Crassulacean acid metabolism in the Basellaceae (Caryophyllales)

• C₄ and crassulacean acid metabolism (CAM) have evolved in the order Caryophyllales many times but neither C₄ nor CAM have been recorded for the Basellaceae, a small family in the CAM‐rich sub‐order Portulacineae.
• 24 h gas exchange and day–night changes in titratable acidity were measured in leaves of Anredera baselloides exposed to wet–dry–wet cycles.
• While net CO₂ uptake was restricted to the light period in well‐watered plants, net CO₂ fixation in the dark, accompanied by significant nocturnal increases in leaf acidity, developed in droughted plants. Plants reverted to solely C₃ photosynthesis upon rewatering.
• The reversible induction of nocturnal net CO₂ uptake by drought stress indicates that this species is able to exhibit CAM in a facultative manner. This is the first report of CAM in a member of the Basellaceae.

     

Effect of localized reduction of gibberellins in different tobacco organs on drought stress tolerance and recovery

Drought resistance is increased in plants by the absence of the hormone gibberellic acid (GA) or by a lack of GA sensitivity. We studied the effects of tissue-specific reduction in GA levels on drought tolerance, on recovery from drought stress, and on primary and secondary growth using transgenic tobacco plants expressing the GA-inactivating gene PtGA2ox ₁ (GA 2-oxidase) specifically in leaves, stems, or roots. Localized reduction of bioactive GA₁ levels was achieved by tissue-specific expression of the PtGA2ox ₁ gene in leaves using the rbcs promoter (LD plants), in roots using the TobRB7 promoter (RD plants), and in stems using the LMX5 promoter (SD plants). In response to drought stress, all transgenic tobacco plants exhibited reduced primary and secondary growth and increased drought tolerance with a corresponding reduction in malondialdehyde levels, higher relative water content, increased proline and sugar content, and elevated peroxidase, superoxide dismutase, and catalase activities relative to wild-type plants. The highest level of drought tolerance and the most rapid recovery from stress was achieved by localized reduction of GA₁ in the roots of the RD transgenic plants. In addition, although the total bioactive GA₁ content in RD and LD plants was essentially identical, the heights of LD plants were significantly greater and drought tolerance was significantly less than in RD plants. It is possible that the site of gibberellin-related gene expression plays an important role in the balance between growth and drought tolerance.     

Drought‐inducible changes in the histone modification H3K9ac are associated with drought‐responsive gene expression in Brachypodium distachyon

• H3K9ac, an epigenetic marker, is widely distributed in plant genomes. H3K9ac enhances gene expression, which is highly conserved in eukaryotes. However, genome‐wide studies of H3K9ac in monocot species are limited, and the changes in H3K9ac under drought stress for individual genes are still not clear.
• We analysed changes in the H3K9ac level of Brachypodium distachyon under 20% PEG‐6000‐simulated drought stress conditions. We also performed chromatin immunoprecipitation, followed by next generation sequencing (ChIP‐seq) on H3K9ac to reveal changes in H3K9ac for individual genes at the genome‐wide level.
• Our study showed that H3K9ac was mainly enriched in gene exon regions. Drought increased or decreased the H3K9ac level at specific genomic loci. We identified 40 genes associated with increased H3K9ac levels and 36 genes associated with decreased H3K9ac levels under drought stress. Further, RT‐qPCR analyses showed that H3K9ac was positively associated with gene expression of those drought‐responsive genes.
• We conclude that H3K9ac enhances the expression level of a large number of drought‐responsive genes under drought stress in B. distachyon. The data presented here will help to reveal the correlation of some specific drought‐responsive genes and their enriched H3K9ac levels in the model plant B. distachyon.

     

OsASR5 enhances drought tolerance through a stomatal closure pathway associated with ABA and H2O2 signalling in rice

Drought is one of the major abiotic stresses that directly implicate plant growth and crop productivity. Although many genes in response to drought stress have been identified, genetic improvement to drought resistance especially in food crops is showing relatively slow progress worldwide. Here, we reported the isolation of abscisic acid, stress and ripening (ASR) genes from upland rice variety, IRAT109 (Oryza sativa L. ssp. japonica), and demonstrated that overexpression of OsASR5 enhanced osmotic tolerance in Escherichia coli and drought tolerance in Arabidopsis and rice by regulating leaf water status under drought stress conditions. Moreover, overexpression of OsASR5 in rice increased endogenous ABA level and showed hypersensitive to exogenous ABA treatment at both germination and postgermination stages. The production of H₂O₂, a second messenger for the induction of stomatal closure in response to ABA, was activated in overexpression plants under drought stress conditions, consequently, increased stomatal closure and decreased stomatal conductance. In contrast, the loss‐of‐function mutant, osasr5, showed sensitivity to drought stress with lower relative water content under drought stress conditions. Further studies demonstrated that OsASR5 functioned as chaperone‐like protein and interacted with stress‐related HSP40 and 2OG‐Fe (II) oxygenase domain containing proteins in yeast and plants. Taken together, we suggest that OsASR5 plays multiple roles in response to drought stress by regulating ABA biosynthesis, promoting stomatal closure, as well as acting as chaperone‐like protein that possibly prevents drought stress‐related proteins from inactivation.     

