Cloning of CAT genes in Satsuma mandarin and their expression characteristics in response to environmental stress and arbuscular mycorrhizal fungi.

KEY MESSAGE: CitCAT1 and CitCAT2 were cloned and highly expressed in mature leaves. High temperatures up-regulated CitCAT1 expression, while low temperatures and Diversispora versiformis up-regulated CitCAT2 expression, maintaining a low oxidative damage. Catalase (CAT), a tetrameric heme-containing enzyme, removes hydrogen peroxide (H2O2) to maintain low oxidative damage in plants exposed to environmental stress. This study aimed to clone CAT genes from Citrus sinensis cv. "Oita 4" and analyze their expression patterns in response to environmental stress, exogenous abscisic acid (ABA), and arbuscular mycorrhizal fungal inoculation. Two CAT genes, CitCAT1 (NCBI accession: PP067858) and CitCAT2 (NCBI accession: PP061394) were cloned, and the open reading frames of their proteins were 1479 bp and 1539 bp, respectively, each encoding 492 and 512 amino acids predicted to be localized in the peroxisome, with CitCAT1 being a stable hydrophilic protein and CitCAT2 being an unstable hydrophilic protein. The similarity of their amino acid sequences reached 83.24%, and the two genes were distantly related. Both genes were expressed in stems, leaves, flowers, and fruits, accompanied by the highest expression in mature leaves. In addition, CitCAT1 expression was mainly up-regulated by high temperatures (37 °C), exogenous ABA, and PEG stress within a short period of time, whereas CitCAT2 expression was up-regulated by exogenous ABA and low-temperature (4 °C) stress. Low temperatures (0 °C) for 12 h just up-regulated CitCAT2 expression in Diversispora versiformis-inoculated plants, and D. versiformis inoculation up-regulated CitCAT2 expression, along with lower hydrogen peroxide and malondialdehyde levels in mycorrhizal plants at low temperatures. It is concluded that CitCAT2 has an important role in resistance to low temperatures as well as mycorrhizal enhancement of host resistance to low temperatures.

Serendipita indica mitigates drought-triggered oxidative burst in trifoliate orange by stimulating antioxidant defense systems.

Soil drought is detrimental to plant growth worldwide, particularly by triggering reactive oxygen species (ROS) burst. Serendipita indica (Si), a culturable root-associated endophytic fungus, can assist host plants in dealing with abiotic stresses; however, it is unknown whether and how Si impacts the drought tolerance of citrus plants. To unravel the effects and roles of Si on drought-stressed plants, trifoliate orange (Poncirus trifoliata L. Raf.; a citrus rootstock) seedlings were inoculated with Si and exposed to soil drought, and growth, gas exchange, ROS levels, antioxidant defense systems, and expression of genes encoding antioxidant enzymes and fatty acid desaturases in leaves were measured. Soil drought suppressed plant biomass, whereas Si inoculation significantly increased plant biomass (10.29%-22.47%) and shoot/root ratio (21.78%-24.68%) under ample water and drought conditions, accompanied by improved net photosynthetic rate (105.71%), water use efficiency (115.29%), chlorophyll index (55.34%), and nitrogen balance index (63.84%) by Si inoculation under soil drought. Soil drought triggered an increase in leaf hydrogen peroxide and superoxide anion levels, while Si inoculation significantly reduced these ROS levels under soil drought, resulting in lower membrane lipid peroxidation with respect to malondialdehyde changes. Furthermore, Si-inoculated seedlings under soil drought had distinctly higher levels of ascorbate and glutathione, as well as catalase, peroxidase, and glutathione peroxidase activities, compared with no-Si-inoculated seedlings. Si inoculation increased the expression of leaf PtFAD2, PtFAD6, PtΔ9, PtΔ15, PtFe-SOD, PtCu/Zn-SOD, PtPOD, and PtCAT1 genes under both ample water and soil drought conditions. Overall, Si-inoculated trifoliate orange plants maintained a low oxidative burst in leaves under drought, which was associated with stimulation of antioxidant defense systems. Therefore, Si has great potential as a biostimulant in enhancing drought tolerance in plants, particularly citrus.

