Phytohormone Homeostasis Research Articles

Extensive cross-talk among stress-regulated protective metabolites, biogenic-amines and phytohormone-signalling, co-ordinated by dopamine-mediated seed-priming, governs tolerance against fluoride stress in rice.

Seed priming with dopamine reduced fluoride bioaccumulation, induced endogenous dopamine level, thereby orchestrating phytohormone homeostasis and biogenic amine metabolism, and modulating osmolyte and antioxidant machinery to enhance fluoride tolerance in rice. The aim of this study was to decipher the efficacy of seed priming with dopamine in curtailing the adverse impacts of fluoride toxicity in rice seedlings. Fluoride-stressed seedlings exhibited severe growth retardation, high fluoride bioaccumulation, electrolyte leakage and marked cellular injuries. Dopamine priming stimulated the overall physiological growth parameters during stress, via reduced formation of H2O2, malondialdehyde and methylglyoxal, due to lesser fluoride-accumulation. Fluoride stress-induced endogenous dopamine level was further induced upon dopamine priming, marked by the up regulated DOPA decarboxylase expression. Additionally, dopamine treatment led to escalated activity of catalase, superoxide dismutase and glutathione peroxidase in the stressed seedlings, concomitant with altered CAT, SOD and GPX expression. The higher accumulation of protective osmolytes (proline and total amino acids) and non-enzymatic antioxidants (phenolics, flavonoids, anthocyanins, glutathione and carotenoids), upon dopamine priming, during fluoride stress, could be linked with the altered expression pattern of the respective genes. Dopamine promoted active utilization of the biogenic amine (polyamines and ϒ-amino butyric acid) pools for toxicity mitigation, correlated with the modulation of the concerned enzyme activity and gene expression. Dopamine stimulated the accumulation of phytohormones like gibberellin and salicylic acid, via inducing the biosynthetic genes like gibberellin-3-oxidase (GA3ox) and isochorismate synthase (ICS), respectively, while depreciating the abscisic acid and melatonin level during fluoride stress. To our knowledge, this is the first documented report for the remedial role of dopamine priming against fluoride stress in any plant species. This study will open new arenas in sustainable agriculture for the exploitation of this pulsating biomolecule against fluoride stress.

Cross-inoculation of rhizobiome from a congeneric ruderal plant imparts drought tolerance in maize (Zea mays) through changes in root morphology and proteome.

SUMMARYRhizobiome confer stress tolerance to ruderal plants, yet their ability to alleviate stress in crops is widely debated, and the associated mechanisms are poorly understood. We monitored the drought tolerance of maize (Zea mays) as influenced by the cross‐inoculation of rhizobiota from a congeneric ruderal grass Andropogon virginicus (andropogon‐inoculum), and rhizobiota from organic farm maintained under mesic condition (organic‐inoculum). Across drought treatments (40% field capacity), maize that received andropogon‐inoculum produced two‐fold greater biomass. This drought tolerance translated to a similar leaf metabolomic composition as that of the well‐watered control (80% field capacity) and reduced oxidative damage, despite a lower activity of antioxidant enzymes. At a morphological‐level, drought tolerance was associated with an increase in specific root length and surface area facilitated by the homeostasis of phytohormones promoting root branching. At a proteome‐level, the drought tolerance was associated with upregulation of proteins related to glutathione metabolism and endoplasmic reticulum‐associated degradation process. Fungal taxa belonging to Ascomycota, Mortierellomycota, Archaeorhizomycetes, Dothideomycetes, and Agaricomycetes in andropogon‐inoculum were identified as potential indicators of drought tolerance. Our study provides a mechanistic understanding of the rhizobiome‐facilitated drought tolerance and demonstrates a better path to utilize plant–rhizobiome associations to enhance drought tolerance in crops.

