Abscisic Acid Production Research Articles

Red Light and the Dormancy-Germination Decision in Arabidopsis Seeds.

The Arabidopsis dormancy-germination transition is known to be environmentally cued and controlled by the competing hormones abscisic acid (ABA) and gibberellin (GA) produced by the seed. Recently, new molecular details have emerged concerning the propagation of red light through a complex gene regulatory network involving PhyB, PIF1, and RVE1. This network influences the formation of the PIF1-RVE1 complex [1,2]. The PIF1-RVE1 complex is a transcription factor that regulates the production of ABA and GA and helps shift the balance to high concentration of ABA and low concentration of GA, which corresponds to a dormant seed state. This newly discovered gene regulatory network has not been analyzed mathematically. Our analysis shows that this gene regulatory network exhibits switch-like bistability as a function of the red light input and makes a suite of biologically testable predictions concerning seed dormancy and germination in response to the amplitude and periodicity of an oscillatory red light input.

Plant growth-promoting properties of bacterial endophytes isolated from roots of Thymus vulgaris L. and investigate their role as biofertilizers to enhance the essential oil contents.

The main objective of the current study was to improve the essential oil contents of Thymus vulgaris L. using bio-inoculation with bacterial endophytes. Therefore, out of fourteen endophytic bacterial isolates obtained from roots of T. vulgaris, five isolates were selected based on the highest nitrogen-fixation and phosphate solubilization activity and identified as: Bacillus haynesii T9r, Citrobacter farmeri T10r, Bacillus licheniformis T11r, Bacillus velezensis T12r, and Bacillus velezensis T13r. These five strains have been recorded as ammonia, hydrogen cyanide (HCN), siderophores, and indole-3-acetic acid (IAA) producers. These strains have the efficacy to fix-nitrogen by reduction of acetylene with values of 82.133±1.4-346.6±1.4 n-mole-C2H4/ml/24 h. The IAA, gibberellic acid, abscisic acid, benzyl, kinten, and ziaten production were confirmed using HPLC. Two strains of T11r and T13r showed the highest plant growth-promoting properties and were selected for bio-inoculation of T. vulgaris individually or in a consortium with different mineral fertilization doses (0, 50, 75, and 100%) under field conditions. The highest growth performance was attained with the endophytic consortium (T11r+T13r) in the presence of 100% mineral fertilization. The GC-MS analysis of thyme oil contents showed the presence of 23 various compounds with varying percentages and the thymol fraction represented the highest percentages (39.1%) in the presence of the bacterial consortium.

Application of Chitosan in Plant Defense Responses to Biotic and Abiotic Stresses

Chitosan, a copolymer of N-acetyl-D-glucosamine and D-glucosamine, which possesses properties that make it useful in various fields, is produced by the deacetylation of chitin derivatives. It is used in agriculture as a biostimulant for plant growth and protection, it also induces several responsive genes, proteins, and secondary metabolites in plants. Chitosan elicits a signal transduction pathway and transduces secondary molecules such as hydrogen peroxide and nitric oxide. Under biotic stress, chitosan can stimulate phytoalexins, pathogenesis-related proteins, and proteinase inhibitors. Pretreatment of chitosan before exposure to abiotic stresses (drought, salt, and heat) induces plant growth, production of antioxidant enzymes, secondary metabolites, and abscisic acid (ABA). It also causes changes in physiology, biochemistry, and molecular biology of the plant cells. However, plant responses depend on different chitosan-based structures, concentrations, species, and developmental stages. This review collects updated information on chitosan applications, particularly in plant defense responses to biotic and abiotic stress conditions.