Mycorrhizal Fungal Effects on Plant Growth, Osmolytes, and CsHsp70s and CsPIPs Expression in Leaves of Cucumber under a Short-Term Heat Stress.

Arbuscular mycorrhizal (AM) fungi enhance plant stress tolerance, but it is unclear whether AM fungi affect heat tolerance in cucumbers. This study aimed to analyze how an AM fungus, Diversispora versiformis, affected growth, chlorophyll, five osmolytes, and plasma membrane intrinsic proteins (PIPs) and heat shock protein 70 (Hsp70) gene expression in cucumber leaves after a short-term (80 h) heat stress. Heat treatment significantly reduced root AM fungal colonization rate (0.26 folds). Heat treatment also distinctly suppressed plant height, stem diameter, and biomass, whereas AM fungal inoculation improved these growth variables as well as the chlorophyll index, with the benefit being more obvious under heat than under no-heat stress conditions. Heat treatment triggered differential changes in osmolytes (sucrose, fructose, and betaine) of inoculated and uninoculated cucumbers, whereas inoculation with AM fungus significantly raised leaf sucrose, fructose, glucose, betaine, and proline levels when compared to non-AM fungal inoculation. Heat treatment increased the expression of two (CsPIP1;6 and CsPIP2;1) of eight CsPIPs in inoculated and uninoculated plants, whereas AM fungal inoculation up-regulated the expression of CsPIP1;6, CsPIP2;1, and CsPIP2;6 under heat stress conditions. Hsp70s expressed differently in inoculated and uninoculated plants under heat versus no-heat stress, with 6 of 11 CsHsp70s down-regulated in inoculated plants. Under heat stress conditions, AM fungus only up-regulated CsHsp70-8 expression in 11 Hsp70s, while another eight CsHsp70s were down-regulated. Heat treatment and AM fungal inoculation both increased the expression of CsHsp70-8 and CsPIP1;6. It was concluded that AM fungus-inoculated cucumbers have high levels of growth, chlorophyll, and osmolytes under heat stress and do not require high CsPIPs and CsHsp70s expression to tolerate a short-term heat treatment.

Exogenous Melatonin Regulates Physiological Responses and Active Ingredient Levels in Polygonum cuspidatum under Drought Stress.

Polygonum cuspidatum, an important medicinal plant, is rich in resveratrol and polydatin, but it frequently suffers from drought stress in the nursery stage, which inhibits the plant's growth, active components concentrations, and the price of rhizome in the later stage. The purpose of this study was to analyze how exogenous 100 mM melatonin (MT) (an indole heterocyclic compound) affected biomass production, water potential, gas exchange, antioxidant enzyme activities, active components levels, and resveratrol synthase (RS) gene expression of P. cuspidatum seedlings growing under well-watered and drought stress conditions. The 12-week drought treatment negatively affected the shoot and root biomass, leaf water potential, and leaf gas exchange parameters (photosynthetic rate, stomatal conductance, and transpiration rate), whereas the application of exogenous MT significantly increased these variables of stressed and non-stressed seedlings, accompanied by higher increases in the biomass, photosynthetic rate, and stomatal conductance under drought versus well-watered conditions. Drought treatment raised the activities of superoxide dismutase, peroxidase, and catalase in the leaves, while the MT application increased the activities of the three antioxidant enzymes regardless of soil moistures. Drought treatment reduced root chrysophanol, emodin, physcion, and resveratrol levels, while it dramatically promoted root polydatin levels. At the same time, the application of exogenous MT significantly increased the levels of the five active components, regardless of soil moistures, with the exception of no change in the emodin under well-watered conditions. The MT treatment also up-regulated the relative expression of PcRS under both soil moistures, along with a significantly positive correlation between the relative expression of PcRS and resveratrol levels. In conclusion, exogenous MT can be employed as a biostimulant to enhance plant growth, leaf gas exchange, antioxidant enzyme activities, and active components of P. cuspidatum under drought stress conditions, which provides a reference for drought-resistant cultivation of P. cuspidatum.

Serendipita indica promotes P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and phosphate transporter gene expression.