Involvement of ethylene in glutamate-mediated tomato fruit resistance to Alternaria alternata

Recent progress showed the potential of glutamate to regulate stress responses by affecting phytohormones homeostasis, but much remains to be explored. To decipher the role of ethylene in glutamate-induced resistance to Alternaria alternata, ethephon application, ethylene perception inhibitor (1-MCP) experiment and ethylene measurement were pursued. Concurrently, temporal alteration in ethylene biosynthesis and signaling pathways were transcriptionally analyzed in tomato fruit. Our data exhibited that ethylene conferred tomato fruit susceptibility rather than resistance to Alternaria alternata. The enhanced resistance in glutamate treatment was related to decreased ethylene production during the early stages of interaction, accompanied by lower expression levels of SlACS1, SlACS2 and SlACO1 relative to the control. Interestingly, 1-MCP induced amounts of resistance similar to that observed in glutamate treatment, while ethylene receptors (SlETR3 and SlETR4), mitogen-activated protein kinase SlMPK3 and ethylene response factor SlERF1 were down-regulated by glutamate during infection. Collectively, antagonizing the ethylene biosynthesis or signaling might play a pivotal role in glutamate-induced resistance to the necrotrophic pathogen Alternaria alternata.

Crucial Cell Signaling Compounds Crosstalk and Integrative Multi-Omics Techniques for Salinity Stress Tolerance in Plants.

In the era of rapid climate change, abiotic stresses are the primary cause for yield gap in major agricultural crops. Among them, salinity is considered a calamitous stress due to its global distribution and consequences. Salinity affects plant processes and growth by imposing osmotic stress and destroys ionic and redox signaling. It also affects phytohormone homeostasis, which leads to oxidative stress and eventually imbalances metabolic activity. In this situation, signaling compound crosstalk such as gasotransmitters [nitric oxide (NO), hydrogen sulfide (H2S), hydrogen peroxide (H2O2), calcium (Ca), reactive oxygen species (ROS)] and plant growth regulators (auxin, ethylene, abscisic acid, and salicylic acid) have a decisive role in regulating plant stress signaling and administer unfavorable circumstances including salinity stress. Moreover, recent significant progress in omics techniques (transcriptomics, genomics, proteomics, and metabolomics) have helped to reinforce the deep understanding of molecular insight in multiple stress tolerance. Currently, there is very little information on gasotransmitters and plant growth regulator crosstalk and inadequacy of information regarding the integration of multi-omics technology during salinity stress. Therefore, there is an urgent need to understand the crucial cell signaling crosstalk mechanisms and integrative multi-omics techniques to provide a more direct approach for salinity stress tolerance. To address the above-mentioned words, this review covers the common mechanisms of signaling compounds and role of different signaling crosstalk under salinity stress tolerance. Thereafter, we mention the integration of different omics technology and compile recent information with respect to salinity stress tolerance.

Explicating the cross-talks between nanoparticles, signaling pathways and nutrient homeostasis during environmental stresses and xenobiotic toxicity for sustainable cultivation of cereals

Precision farming using nanoparticles is a cutting-edge technology for safe cultivation of crop plants in marginal areas afflicted with environmental/climatic stresses like salinity, drought, extremes of temperature, ultraviolet B stress or polluted with xenobiotics like toxic heavy metals and fluoride. Major cereal crops like rice, wheat, maize, barley, sorghum and millets which provide the staple food for the entire global population are mainly glycophytes and are extremely susceptible to abiotic stress-induced oxidative injuries. Nanofertilization/exogenous spraying of beneficial nanoparticles alleviates the oxidative damages in cereals by altering the homeostasis of phytohormones like abscisic acid, gibberellins, cytokinins, auxins, salicylic acid, jasmonic acid and melatonin and by triggering the synthesis of gasotransmitter nitric oxide. Signaling cross-talks of nanoparticles with plant growth regulators enable activation of the defence machinery, comprising of antioxidants, thiol-rich compounds and glyoxalases and restrict xenobiotic mobilization by suppressing the expression of associated transporters. Accelerated nutrient uptake and grain biofortification under the influence of nanoparticles result in optimum crop productivity under sub-optimal conditions. However, over-dosing of even beneficial nanoparticles promotes severe phytotoxicity. Hence, the concentration of nanoparticles and mode of administering need to be thoroughly standardized before large-scale field applications, to ensure sustainable cereal cultivation with minimum ecological imbalance.