Plant Growth Alterations in Halophyte Prosopis strombulifera (Lam.) Benth. and Natrophile Glycine max (L.) Merril in Response to Salinity and Changes in Auxin Transport

The effects of changes in auxin transport in response to different osmotic potentials (Ψo) were analyzed in the roots and leaves of two leguminous species with different degrees of salt tolerance: the halophyte Prosopis strombulifera (Lam.) Benth. and the glycophyte Glycine max L. The potentials were generated with sodium chloride (NaCl), sodium sulfate (Na2SO4), and the iso-osmotic mixture of both salts (NaCl + Na2SO4). The values evaluated were −1, −1.8, and −2.6 MPa for P. strombulifera, and −0.47, −0.69, and −0.87 MPa for G. max. In addition, the plants were sprayed with 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor. The parameters measured included root length, shoot height, number of leaves, relative membrane permeability in roots, and endogenous levels of abscisic acid (ABA), indole-3-acetic acid (IAA), and zeatin (Z). Significant responses were observed at the lowest potentials evaluated (−2.6 MPa for P. strombulifera and −0.89 MPa for G. max). Treatment with Na2SO4 inhibited plant growth more than the others, increased the relative membrane permeability, and enhanced ABA production to its highest levels. These toxic effects were slightly reversed in the presence of iso-osmotic mixture. TIBA brought about impaired development in shoots and roots, the highest values for membrane permeability, alterations in the distribution of endogenous ABA, IAA, and Z, as well as harmful effects on the growth response of both species. In general, the alterations in auxin transport intensified the effects of salinity, which confirms the essential role of this mechanism in plants under salt stress or in normal, non-stressful conditions.

Cytokinin activity during early kernel development corresponds positively with yield potential and later stage ABA accumulation in field-grown wheat (Triticum aestivum L.).

Early cytokinin activity and late abscisic acid dynamics during wheat kernel development correspond to cultivars with higher yield potential. Cytokinins represent prime targets for marker development for wheat breeding programs. Two major phytohormone groups, abscisic acid (ABA) and cytokinins (CKs), are of crucial importance for seed development. Wheat (Triticum aestivum L.) yield is, to a high degree, determined during the milk and dough stages of kernel development. Therefore, understanding the hormonal regulation of these early growth stages is fundamental for crop-improvement programs of this important cereal. Here, we profiled ABA and 25 CK metabolites (including active forms, precursors and inactive conjugates) during kernel development in five field-grown wheat cultivars. The levels of ABA and profiles of CK forms varied greatly among the tested cultivars and kernel stages suggesting that several types of CK metabolites are involved in spatiotemporal regulation of kernel development. The seed yield potential was associated with the elevated levels of active CK levels (tZ, cZ). Interestingly, the increased kernel cZ levels were followed by higher ABA production, suggesting there is an interaction between these two phytohormones. Furthermore, we analyzed the expression patterns of representatives of the four main CK metabolic gene families. The unique transcriptional patterns of the IPT (biosynthesis) and ZOG (reversible inactivation) gene family members (GFMs) in the high and low yield cultivars additionally indicate that there is a significant association between CK metabolism and yield potential in wheat. Based on these results, we suggest that both CK metabolites and their associated genes, can serve as important, early markers of yield performance in modern wheat breeding programs.

Effect of experimental DNA demethylation on phytohormones production and palatability of a clonal plant after induction via jasmonic acid

Many plant species protect themselves against herbivores through mechanical or chemical so‐called inducible defences (ID). These are regulated via a hormonal cascade which may be under epigenetic control and in which jasmonic acid (JA) plays a prominent role. In this study, we indirectly tested the role of DNA methylation in the production of ID and the synthesis of hormones involved in the ID signalling cascade. Using different intensities of 5‐azacytidine application, we aimed to produce plants of Trifolium repens with different levels of DNA methylation alteration. We then elicited the plants together with controls, i.e. plants with natural DNA methylation status, with JA and then indirectly recorded ID production in herbivore‐choice trials in which the leaves of plants with different DNA methylation statuses were provided to caterpillars of a generalist herbivore, Spodoptera littoralis. We also analysed the balance of several key defence hormones such as jasmonates, abscisic acid (ABA), indole‐3‐acetic acid (IAA) and salicylic acid in the plants. We found that the S. littoralis preferred demethylated plants over non‐demethylated controls. Demethylation also reduced production of JA, ABA and IAA. We conclude that DNA methylation modulates expression of ID likely via regulation of signalling hormones involved in the establishment of defence.

