonstrated that TCS had negative impacts on tobacco plants and SA played a protective role on tobacco plants against TCS stress.

Nitric oxide and abscisic acid protects against PEG-induced drought stress differentially in Brassica genotypes by combining the role of stress modulators, markers and antioxidants

The present study was designed to see the effect of exogenous nitric oxide (NO) and abscisic acid (ABA) and their interaction on physiological and biochemical activities in leaves and roots of two Indian mustard (Brassica juncea) cultivars [cv. Pusa Jagannath (PJN) and Varuna (VAR)] exposed to polyethylene glycol (PEG)-induced drought stress. Seven days old hydroponically grown seedlings were treated with PEG (10%), sodium nitroprusside, a NO donor [NO (100 μM)] and abscisic acid [ABA (10 μM)], using different combinations as: Control, ABA, NO, PEG, PEG + ABA, PEG + NO, and PEG + NO + ABA. Results revealed that in response to PEG-induced drought stress leaf relative water content, chlorophyll, carotenoid and protein content decreased with increased production of O₂^-●, MDA, H₂O₂, cysteine content and non-enzymatic antioxidants (including proline, flavonoid, phenolic, anthocyanin, and ascorbic acid), whereas, the enzymatic antioxidants (including SOD, CAT, APX, GR) showed the response range from no effect to increase or decrease in certain enzymes in both Brassica cultivars. The application of NO or/and ABA in PEG-stressed cultivars showed that both enzymatic and non-enzymatic antioxidants responded differently to attenuate oxidative stress in leaves and roots of both cultivars. Overall, PJN had the antioxidant protection mainly through the accumulation of non-enzymatic antioxidants, whereas VAR showed tolerance by the enhancement of both enzymatic and non-enzymatic antioxidant activities. Altogether, the study concluded that the independent NO and its interaction with ABA (PEG + NO and PEG + NO + ABA) were much effective than independent ABA (PEG + ABA) in lowering PEG-drought stress in Brassica cultivars.

Overexpression of the ChVDE gene, encoding a violaxanthin de-epoxidase, improves tolerance to drought and salt stress in transgenic Arabidopsis

To investigate the protective mechanism of violaxanthin de-epoxidase (VDE) zeaxanthin in Cerasus humilis under drought and salt-stress conditions, we cloned the entire cDNA sequence of ChVDE from C. humilis and generated ChVDE-overexpression (OE) and ChVDE-complementation (CE) Arabidopsis plants. The open reading frame of ChVDE contained 1,446 bp nucleotides and encoded 481 amino acids. The ChVDE showed the highest similarity with those of Camellia sinensis and Citrus sinensis. Subcellular localization analysis showed that ChVDE was located in the chloroplasts. OE plants showed stronger root growth and higher levels of total chlorophyll as compared to WT and VDE mutant (npq1-2) plants. Moreover, the relative de-epoxidation state of the xanthophyll cycle pigments (A + Z)/(V + A+Z) was higher in OE plants than in the controls. OE plants had enhanced photosynthetic rates, respiration rates, and transpiration rates compared with the WT or npq1-2 plants after drought or salt treatment. Collectively, our results demonstrate that ChVDE plays a positive role in both drought and salt tolerance.

Wheat and rye genome confer specific phytohormone profile features and interplay under water stress in two phenotypes of triticale

The aim of the experiment was to determine phytohormone profile of triticale and quality-based relationships between the analyzed groups of phytohormones. The study involved two triticale phenotypes, a long-stemmed one and a semi-dwarf one with Dw1 gene, differing in mechanisms of acclimation to drought and controlled by wheat or rye genome. Water deficit in the leaves triggered a specific phytohormone response in both winter triticale phenotypes attributable to the dominance of wheat (semi-dwarf cultivar) or rye (long-stemmed cultivar) genome. Rye genome in long-stemmed triticale was responsible for specific increase (tillering: gibberellic acid; heading: N6-isopentenyladenine, trans-zeatin-9-riboside, cis-zeatin-9-riboside; flowering: N6-isopentenyladenine, indolebutyric acid, salicylic acid) or decrease (heading: trans-zeatin) in the content of some phytohormones. Wheat genome in semi-dwarf triticale controlled a specific increase in trans-zeatin content at heading and anthesis in gibberellin A1 during anthesis. The greatest number of changes in the phytohormone levels was observed in the generative phase. In both triticale types, the pool of investigated phytohormones was dominated by abscisic acid and gibberellins. The semi-dwarf cultivar with Dw1 gene was less sensitive to gibberellins and its mechanisms of acclimation to water stress were mainly ABA-dependent. An increase in ABA and gibberellins during drought and predominance of these hormones in the total pool of analyzed phytohormones indicated their equal share in drought acclimation mechanisms in long-stemmed cultivar.

Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress-induced response via the VTC2 gene encoding GDP-l-galactose phosphorylase

Ascorbate (vitamin C) plays essential roles in stress resistance, development, signaling, hormone biosynthesis and regulation of gene expression; however, little is known about its biosynthesis in algae. In order to provide experimental proof for the operation of the Smirnoff-Wheeler pathway described for higher plants and to gain more information on the regulation of ascorbate biosynthesis in Chlamydomonas reinhardtii, we targeted the VTC2 gene encoding GDP-l-galactose phosphorylase using artificial microRNAs. Ascorbate concentrations in VTC2 amiRNA lines were reduced to 10% showing that GDP-l-galactose phosphorylase plays a pivotal role in ascorbate biosynthesis. The VTC2 amiRNA lines also grow more slowly, have lower chlorophyll content, and are more susceptible to stress than the control strains. We also demonstrate that: expression of the VTC2 gene is rapidly induced by H₂ O₂ and ¹ O₂ resulting in a manifold increase in ascorbate content; in contrast to plants, there is no circadian regulation of ascorbate biosynthesis; photosynthesis is not required per se for ascorbate biosynthesis; and Chlamydomonas VTC2 lacks negative feedback regulation by ascorbate in the physiological concentration range. Our work demonstrates that ascorbate biosynthesis is also highly regulated in Chlamydomonas albeit via mechanisms distinct from those previously described in land plants.

Comparative transcriptome analysis highlights the crucial roles of photosynthetic system in drought stress adaptation in upland rice

Drought stress is one of the major adverse environmental factors reducing plant growth. With the aim to elucidate the underlying molecular basis of rice response to drought stress, comparative transcriptome analysis was conducted between drought susceptible rice cultivar Zhenshan97 and tolerant cultivar IRAT109 at the seedling stage. 436 genes showed differential expression and mainly enriched in the Gene Ontology (GO) terms of stress defence. A large number of variations exist between these two genotypes including 2564 high-quality insertion and deletions (INDELs) and 70,264 single nucleotide polymorphism (SNPs). 1041 orthologous gene pairs show the ratio of nonsynonymous nucleotide substitution rate to synonymous nucleotide substitutions rate (Ka/Ks) larger than 1.5, indicating the rapid adaptation to different environments during domestication. GO and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis of positive selection genes suggested that photosynthesis represents the most significant category. The collocation of positively selected genes with the QTLs of photosynthesis and the different photosynthesis performance of these two cultivars further illuminate the crucial function of photosynthesis in rice adaptation to drought stress. Our results also provide fruitful functional markers and candidate genes for future genetic research and improvement of drought tolerance in rice.

Current Understanding of the Interplay between Phytohormones and Photosynthesis under Environmental Stress

Abiotic stress accounts for huge crop losses every year across the globe. In plants, the photosynthetic machinery gets severely damaged at various levels due to adverse environmental conditions. Moreover, the reactive oxygen species (ROS) generated as a result of stress further promote the photosynthetic damage by inhibiting the repair system of photosystem II. Earlier studies have suggested that phytohormones are not only required for plant growth and development, but they also play a pivotal role in regulating plants’ responses to different abiotic stress conditions. Although, phytohormones have been studied in great detail in the past, their influence on the photosynthetic machinery under abiotic stress has not been studied. One of the major factors that limits researchers fromelucidating the precise roles of phytohormones is the highly complex nature of hormonal crosstalk in plants. Another factor that needs to be elucidated is the method used for assessing photosynthetic damage in plants that are subjected to abiotic stress. Here, we review the current understanding on the role of phytohormones in the photosynthetic machinery under various abiotic stress conditions and discuss the potential areas for further research.

Identification of QTLs with main, epistatic and QTL × environment interaction effects for salt tolerance in rice seedlings under different salinity conditions

Salt tolerance of rice (Oryza sativa L.) at the seedling stage is one of the major determinants of its stable establishment in saline soil. One population of recombinant inbred lines (RILs, F (2:9)) derived from a cross between the salt-tolerant variety Jiucaiqing and the salt-sensitive variety IR26 was used to determine the genetic mechanism of four salt tolerance indices, seedling height (SH), dry shoot weight (DSW), dry root weight (DRW) and Na/K ratios (Na/K) in roots after 10 days in three salt concentrations (0.0, 0.5 and 0.7 % NaCl). The main effect QTLs (M-QTLs) and epistatic QTLs (E-QTLs) were detected by QTL IciMapping program using single environment phenotypic values. Eleven M-QTLs and 11 E-QTLs were identified for the salt tolerance indices. There were six M-QTLs and two E-QTLs identified for SH, three M-QTLs and five E-QTLs identified for DSW, two M-QTLs and one E-QTL identified for DRW, and three E-QTLs identified for Na/K. The phenotypic variation explained by each M-QTL and E-QTL ranged from 7.8 to 23.9 % and 13.3 to 73.7 %, respectively. The QTL-by-environment interactions were detected by QTLNetwork program in the joint analyses of multi-environment phenotypic values. Six M-QTLs and five E-QTLs were identified. The phenotypic variation explained by each QTL and QTL × environment interaction ranged from 0.95 to 6.90 % and 0.02 to 0.50 %, respectively. By comparing chromosomal positions of these M-QTLs with those previously identified, five M-QTLs qSH1.3, qSH12.1, qSH12.2, qDSW12.1 and qDRW11 might represent novel salt tolerance genes. Five selected RILs with high salt tolerance had six to eight positive alleles of the M-QTLs, indicating that pyramiding by marker-assisted selection (MAS) of M-QTLs can be applied in rice salt tolerance breeding programs.