An NADPH oxidase regulates carbon metabolism and the cell cycle during root nodule symbiosis in common bean (Phaseolus vulgaris)

BackgroundRhizobium–legume symbiosis is a specific, coordinated interaction that results in the formation of a root nodule, where biological nitrogen fixation occurs. NADPH oxidases, or Respiratory Burst Oxidase Homologs (RBOHs) in plants, are enzymes that generate superoxide (O2•−). Superoxide produces other reactive oxygen species (ROS); these ROS regulate different stages of mutualistic interactions. For example, changes in ROS levels are thought to induce ROS scavenging, cell wall remodeling, and changes in phytohormone homeostasis during symbiotic interactions. In common bean (Phaseolus vulgaris), PvRbohB plays a key role in the early stages of nodulation.ResultsIn this study, to explore the role of PvRbohB in root nodule symbiosis, we analyzed transcriptomic data from the roots of common bean under control conditions (transgenic roots without construction) and roots with downregulated expression of PvRbohB (by RNA interference) non-inoculated and inoculated with R. tropici. Our results suggest that ROS produced by PvRBOHB play a central role in infection thread formation and nodule organogenesis through crosstalk with flavonoids, carbon metabolism, cell cycle regulation, and the plant hormones auxin and cytokinin during the early stages of this process.ConclusionsOur findings provide important insight into the multiple roles of ROS in regulating rhizobia–legume symbiosis.

Characterizing the impact of high temperature during grain filling on phytohormone levels, enzyme activity and metabolic profiles of an early indica rice variety.

Global warming results in high temperature stress (HTS), which presents severe challenges worldwide for modern agricultural production and will have significant impacts on the yield and quality of crops. Accumulation of photosynthetic products, activity of enzymes involved in sucrose-starch metabolism, phytohormone levels and metabolic profiling using LC-MS were analysed in the flag leaves and/or developing grains subjected to HTS during the grain-filling stage of an indica rice. HTS induced significant yield loss and reduced the grain quality, with lower amylose content. HTS reduced photosynthetic product accumulation in flag leaves and reduced starch accumulation in developing grains, compared to growth under normal temperatures. The activity of enzymes related to sucrose-starch metabolism were dis-regulated in developing grains grown under high temperature (HT). Moreover, phytohormone homeostasis in flag leaves and developing grains was also dramatically disturbed by HT. Metabolic profiling detected many metabolites with remarkably different relative fold abundances at different time points in the developing grain at HT versus normal temperatures, these metabolites were enriched in several HTS response pathways. The change in phytohormone ratio and auxin level might be associated with the reduction in photosynthetic products and their translocation, and ultimately with reduced starch accumulation in the developing grain. The detected metabolites might have different roles in response to the HTS in developing grain at different development stages. These results provide a theoretical reference and basis for future rice production towards higher quality and yield when grown under HTS.

Exogenous melatonin regulates endogenous phytohormone homeostasis and thiol-mediated detoxification in two indica rice cultivars under arsenic stress.