Combined high leaf hydraulic safety and efficiency provides drought tolerance in Caragana species adapted to low mean annual precipitation

Summary Clarifying the coordination of leaf hydraulic traits with gas exchange across closely‐related species adapted to varying rainfall can provide insights into plant habitat distribution and drought adaptation.The leaf hydraulic conductance (K leaf), stomatal conductance (g s), net assimilation (A), vein embolism and abscisic acid (ABA) concentration during dehydration were quantified, as well as pressure–volume curve traits and vein anatomy in 10 Caragana species adapted to a range of mean annual precipitation (MAP) conditions and growing in a common garden.We found a positive correlation between Ψleaf at 50% loss of K leaf (K leaf P 50) and maximum K leaf (K leaf‐max) across species. Species from low‐MAP environments exhibited more negative K leaf P 50 and turgor loss point, and higher K leaf‐max and leaf‐specific capacity at full turgor, along with higher vein density and midrib xylem per leaf area, and a higher ratio of K leaf‐max : maximum g s. Tighter stomatal control mediated by higher ABA accumulation during dehydration in these species resulted in an increase in hydraulic safety and intrinsic water use efficiency (WUEi) during drought.Our results suggest that high hydraulic safety and efficiency combined with greater stomatal sensitivity triggered by ABA production and leading to greater WUEi provides drought tolerance in Caragana species adapted to low‐MAP environments.

Enhancement of Drought-Stress Tolerance of Brassica oleracea var. italica L. by Newly Isolated Variovorax sp. YNA59.

Drought is a major abiotic factor and has drastically reduced crop yield globally, thus damaging the agricultural industry. Drought stress decreases crop productivity by negatively affecting crop morphological, physiological, and biochemical factors. The use of drought tolerant bacteria improves agricultural productivity by counteracting the negative effects of drought stress on crops. In this study, we isolated bacteria from the rhizosphere of broccoli field located in Daehaw-myeon, Republic of Korea. Sixty bacterial isolates were screened for their growth-promoting capacity, in vitro abscisic acid (ABA), and sugar production activities. Among these, bacterial isolates YNA59 was selected based on their plant growth-promoting bacteria traits, ABA, and sugar production activities. Isolate YNA59 highly tolerated oxidative stress, including hydrogen peroxide (H2O2) and produces superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities in the culture broth. YNA59 treatment on broccoli significantly enhanced plant growth attributes, chlorophyll content, and moisture content under drought stress conditions. Under drought stress, the endogenous levels of ABA, jasmonic acid (JA), and salicylic acid (SA) increased; however, inoculation of YNA59 markedly reduced ABA (877 ± 22 ng/g) and JA (169.36 ± 20.74 ng/g) content, while it enhanced SA levels (176.55 ± 9.58 ng/g). Antioxidant analysis showed that the bacterial isolate YNA59 inoculated into broccoli plants contained significantly higher levels of SOD, CAT, and APX, with a decrease in GPX levels. The bacterial isolate YNA59 was therefore identified as Variovorax sp. YNA59. Our current findings suggest that newly isolated drought tolerant rhizospheric Variovorax sp. YNA59 is a useful stress-evading rhizobacterium that improved droughtstress tolerance of broccoli and could be used as a bio-fertilizer under drought conditions.

Effects of Exogenous Melatonin and ABA on Photosynthetic Characteristics of Naturally Aging Kiwi Seedlings

In this study, the annual yellow kiwi seedlings which were treated with 200μmol/L melatonin (MT), 15μmmol/L abscisic acid (ABA) and 5mmol/L sodium tungstate solution (STD) were used as experimental materials to study the changes in physiological indicators of kiwi fruit under natural aging. After comprehensive analysis, we can speculate that MT may affect the photosynthetic characteristics of aging kiwi by affecting ABA production and keeping its content at a moderate level. The experiment results provided theoretical basis and practical guidance for delaying the production and application of kiwi seedlings.

Effect of Ammonia and Indole-3-acetic Acid Producing Endophytic Klebsiella pneumoniae YNA12 as a Bio-Herbicide for Weed Inhibition: Special Reference with Evening Primroses.