The culturable endophytic fungus Serendipita indica has many beneficial effects on plants, but whether and how it affects physiological activities and phosphorus (P) acquisition of tea seedlings at low P levels is unclear. The objective of this study was to analyze the effects of inoculation with S. indica on growth, gas exchange, chlorophyll fluorescence, auxins, cytokinins, P levels, and expressions of two phosphate transporter (PT) genes in leaves of tea (Camellia sinensis L. cv. Fudingdabaicha) seedlings grown at 0.5 µM (P0.5) and 50 µM (P50) P levels. Sixteen weeks after the inoculation, S. indica colonized roots of tea seedlings, with root fungal colonization rates reaching 62.18% and 81.34% at P0.5 and P50 levels, respectively. Although plant growth behavior, leaf gas exchange, chlorophyll values, nitrogen balance index, and chlorophyll fluorescence parameters of tea seedlings were suppressed at P0.5 versus P50 levels, inoculation of S. indica mitigated the negative effects to some extent, along with more prominent promotion at P0.5 levels. S. indica inoculation significantly increased leaf P and indoleacetic acid concentrations at P0.5 and P50 levels and leaf isopentenyladenine, dihydrozeatin, and transzeatin concentrations at P0.5 levels, coupled with the reduction of indolebutyric acid at P50 levels. Inoculation of S. indica up-regulated the relative expression of leaf CsPT1 at P0.5 and P50 levels and CsPT4 at P0.5 levels. It is concluded that S. indica promoted P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and CsPT1 and CsPT4 expression.

Two different strategies of Diversispora spurca-inoculated walnut seedlings to improve leaf P acquisition at low and moderate P levels.

Walnut (Juglans regia) is an important nut tree species in the world, whereas walnut trees often face inadequate phosphorus (P) levels of soil, negatively limiting its growth and yield. Arbuscular mycorrhizal fungi (AMF) can colonize walnut roots, but whether and how AMF promotes walnut growth, physiological activities, and P acquisition is unclear. The present study aimed to evaluate the effects of Diversispora spurca on plant growth, chlorophyll component concentrations, leaf gas exchange, sugar and P concentrations, and expression of purple acid phosphatase (PAP) and phosphate transporter (PT) genes in leaves of J. regia var. Liaohe 1 seedling under moderate (100 µmol/L P) and low P (1 µmol/L P) levels conditions. Three months after inoculation, the root mycorrhizal colonization rate and soil hyphal length were 45.6-53.2% and 18.7-39.9 cm/g soil, respectively, and low P treatment significantly increased both root mycorrhizal colonization rate and soil hyphal length. Low P levels inhibited plant growth (height, stem diameter, and total biomass) and leaf gas exchange (photosynthetic rate, transpiration rate and stomatal conductance), while AMF colonization significantly increased these variables at moderate and low P levels. Low P treatment limited the level of chlorophyll a, but AMF colonization did not significantly affect the level of chlorophyll components, independent on soil P levels. AMF colonization also increased leaf glucose at appropriate P levels and leaf fructose at low P levels than non-AMF treatment. AMF colonization significantly increased leaf P concentration by 21.0-26.2% than non-AMF colonization at low and moderate P levels. Low P treatment reduced the expression of leaf JrPAP10, JrPAP12, and JrPT3;2 in the inoculated plants, whereas AMF colonization up-regulated the expression of leaf JrPAP10, JrPAP12, and JrPT3;2 at moderate P levels, although AMF did not significantly alter the expression of JrPAPs and JrPTs at low P levels. It is concluded that AMF improved plant growth, leaf gas exchange, and P acquisition of walnut seedlings at different P levels, where mycorrhizal promotion of P acquisition was dominated by direct mycorrhizal involvement in P uptake at low P levels, while up-regulation of host PAPs and PTs expressions at moderate P levels.

Effects of Organophosphate-Degrading Bacteria on the Plant Biomass, Active Medicinal Components, and Soil Phosphorus Levels of Paris polyphylla var. yunnanensis.