Melatonin enhanced arsenic (As) tolerance by inhibiting As bioaccumulation, modulating the expression of As transporters and phytohormone homeostasis, leading to efficient utilization of thiol machinery for sequestration and detoxification of this toxic metalloid. The present study was aimed at investigating the influence of exogenous melatonin on the regulation of endogenous plant growth regulators and their cumulative effects on metal(loid)-binding ligands in two contrasting indica rice cultivars, viz., Khitish (arsenic sensitive) and Muktashri (arsenic tolerant) under arsenic stress. Melatonin supplementation ameliorated arsenic-induced perturbations by triggering endogenous levels of gibberellic acid and melatonin, via up-regulating the expression of key biosynthetic genes like GA3ox, TDC, SNAT and ASMT. The endogenous abscisic acid content was also enhanced upon melatonin treatment by induced expression of the key anabolic gene, NCED3 and concomitant suppression of ABA8ox1. Enhanced melatonin content induced accumulation of higher polyamines (spermidine and spermine), together with up-regulation of SPDS and SPMS in Khitish, thereby modulating stress condition. On the contrary, melatonin escalated putrescine and spermidine levels in Muktashri, via enhanced expression of ADC and SAMDC. The role of melatonin appeared to be more prominent in Khitish, as evident from better utilization of thiol components like cysteine, GSH, non-protein thiols and phytochelatins, with higher GSH/GSSG ratio, despite down-regulated expression of corresponding thiol-metabolic genes (OsMT2 and OsPCS1) to deal with arsenic toxicity. The extent of arsenic bioaccumulation, which was magnified several folds, particularly in Khitish, was decreased upon melatonin application. Overall, our observation highlighted the fact that melatonin enhanced arsenic tolerance by inhibiting arsenic bioaccumulation, via modulating the expression levels of selected arsenic transporters (OsNramp1, OsPT2, OsPT8, OsLsi1) and controlling endogenous phytohormone homeostasis, leading to efficient utilization of thiol machinery for sequestration and detoxification of this toxic metalloid.

Transcriptomic insights into growth promotion effect of Trichoderma afroharzianum TM2-4 microbial agent on tomato plants

Plant growth promoting fungi are receiving increased attention as valuable beneficial microorganisms in crop cultivation due to their capacity to produce bioactive substances, promote plant growth and enhance immune defense functions. In this study, a novel Trichoderma isolate, designated as TM2-4, was screened from healthy tomato rhizosphere soil and identified as Trichoderma afroharzianum. Culture filtrate of the isolate TM2-4 displayed obvious bioactive substance production and an evident effect in promoting tomato seed germination, with hypocotyl length, radical length and vigor index increased by 28.7, 19.4 and 62.1%, respectively, after a 100-fold dilution treatment. To assess the promotion effect and related mechanism of isolate TM2-4, the plant biological indexes and gene expression profiles of tomato plants treated with or without T. afroharzianum TM2-4 microbial agent were investigated by greenhouse pot experiment and RNA sequencing. The results demonstrated that T. afroharzianum TM2-4 significantly promoted tomato plant growth in terms of plant height, dry weight, number of leaves per plant and root activity, through efficient colonization in the rhizosphere and root system of the plants. Transcriptome analyses identified a total of 984 differentially expressed genes in T. afroharzianum microbial agent inoculated tomato roots, which were mainly engaged in the biological process of phytohormone homeostasis, antioxidant activity, as well as metabolic pathways including phenylpropanoid biosynthesis and glutathione metabolism. These findings provide useful information for understanding the mechanism of isolate TM2-4 for tomato plant growth promotion, which would facilitate further development of T. afroharzianum TM2-4 microbial agent for use in vegetable crop production.

Crosstalk between phytohormones and secondary metabolites in the drought stress tolerance of crop plants: A review.