Information on the use of endophytic bacteria as a bio-herbicide for the management of weed control in agricultural fields is limited. The current study aimed to isolate endophytic bacteria from evening primroses and to screen them for their bio-herbicidal activity. Two isolated endophytic bacteria (Pantoea dispersa YNA11 and Klebsiella pneumoniae YNA12) were initially screened for citrate utilization and for indole-3-acetic acid (IAA) and catalase production. The preliminary biochemical assessment showed YNA12 as a positive strain. Ammonia, catalase, and IAA in its culture filtrate were quantified. Gas Chromatography/Mass Spectroscopy- Selective Ion Monitoring (GC/MS-SIM) analysis revealed the production of IAA by YNA12 in a time-dependent manner. YNA12 also exhibited significant ammonia-producing potential and catalase activity against hydrogen peroxide. The YNA12 culture filtrate significantly inhibited the germination rate of evening primrose seeds, resulting in a marked reduction in seedling length and biomass compared with those of the control seeds. Moreover, the culture filtrate of YNA12 significantly accelerated the endogenous abscisic acid (ABA) production and catalase activity of evening primrose seedlings. Macronutrient regulation was adversely affected in the seedlings exposed to the culture filtrate of YNA12, leading to inhibition of seed germination. The current results suggest that endophytic YNA12 may be used as a potent bio-herbicidal agent for controlling weed growth and development.

Molybdenum Application Regulates Oxidative Stress Tolerance in Winter Wheat Under Different Nitrogen Sources

Molybdenum (Mo), an essential microelement, may enhance the oxidative stress tolerance in plants. However, the efficacy of Mo might be variable with different forms of nitrogen (N) fertilizer. The present study was conducted to investigate the role of Mo application in regulating oxidative stress tolerance in winter wheat under different N sources. A hydroponic study was carried out comprising of two winter wheat cultivars ‘97003’ and ‘97014’ as Mo efficient and Mo inefficient, respectively, under two Mo levels (0 and 1 μM) and three different N sources (NO3, NH4NO3, or NH4+). Winter wheat plants supplied with different N sources accumulated superoxide anions (O2−), and malonaldehyde (MDA) contents in the order of NH4+ > NO3 > NH4NO3, suggesting that sole application of either N sources, especially sole NH4+ source, may induce oxidative stress in winter wheat. However, Mo application decreased the MDA contents by 20.02%, 15.11%, and 25.89% in Mo-efficient cultivar and 30.75%, 23.79%, and 37.76% in Mo-inefficient cultivar under NO3, NH4NO3, and NH4+ sources, respectively, while increased antioxidant enzyme activities and carotenoids and abscisic acid (ABA) contents up-regulated the expressions of TaAO and TaAba3 genes. Mo application regulated oxidative stress tolerance in winter wheat under different N sources through enhancing ABA production and ROS-scavenging enzymes. Mo-efficient ‘97003’ winter wheat cultivar possesses a wider range of adaptability to withstand Mo-deficient conditions than Mo-inefficient ‘97014’ cultivar.

Metabolite/phytohormone-gene regulatory networks in soybean organs under dehydration conditions revealed by integration analysis.

SummaryMetabolites, phytohormones, and genes involved in dehydration responses/tolerance have been predicted in several plants. However, metabolite/phytohormone–gene regulatory networks in soybean organs under dehydration conditions remain unclear. Here, we analyzed the organ specificity of metabolites, phytohormones, and gene transcripts and revealed the characteristics of their regulatory networks in dehydration‐treated soybeans. Our metabolite/phytohormone analysis revealed the accumulation of raffinose, trehalose, and cis‐zeatin (cZ) specifically in dehydration‐treated roots. In dehydration‐treated soybeans, raffinose, and trehalose might have additional roles not directly involved in protecting the photosynthetic apparatus; cZ might contribute to root elongation for water uptake from the moisture region in soil. Our integration analysis of metabolites–genes indicated that galactinol, raffinose, and trehalose levels were correlated with transcript levels for key enzymes (galactinol synthase, raffinose synthase, trehalose 6‐phosphate synthase, trehalose 6‐phosphate phosphatase) at the level of individual plants but not at the organ level under dehydration. Genes encoding these key enzymes were expressed in mainly the aerial parts of dehydration‐treated soybeans. These results suggested that raffinose and trehalose are transported from aerial plant parts to the roots in dehydration‐treated soybeans. Our integration analysis of phytohormones–genes indicated that cZ and abscisic acid (ABA) levels were correlated with transcript levels for key enzymes (cytokinin nucleoside 5′‐monophosphate phosphoribohydrolase, cytokinin oxidases/dehydrogenases, 9‐cis‐epoxycarotenoid dioxygenase) at the level of individual plants but not at the organ level under dehydration conditions. Therefore, processes such as ABA and cZ transport, among others, are important for the organ specificity of ABA and cZ production under dehydration conditions.