Expression of Arabidopsis Bax Inhibitor‐1 in transgenic sugarcane confers drought tolerance

The sustainability of global crop production is critically dependent on improving tolerance of crop plants to various types of environmental stress. Thus, identification of genes that confer stress tolerance in crops has become a top priority especially in view of expected changes in global climatic patterns. Drought stress is one of the abiotic stresses that can result in dramatic loss of crop productivity. In this work, we show that transgenic expression of a highly conserved cell death suppressor, Bax Inhibitor‐1 from Arabidopsis thaliana (AtBI‐1), can confer increased tolerance of sugarcane plants to long‐term (>20 days) water stress conditions. This robust trait is correlated with an increased tolerance of the transgenic sugarcane plants, especially in the roots, to induction of endoplasmic reticulum (ER) stress by the protein glycosylation inhibitor tunicamycin. Our findings suggest that suppression of ER stress in C₄ grasses, which include important crops such as sorghum and maize, can be an effective means of conferring improved tolerance to long‐term water deficit. This result could potentially lead to improved resilience and yield of major crops in the world.     

PeCHYR1, a ubiquitin E3 ligase from Populus euphratica,enhances drought tolerance via ABA‐induced stomatal closure by ROS production in Populus

Drought, a primary abiotic stress, seriously affects plant growth and productivity. Stomata play a vital role in regulating gas exchange and drought adaptation. However, limited knowledge exists of the molecular mechanisms underlying stomatal movement in trees. Here, PeCHYR1, a ubiquitin E3 ligase, was isolated from Populus euphratica, a model of stress adaptation in forest trees. PeCHYR1 was preferentially expressed in young leaves and was significantly induced by ABA (abscisic acid) and dehydration treatments. To study the potential biological functions of PeCHYR1, transgenic poplar 84K (Populus alba × Populus glandulosa) plants overexpressing PeCHYR1 were generated. PeCHYR1 overexpression significantly enhanced H₂O₂ production and reduced stomatal aperture. Transgenic lines exhibited increased sensitivity to exogenous ABA and greater drought tolerance than that of WT (wild‐type) controls. Moreover, up‐regulation of PeCHYR1 promoted stomatal closure and decreased transpiration, resulting in strongly elevated WUE (water use efficiency). When exposed to drought stress, transgenic poplar maintained higher photosynthetic activity and biomass accumulation. Taken together, these results suggest that PeCHYR1 plays a crucial role in enhancing drought tolerance via ABA‐induced stomatal closure caused by hydrogen peroxide (H₂O₂) production in transgenic poplar plants.     

Overexpression of ubiquitin‐like LpHUB1 gene confers drought tolerance in perennial ryegrass

HUB1, also known as Ubl5, is a member of the subfamily of ubiquitin‐like post‐translational modifiers. HUB1 exerts its role by conjugating with protein targets. The function of this protein has not been studied in plants. A HUB1 gene, LpHUB1, was identified from serial analysis of gene expression data and cloned from perennial ryegrass. The expression of this gene was reported previously to be elevated in pastures during the summer and by drought stress in climate‐controlled growth chambers. Here, pasture‐type and turf‐type transgenic perennial ryegrass plants overexpressing LpHUB1 showed improved drought tolerance, as evidenced by improved turf quality, maintenance of turgor and increased growth. Additional analyses revealed that the transgenic plants generally displayed higher relative water content, leaf water potential, and chlorophyll content and increased photosynthetic rate when subjected to drought stress. These results suggest HUB1 may play an important role in the tolerance of perennial ryegrass to abiotic stresses.     

Expression of an Arabidopsis molybdenum cofactor sulphurase gene in soybean enhances drought tolerance and increases yield under field conditions

LOS5/ABA3 gene encoding molybdenum cofactor sulphurase is involved in aldehyde oxidase (AO) activity in Arabidopsis, which indirectly regulates ABA biosynthesis and increased stress tolerance. Here, we used a constitutive super promoter to drive LOS5/ABA3 overexpression in soybean (Glycine max L.) to enhance drought tolerance in growth chamber and field conditions. Expression of LOS5/ABA3 was up‐regulated by drought stress, which led to increasing AO activity and then a notable increase in ABA accumulation. Transgenic soybean under drought stress had reduced water loss by decreased stomatal aperture size and transpiration rate, which alleviated leaf wilting and maintained higher relative water content. Exposed to drought stress, transgenic soybean exhibited reduced cell membrane damage by reducing electrolyte leakage and production of malondialdehyde and promoting proline accumulation and antioxidant enzyme activities. Also, overexpression of LOS5/ABA3 enhanced expression of stress‐up‐regulated genes. Furthermore, the seed yield of transgenic plants is at least 21% higher than that of wide‐type plants under drought stress conditions in the field. These data suggest that overexpression of LOS5/ABA3 could improve drought tolerance in transgenic soybean via enhanced ABA accumulation, which could activate expression of stress‐up‐regulated genes and cause a series of physiological and biochemical resistant responses.     