Drought stress negatively affects crop performance and weakens global food security. It triggers the activation of downstream pathways, mainly through phytohormones homeostasis and their signaling networks, which further initiate the biosynthesis of secondary metabolites (SMs). Roots sense drought stress, the signal travels to the above-ground tissues to induce systemic phytohormones signaling. The systemic signals further trigger the biosynthesis of SMs and stomatal closure to prevent water loss. SMs primarily scavenge reactive oxygen species (ROS) to protect plants from lipid peroxidation and also perform additional defense-related functions. Moreover, drought-induced volatile SMs can alert the plant tissues to perform drought stress mitigating functions in plants. Other phytohormone-induced stress responses include cell wall and cuticle thickening, root and leaf morphology alteration, and anatomical changes of roots, stems, and leaves, which in turn minimize the oxidative stress, water loss, and other adverse effects of drought. Exogenous applications of phytohormones and genetic engineering of phytohormones signaling and biosynthesis pathways mitigate the drought stress effects. Direct modulation of the SMs biosynthetic pathway genes or indirect via phytohormones' regulation provides drought tolerance. Thus, phytohormones and SMs play key roles in plant development under the drought stress environment in crop plants.

Microcutting Redox Profile and Anatomy in Eucalyptus spp. With Distinct Adventitious Rooting Competence.

Adventitious root (AR) development takes place in an intricate cellular environment. Reactive oxygen species (ROS) and antioxidant defenses, triggered by wounding in cuttings, can modulate this process. A comparative assessment of biochemical and anatomical parameters at critical rooting stages in hard- (Eucalyptus globulus Labill.) and easy- (Eucalyptus grandis W.Hill ex Maiden) to-root species was carried out. Microcuttings from seedlings were inoculated in auxin-free AR induction medium and, after 96 h, transferred to AR formation medium for a period of 24 h. Samples were collected upon excision (Texc) and at the 5th day post excision (Tform). Delayed xylem development, with less lignification, was recorded in E. globulus, when compared to E. grandis, suggesting lower activity of the cambium layer, an important site for AR development. Superoxide was more densely present around the vascular cylinder at both sampled times, and in greater quantity in E. globulus than E. grandis, declining with time in the former. Hydrogen peroxide was localized primarily along cell walls, more intensely in the primary xylem and phloem, and increased significantly at Tform in E. globulus. Ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT) activities were generally higher in E. grandis and varied as a function of time in E. globulus. Soluble guaiacol peroxidase (GPRX) activity increased from Texc to Tform in both species, whereas cell wall-bound GPRX activity increased with time in E. grandis, surpassing E. globulus. Flavonoid content increased with time in E. grandis and was higher than E. globulus at Tform. Principal component analysis showed that species- and time-derived differences contributed to almost 80% of the variance. Overall, data indicate that E. grandis shows higher cambium activity and tighter modulation of redox conditions than E. globulus. These features may influence ROS-based signaling and phytohormone homeostasis of cuttings, thereby impacting on AR development. Besides being players in the realm of AR developmental differences, the specific features herein identified could become potential tools for early clone selection and AR modulation aiming at improved clonal propagation of this forest crop.

Dynamics of miRNA mediated regulation of legume symbiosis.

Symbiotic nitrogen fixation in legume nodules is important in soils with low nitrogen availability. The initiation and sustainability of symbiosis require cellular reprogramming that involves the miRNA-mediated inhibition or activation of specific nodulation genes. The high-throughput sequencing of small RNA libraries has identified miRNAs and their targets, which are the major players in the post-transcriptional gene regulation (PTGS) of the different stages of legume-rhizobia symbiosis ranging from bacterial colonization and organogenesis to symbiotic nitrogen fixation. Here, we present an overview of information obtained from the miRNA libraries from nodulating tissues that have been sequenced to date. The functional analysis of miRNAs has revealed roles in phytohormone homeostasis and spatio-temporal regulation, as well as the mobility of miRNAs and their functions in shoot to root signalling that affects diverse functions, including bacterial entry, meristem division and differentiation, nitrogen fixation and senescence. Furthermore, small RNA fragments of rhizobial origin repress complementary plant mRNAs. We also consider the roles of miRNAs in determinate or indeterminate nodules. Taken together, this overview confirms that miRNAs are master regulators of the legume-rhizobia symbiosis.