Combined seed and foliar pre-treatments with exogenous methyl jasmonate and salicylic acid mitigate drought-induced stress in maize.

Susceptibility of plants to abiotic stresses, including extreme temperatures, salinity and drought, poses an increasing threat to crop productivity worldwide. Here the drought-induced response of maize was modulated by applications of methyl jasmonate (MeJA) and salicylic acid (SA) to seeds prior to sowing and to leaves prior to stress treatment. Pot experiments were conducted to ascertain the effects of exogenous applications of these hormones on maize growth, physiology and biochemistry under drought stress and well-watered (control) conditions. Maize plants were subjected to single as well as combined pre-treatments of MeJA and SA. Drought stress severely affected maize morphology and reduced relative water content, above and below-ground biomass, rates of photosynthesis, and protein content. The prolonged water deficit also led to increased relative membrane permeability and oxidative stress induced by the production of malondialdehyde (from lipid peroxidation), lipoxygenase activity (LOX) and the production of H2O2. The single applications of MeJA and SA were not found to be effective in maize for drought tolerance while the combined pre-treatments with exogenous MeJA+SA mitigated the adverse effects of drought-induced oxidative stress, as reflected in lower levels of lipid peroxidation, LOX activity and H2O2. The same pre-treatment also maintained adequate water status of the plants under drought stress by increasing osmolytes including proline, total carbohydrate content and total soluble sugars. Furthermore, exogenous applications of MeJA+SA approximately doubled the activities of the antioxidant enzymes catalase, peroxidase and superoxide dismutase. Pre-treatment with MeJA alone gave the highest increase in drought-induced production of endogenous abscisic acid (ABA). Pre-treatment with MeJA+SA partially prevented drought-induced oxidative stress by modulating levels of osmolytes and endogenous ABA, as well as the activities of antioxidant enzymes. Taken together, the results show that seed and foliar pre-treatments with exogenous MeJA and/or SA can have positive effects on the responses of maize seedlings to drought.

Wheat TabZIP8, 9, 13 participate in ABA biosynthesis in NaCl-stressed roots regulated by TaCDPK9-1

In plants, basic leucine zipper (bZIP) transcription factors (TFs) participate in various biological processes such as development and stress responses. But the molecular mechanism of wheat bZIP TFs modulating abscisic acid (ABA) biosynthesis is unknown. In this study, we demonstrated the expressions of three bZIP TF genes TabZIP8, 9, 13, were regulated by Triticum aestivum calcium (Ca2+)-dependent protein kinase 9–1 (TaCDPK9-1) and they took part in ABA biosynthesis in wheat roots under salt stress. We first isolated TabZIP8, 9, 13 and TaCDPK9-1 from wheat. TabZIP8, 9, 13 genes transcripts were strongly induced by salt stress, but salt-induced TabZIP8, 9, 13 transcriptions were drastically impaired by Ca2+ channel blocker LaCl3. TaCDPK9-1 kinase could interact with TabZIP8, 9, 13 TFs through yeast two-hybrid assay. Next, the expression levels of salt-induced wheat 9-cis-epoxycarotenoid dioxygenase1, 2 (TaNCED1,2) encoding a key enzyme controlling ABA production and salt-induced ABA content were found to be decreased under LaCl3 treatment, and yeast one-hybrid experiment revealed TabZIP8, 9, 13 could bind to the ABA-responsive elements (ABREs) and the promoter sequence of TaNCED2 gene. Together, our results suggest that salt stress-induced ABA accumulation is mediated by TabZIP8, 9, 13, which are adjusted by TaCDPK9-1 in wheat roots.

NO and ABA Interaction Regulates Tuber Dormancy and Sprouting in Potato.