Tolerance to multiple climate stressors: a case study of Douglas‐fir drought and cold hardiness

相似文献   

Overexpression of SoACLA-1 Gene Confers Drought Tolerance Improvement in Sugarcane

Drought is one of the most severe stresses which limit sugarcane production in China. ATP citrate lyase (ACL) is a major enzyme responsible for the production of acetyl-CoA in cytoplasm and plays an important role in plant metabolism and stress response. In this study, sugarcane ACL gene SoACLA-1 was cloned. The plant overexpression vector of SoACLA-1 was built and transformed into sugarcane calli by Agrobacterium-mediated transformation, and PCR analysis confirmed that SoACLA-1 gene had been stably present in the T0, T1, and T2 generations of the transgenic sugarcane. In order to evaluate the drought resistance of the transgenic lines and verify the function of SoACLA-1 gene in the transgenic sugarcane, T1 generation of the SoACLA-1 transgenic sugarcane lines was used as the material to investigate the physiological and biochemical characteristics at 0 day, 3 days, 6 days, and 9 days after water stress and rewatering for 3 days. Comprehensive evaluation of four indicators (chlorophyll, malondialdehyde, proline, soluble sugar) related to drought resistance was done with membership fuzzy function method. The results showed that the drought resistance of five transgenic sugarcane lines from strong to weak, in turn, was RT2?>?RT4?>?RT3?>?RT1?>?WT, and the recovery ability after drought, in turn, was RT1?>?RT2?>?RT4?>?RT3?>?WT. The T2 generation of the SoACLA-1 transgenic sugarcane lines was used to analyze the physiological and biochemical changes and the expression of drought-related genes under water stress. The results showed that the transgenic sugarcane lines were more tolerant to drought as compared with the wild-type plants. Our findings indicated that SoACLA-1 gene plays an important role as a positive factor in response to water stress, and overexpression of SoACLA-1 can enhance drought tolerance in transgenic sugarcane plants.

     

Plant‐mediated effects of drought on aphid population structure and parasitoid attack

The effects of predicted climate change on aphid–natural enemy interactions have principally considered the effects of elevated carbon dioxide concentration and air temperature. However, increased incidence of summer droughts are also predicted in Northern Europe, which could affect aphid–plant interactions and aphid antagonists. We investigated how simulated summer drought affected the bird cherry–oat aphid, Rhopalosiphum padi L., and its natural enemy the parasitoid wasp Aphidius ervi. Drought and, to a greater extent, aphids reduced barley ( Hordeum vulgare) dry mass by 33% and 39%, respectively. Drought reduced leaf and root nitrogen concentrations by 13% and 28%, respectively, but foliar amino acid concentrations and composition remained similar. Aphid numbers were unaffected by drought, but population demography changed significantly; adults constituted 41% of the population on drought‐treated plants, but only 26% on those receiving ambient irrigation. Nymphs constituted 56% and 69% of the population on these plants, respectively, suggesting altered aphid development rates on drought‐stressed plants. Parasitism rates were significantly lower on drought‐stressed plants (9 attacks h^?1 compared with 35 attacks h^?1 on ambient‐irrigated plants), most likely because of lower incidence of nymphs and more adults, the latter being more difficult to parasitize. Any physiological changes in individual aphids did not affect parasitoid preferences, suggesting that attacks were postponed because of drought‐induced changes in aphid demography. This study demonstrates the potential for sporadic climate change events, such as summer drought, to be disruptive to herbivore–antagonist interactions.     

The oxalyl‐CoA synthetase‐regulated oxalate and its distinct effects on resistance to bacterial blight and aluminium toxicity in rice

• Oxalic acid is widely distributed in biological systems and known to play functional roles in plants. The gene AAE3 was recently identified to encode an oxalyl‐CoA synthetase (OCS) in Arabidopsis that catalyses the conversion of oxalate and CoA into oxalyl‐CoA. It will be particularly important to characterise the homologous gene in rice since rice is not only a monocotyledonous model plant, but also a staple food crop.
• Various enzymatic and biological methods have been used to characterise the homologous gene.
• We first defined that AAE3 in the rice genome (OsAAE3) also encodes an OCS enzyme. Its K_m for oxalate is 1.73 ± 0.12 mm , and V_m is 6824.9 ± 410.29 U·min^?1·mg protein^?1. Chemical modification and site‐directed mutagenesis analyses identified thiols as the active site residues for rice OCS catalysis, suggesting that the enzyme might be regulated by redox state. Subcellular localisation assay showed that the enzyme is located in the cytosol and predominantly distributed in leaf epidermal cells. As expected, oxalate levels increased when OCS was suppressed in RNAi transgenic plants. More interestingly, OCS‐suppressed plants were more susceptible to bacterial blight but more resistant to Al toxicity.
• The results demonstrate that the OsAAE3‐encoded protein also acts as an OCS in rice, and may play different roles in coping with stresses. These molecular, enzymatic and functional data provide first‐hand information to further clarify the function and mechanism of OCS in rice plants.