Silicon crosstalk with reactive oxygen species, phytohormones and other signaling molecules

Exogenous applications of silicon (Si) can initiate cellular defence pathways to enhance plant resistance to abiotic and biotic stresses. Plant Si accumulation is regulated by several transporters of silicic acid (e.g. Lsi1, Lsi2, and Lsi6), but the precise mechanisms involved in overall Si transport and its beneficial effects remains unclear. In stressed plants, the accumulation of Si leads to a defence mechanism involving the formation of amorphous or hydrated silicic acid caused by their polymerization and interaction with other organic substances. Silicon also regulates plant ionic homeostasis, which involves the nutrient acquisition, availability, and replenishment in the soil through biogeochemical cycles. Furthermore, Si is implicated in modulating ethylene-dependent and jasmonate pathways, as well as other phytohormones, particularly under stress conditions. Crosstalk between Si and phytohormones could lead to improvements in Si-mediated crop growth, especially when plants are exposed to stress. The integration of Si with reactive oxygen species (ROS) metabolism appears to be a part of the signaling cascade that regulates plant phytohormone homeostasis, as well as morphological, biochemical, and molecular responses. This review aims to provide an update on Si interplays with ROS, phytohormones, and other signaling molecules that regulate plant development under stress conditions.

Molecular Aspects of Plant Growth Promotion and Protection by Bacillus subtilis.

Bacillus subtilis is one of the most widely studied plant growth-promoting rhizobacteria. It is able to promote plant growth as well as control plant pathogens through diverse mechanisms, including the improvement of nutrient availability and alteration of phytohormone homeostasis as well as the production of antimicrobials and triggering induced systemic resistance, respectively. Even though its benefits for crop production have been recognized and studied extensively under laboratory conditions, the success of its application in fields varies immensely. It is widely accepted that agricultural application of B. subtilis often fails because the bacteria are not able to persist in the rhizosphere. Bacterial colonization of plant roots is a crucial step in the interaction between microbe and plant and seems, therefore, to be of great importance for its growth promotion and biocontrol effects. A successful root colonization depends thereby on both bacterial traits, motility and biofilm formation, as well as on a signal interplay with the plant. This review addresses current knowledge about plant-microbial interactions of the B. subtilis species, including the various mechanisms for supporting plant growth as well as the necessity for the establishment of the relationship.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

Revisiting the Complex Pathosystem of Huanglongbing: Deciphering the Role of Citrus Metabolites in Symptom Development

Huanglongbing (HLB), formerly known as citrus greening disease, is one of the most devastating bacterial diseases in citrus worldwide. HLB is caused by ‘Candidatus Liberibacter asiaticus’ bacterium and transmitted by Diaphorina citri. Both ‘Ca. L. asiaticus’ and its vector manipulate the host metabolism to fulfill their nutritional needs and/or to neutralize the host defense responses. Herein, we discuss the history of HLB and the complexity of its pathosystem as well as the geographical distribution of its pathogens and vectors. Recently, our recognition of physiological events associated with ‘Ca. L. asiaticus’ infection and/or D. citri-infestation has greatly improved. However, the roles of citrus metabolites in the development of HLB symptoms are still unclear. We believe that symptom development of HLB disease is a complicated process and relies on a multilayered metabolic network which is mainly regulated by phytohormones. Citrus metabolites play vital roles in the development of HLB symptoms through the modulation of carbohydrate metabolism, phytohormone homeostasis, antioxidant pathways, or via the interaction with other metabolic pathways, particularly involving amino acids, leaf pigments, and polyamines. Understanding how ‘Ca. L. asiaticus’ and its vector, D. citri, affect the metabolic pathways of their host is critical for developing novel, sustainable strategies for HLB management.

Expression of a carotenogenic gene allows faster biomass production by redesigning plant architecture and improving photosynthetic efficiency in tobacco.