In plants, nitric oxide synthase (NOS)-like or nitrate reductase (NR) produces nitric oxide (NO), which is involved in releasing seed dormancy. However, its mechanism of effect in potato remains unclear. In this study, spraying 40 μM sodium nitroprusside (SNP), an exogenous NO donor, quickly broke tuber dormancy and efficiently promoted tuber sprouting, whereas 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO), an NO scavenger, repressed the influence of NO on tuber sprouting. Compared with the control (distilled water), SNP treatment led to a rapid increase in NO content after 6 h and a decreased abscisic acid (ABA) content at 12 and 24 h. c-PTIO treatment significantly inhibited increase of NO levels and increased ABA production. In addition, NG-nitro-L-arginine methyl ester, an NOS inhibitor, clearly inhibited the NOS-like activity, whereas tungstate, an NR inhibitor, inhibited the NR activity. Furthermore, NO promoted the expression of a gene involved in ABA catabolism (StCYP707A1, encoding ABA 8′-hydroxylase) and inhibited the expression of a gene involved in ABA biosynthesis (StNCED1, encoding 9-cis-epoxycarotenoid dioxygenase), thereby decreasing the ABA content, disrupting the balance between ABA and gibberellin acid (GA), and ultimately inducing dormancy release and tuber sprouting. The results demonstrated that NOS-like or NR-generated NO controlled potato tuber dormancy release and sprouting via ABA metabolism and signaling in tuber buds.

Physiological and Molecular Responses of the Aboveground Part of Indica–Japonica Intersubspecific Tetraploid Rice Seedlings to Ion Beam Stress

Low-energy ion beam bombardment can induce various biological effects on plants, including stimulation, damage, and mutation. However, the physiological and molecular mechanisms of the biological effects of ion implantation are not fully understood. In this article, ion beam implantation was performed on Indica–Japonica intersubspecific tetraploid rice seeds to explore the responses of their seedlings. The investigation found that the aboveground part development of rice seedlings was inhibited, radiation damage was induced, and the metabolic accumulation and expression of abscisic acid (ABA) was disturbed by implantation with large doses of the low-energy $\text{N}^{+}$ beam. The activities of the antioxidant enzymes and proline (Pro) content were also increased by low-dose ion implantation induction. The malondialdehyde (MDA) content in seedlings under ion implantation was markedly higher than those of controls, and increased with the increase of ion beam irradiation doses. Transcriptional expression analysis of selected genes revealed that partly ABA anabolism genes associated with ABA production were significantly upregulated in seedlings in response to ion implantation. The aforementioned results will be useful for further research on the physiological and molecular mechanisms of Indica–Japonica intersubspecific tetraploid rice to ion beam stress.

Blue light postpones senescence of carnation flowers through regulation of ethylene and abscisic acid pathway-related genes

Endogenous signals in response to exogenous factors determine the senescence of flowers. Interactions among phytohormones especially abscisic acid (ABA) and ethylene are the major determinant of the senescence. In the present study, complex expression patterns of the genes related to ABA and ethylene as endogenous signals were investigated on cut carnations (Dianthus caryophyllus L.) that were exposed to different light spectra. Expression of ethylene biosynthetic (DcACS and DcACO), and signaling (DcETR and DcEin2) genes and also genes involved in ABA biosynthesis (DcZEP1 and DcNCED1), transport (DcABCG25 and DcABCG40) and catabolism (DcCYP707A1) were evaluated in petals of carnations exposed to three light spectra [white, blue and red]. Lowest relative membrane permeability (RMP) was detected in flowers that exposed to Blue light (BLFs), as a consequence, the longest vase life was found in BLFs. The Red and White lights markedly accelerated flower senescence and increased expression of DcACS and DcACO on day 6 and 10 of vase life assessment respectively; while Blue light inhibited the expression of ethylene biosynthetic genes. Expression of the genes involved in the production and transport of ABA and in signal transduction of ethylene was elevated during vase life of flowers irrespective of exposure to different light spectra. In conclusion, Blue light can be an effective environmental factor to extend the vase life of carnation flowers by delaying the petal senescence through down-regulation of ethylene biosynthetic genes and up-regulation of ABA biosynthetic genes.