Because carotenoids act as accessory pigments in photosynthesis, play a key photoprotective role and are of major nutritional importance, carotenogenesis has been a target for crop improvement. Although carotenoids are important precursors of phytohormones, previous genetic manipulations reported little if any effects on biomass production and plant development, but resulted in specific modifications in carotenoid content. Unexpectedly, the expression of the carrot lycopene β-cyclase (DcLCYB1) in Nicotiana tabacum cv. Xanthi not only resulted in increased carotenoid accumulation, but also in altered plant architecture characterized by longer internodes, faster plant growth, early flowering and increased biomass. Here, we have challenged these transformants with a range of growth conditions to determine the robustness of their phenotype and analyze the underlying mechanisms. Transgenic DcLCYB1 lines showed increased transcript levels of key genes involved in carotenoid, chlorophyll, gibberellin (GA) and abscisic acid (ABA) biosynthesis, but also in photosynthesis-related genes. Accordingly, their carotenoid, chlorophyll, ABA and GA contents were increased. Hormone application and inhibitor experiments confirmed the key role of altered GA/ABA contents in the growth phenotype. Because the longer internodes reduce shading of mature leaves, induction of leaf senescence was delayed, and mature leaves maintained a high photosynthetic capacity. This increased total plant assimilation, as reflected in higher plant yields under both fully controlled constant and fluctuating light, and in non-controlled conditions. Furthermore, our data are a warning that engineering of isoprenoid metabolism can cause complex changes in phytohormone homeostasis and therefore plant development, which have not been sufficiently considered in previous studies.

Effects of dibutyl phthalate contamination on physiology, phytohormone homeostasis, rhizospheric and endophytic bacterial communities of Brassica rapa var. chinensis

Phthalates are plasticizers and are ubiquitously detected in the environment, frequently at mg/kg levels. The present study aimed to evaluate the effects of dibutyl phthalate (DBP) on germination, growth, enzyme activity, phytohormone homeostasis and bacterial communities of two cultivars of Brassica rapa var. chinensis. The germination rate was decreased up to 20% compared to the control, and the growth of the vegetables was severely inhibited at the early stage when exposed to DBP at 20 mg/kg. Antioxidant defense enzyme activities and malondialdehyde (MDA) content increased upon exposure to DBP. A dose-response of auxin (IAA) was observed after a 2 d exposure. Gibberellin (GA3) and abscisic acid (ABA) responded at day 10 under DBP stress. GA3 did not show a clear dose-response effect and ABA increased about 3 times as the DBP concentration increased from 2 to 20 mg/L. Microbial population shifts were observed, especially in rhizosphere soil and roots. No obvious change occurred for the α diversity of rhizospheric bacteria among different treatments. Chao1, Shannon and Simpson indices of the root endophytic bacteria showed a decreasing trend with increasing DBP supplementation, while all the indices increased in shoot endophytic bacteria in comparison to the control. The results indicated that exposure to DBP may compromise the fitness of the leafy vagetables and alter the endophytic and rhizospheric bacteria, which might further affect the nutrients of the vegetables and alter ecosystem functions.

Hormonal response of Acutodesmus obliquus exposed to combined treatment with 24-epibrassinolide and lead