Isolation of Trichoderma in the rhizosphere soil of Syringa oblata from Harbin and their biocontrol and growth promotion function

For the effective biocontrol of Syringa powdery mildew (Mircosphaera syringejaponicae) and to promote seedling growth, we identified 44 of the 181 Trichoderma isolates (T1-T181) isolated from the rhizosphere soil. Analysis identified 10 Trichoderma species, and T. pseudoharzianum T1 (TpseT1), T. afroharzianum T52 (TafrT52), and T. asperelloides T57 (TaspT57) were selected to make Trichoderma biofertilizer because of their fast growth and high spore production. Exposing Syringa oblata to Trichoderma biofertilizer showed that TafrT52 and TaspT57 could induce abscisic acid (ABA) production, and promote the shedding of diseased leaves and the generation of new leaves. Furthermore, TafrT52 increased the catalase (CAT) activity and reduced the H2O2 content. And the disease incidence was reduced by 37.84 % by Tasp (highest) in 2017 year and by 13.84 % by TpseT1(lowest) in 2018 year. In addition, all Trichoderma strains we selected could promote the lateral root growth of S. oblata seedlings; however, because of the downregulated gene expression at the late stage of chlorophyll synthesis, the chlorophyll content decreased in the new leaves. Antagonism among different Trichoderma species led to low biocontrol and growth promotion effects, thus the Trichoderma mixture cannot be use as biofertilizer. TafrT52, with better biocontrol and growth promotion effects, could be used for biocontrol of M. syringejaponicae.

MAPK-like protein 1 positively regulates maize seedling drought sensitivity by suppressing ABA biosynthesis.

Mitogen-activated protein kinase (MAPK) cascades play vital roles in regulating plant growth, development, and stress responses. MAPK-like (MPKL) proteins are a group of kinases containing the MAPK signature TxY motif and showing sequence similarity to MAPKs. However, the functions of plant MPKL proteins are currently unknown. The maize (Zea mays) genome contains four genes encoding MPKL proteins, here named ZmMPKL1 to ZmMPKL4. In this study, we show that ZmMPKL1 possesses kinase activity and that drought-induced ZmMPKL1 expression, ZmMPKL1 overexpression and knockout maize seedlings exhibited no visible morphological difference from wild-type B73 seedlings when grown under normal conditions. By contrast, under drought conditions, ZmMPKL1-overexpressing seedlings showed increased stomatal aperture, water loss, and leaf wilting and knockout seedlings showed the opposite phenotypes. Moreover, these drought-sensitive phenotypes in ZmMPKL1-overexpressing seedlings were restored by exogenous abscisic acid (ABA). ZmMPKL1 overexpression reduced drought-induced ABA production in seedlings and the knockout showed enhanced ABA production. Drought-induced transcription of ABA biosynthetic genes were suppressed and ABA catabolic genes were enhanced in ZmMPKL1-overexpressing seedlings, while their transcription were reversely regulated in knockout seedlings. These results suggest that ZmMPKL1 positively regulates seedlings drought sensitivity by altering the transcription of ABA biosynthetic and catabolic genes, and ABA homeostasis.

Production and roles of IAA and ABA during development of superior and inferior rice grains.

Current understanding of the role of plant hormones during cereal grain filling is confounded by contradictory reports on hormone production that is based on poor methodology. We report here on the accurate measurement of indole-3-acetic acid (IAA) and abscisic acid (ABA) by combined liquid chromatography-tandem mass spectrometry in multiple reaction-monitoring mode with heavy isotope labelled internal standards. ABA and IAA contents of superior versus inferior rice grains (ABA maxima 159 ng g-1 FW and 109 ng g-1 FW, IAA maxima 2 µg g-1 FW and 1.7 µg g-1 FW respectively) correlated with the expression of biosynthetic genes and with grain fill. Results confirm that grain ABA is produced primarily by OsNCED2(5), but suggest that ABA import and metabolism also play important roles in ABA regulation. The IAA content of grains is primarily influenced by OsYUC9 and OsYUC11. However, the distinct expression profile of OsYUC12 suggests a specific role for IAA produced by this enzyme. Co-expression of OsYUC12 with OsIAA29 indicates their involvement in a common signalling pathway. Co-expression and cis-element analysis identified several aleurone-specific transcriptional regulators as well as glutelin as strong candidates for detailed investigation for direct regulation by the auxin-signalling pathway.