Phytohormones play key roles in many aspects of plant growth and development, as well as in resistance to abiotic stresses. The presence of heavy metal limits phytohormone endogenous level; however, the application of brassinosteroids (BRs) restores phytohormone homeostasis and reduces unfavorable consequences of heavy metal on plant growth. Therefore, the aim of this study was to (1) broaden previously published analyses/findings to study the effect of 24-epibrassinolide (EBL) and/or lead (Pb) on Acutodesmus obliquus phytohormone level after 5 days of cultivation using LC-QToF-MS quantification technique and (2) extend the total amount of quantified phytohormones in A. obliquus. The study confirmed that exogenous EBL increased the contents of gibberellin A3 (GA3), auxins (AXs) (indole-3-acetic acid, phenylacetic acid), BRs brassinolide, 24-epibrassinolide (EBL), 28-homobrassinolide, castasterone, 24-epicastasterone, typhasterol, cathasterone, 6-deoxotyphasterol, as well as different types of cytokinins (CKs): free bases, ribosides, and conjugates (N- and O-glucosides). On the other hand, treatment with Pb had an opposite effect on BRs, GA3, AXs, and free bases, as well as ribosides of CKs. The abscisic acid (ABA) level decreased under EBL treatment but increased in response to Pb stress. The level of N-glucosides, as well as O-glucosides of CKs, also significantly increased in response to Pb alone. Interestingly, the co-application of EBL and Pb led to an increase in BRs, GA3, AXs, and CKs content in the algae. Principal component analysis revealed that based on treatments, increase of GA3, BRs, and AXs was found to be in the following order: 1 μM EBL > 0.01 μM Pb + 1 μM EBL > 500 μM Pb + 1 μM EBL > control > 0.01 μM Pb > 500 μM Pb. Moreover, very strong significant linear relations between almost all studied AXs and BRs were noted. Summarizing, this research did not only allow to detect the occurrence of ABA, GA3, AXs, BRs, and CKs in A. obliquus for the first time but also to study the combined action of EBL and Pb, as well as compare it with treatment alone.

Involvement of Arabidopsis BIG protein in cell death mediated by Myo-inositol homeostasis

Programmed cell death (PCD) is essential for several aspects of plant life. We previously identified the mips1 mutant of Arabidopsis thaliana, which is deficient for the enzyme catalysing myo-inositol synthesis, and that displays light-dependent formation of lesions on leaves due to Salicylic Acid (SA) over-accumulation. Rationale of this work was to identify novel regulators of plant PCD using a genetic approach. A screen for secondary mutations that abolish the mips1 PCD phenotype identified a mutation in the BIG gene, encoding a factor of unknown molecular function that was previously shown to play pleiotropic roles in plant development and defence. Physiological analyses showed that BIG is required for lesion formation in mips1 via SA-dependant signalling. big mutations partly rescued transcriptomic and metabolomics perturbations as stress-related phytohormones homeostasis. In addition, since loss of function of the ceramide synthase LOH2 was not able to abolish cell death induction in mips1, we show that PCD induction is not fully dependent of sphingolipid accumulation as previously suggested. Our results provide further insights into the role of the BIG protein in the control of MIPS1-dependent cell death and also into the impact of sphingolipid homeostasis in this pathway.

ERECTA1 Acts Upstream of the OsMKKK10-OsMKK4-OsMPK6 Cascade to Control Spikelet Number by Regulating Cytokinin Metabolism in Rice.

Grain number is a flexible trait that strongly contributes to grain yield. In rice (Oryza sativa), the OsMKKK10-OsMKK4-OsMPK6 cascade, which is negatively regulated by the dual-specificity phosphatase GSN1, coordinates the trade-off between grain number and grain size. However, the specific components upstream and downstream of the GSN1-MAPK module that regulate spikelet number per panicle remain obscure. Here, we report that ERECTA1 (OsER1), a negative regulator of spikelet number per panicle, acts upstream of the OsMKKK10-OsMKK4-OsMPK6 cascade and that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway is required to maintain cytokinin homeostasis. OsMPK6 directly interacts with and phosphorylates the zinc finger transcription factor DST to enhance its transcriptional activation of CYTOKININ OXIDASE2 (OsCKX2), indicating that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway shapes panicle morphology by regulating cytokinin metabolism. Furthermore, overexpression of either DST or OsCKX2 rescued the spikelet number phenotype of the oser1, osmkkk10, osmkk4, and osmpk6 mutants, suggesting that the DST-OsCKX2 module genetically functions downstream of the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway. These findings reveal specific crosstalk between a MAPK signaling pathway and cytokinin metabolism, shedding light on how developmental signals modulate phytohormone homeostasis to shape the inflorescence.