Paris polyphylla var. yunnanensis, a medicinal plant that originated in Yunnan (China), has been over-harvested in the wild population, resulting in its artificial cultivation. Given the negative environmental impacts of the excessive use of phosphorus (P) fertilization, the application of organophosphate-degrading bacteria (OPDB) is a sustainable approach for improving the P use efficiency in Paris polyphylla var. yunnanensis production. The present work aimed to analyze the effects of three organic phosphate-solubilizing bacteria of Bacillus on the yield and quality of P. polyphylla var. yunnanensis and the P concentrations in the soil. All the inoculation treatments distinctly increased the rhizome biomass, steroidal, and total saponin concentrations of the rhizomes and the Olsen-P and organic P in the soil. The highest growth rate of rhizomes biomass, steroidal saponins, available phosphorus, and total phosphorus content was seen in the S7 group, which was inoculated with all three OPDB strains, showing increases of 134.58%, 132.56%, 51.64%, and 17.19%, respectively. The highest total saponin content was found in the group inoculated with B. mycoides and B. wiedmannii, which increased by 33.68%. Moreover, the highest organic P content was seen in the group inoculated with B. wiedmannii and B. proteolyticus, which increased by 96.20%. In addition, the rhizome biomass was significantly positively correlated with the saponin concentration, together with the positive correlation between the Olsen-P and organic P and total P. It is concluded that inoculation with organophosphate-degrading bacteria improved the biomass and medicinal ingredients of the rhizome in P. polyphylla var. yunnanensis, coupled with increased soil P fertility, with a mixture of the three bacteria performing best.

Metabolomics reveals arbuscular mycorrhizal fungi-mediated tolerance of walnut to soil drought.

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) have a positive effect on drought tolerance of plants after establishing reciprocal resymbiosis with roots, while the underlying mechanism is not deciphered. Metabolomics can explain the mechanism of plant response to environmental stress by analyzing the changes of all small molecular weight metabolites. The purpose of this study was to use Ultra High Performance Liquid Chromatography Q Exactive Mass Spectrometer to analyze changes in root metabolites of walnut (Juglans regia) after inoculation with an arbuscular mycorrhizal fungus Diversispora spurca under well-watered (WW) and drought stress (DS). RESULTS: Sixty days of soil drought significantly inhibited root mycorrhizal colonization rate, shoot and root biomass production, and leaf water potential in walnut, while AMF inoculation significantly increased biomass production and leaf water potential, accompanied by a higher increase magnitude under DS versus under WW. A total of 3278 metabolites were identified. Under WW, AMF inoculation up-regulated 172 metabolites and down-regulated 61 metabolites, along with no changes in 1104 metabolites. However, under DS, AMF inoculation up-regulated 49 metabolites and down-regulated 116 metabolites, coupled with no changes in 1172 metabolites. Among them, juglone (a quinone found in walnuts) as the first ranked differential metabolite was up-regulated by AMF under WW but not under DS; 2,3,5-trihydroxy-5-7-dimethoxyflavanone as the first ranked differential metabolite was increased by AMF under DS but not under WW. The KEGG annotation showed a large number of metabolic pathways triggered by AMF, accompanied by different metabolic pathways under WW and DS. Among them, oxidative phosphorylation and phenylalanine metabolism and biosynthesis were triggered by AMF in response to WW and DS, where N-acetyl-L-phenylalanine was induced by AMF to increase under DS, while decreasing under WW. CONCLUSION: This study provides new insights into the metabolic mechanisms of mycorrhiza-enhanced drought tolerance in walnuts.

An endophytic fungus, Piriformospora indica, enhances drought tolerance of trifoliate orange by modulating the antioxidant defense system and composition of fatty acids.

A cultivable endophytic fungus, Piriformospora indica, improves growth and enhances stress tolerance of host plants, but the underlying mechanisms remain unknown. We hypothesized that P. indica enhanced the drought tolerance of the host by regulating the antioxidant defense system and composition of fatty acids. Trifoliate orange (Poncirus trifoliata) seedlings were inoculated with P. indica under ample water and drought stress to analyze the change in plant growth, reactive oxygen species (ROS) levels, antioxidant enzyme activities, non-enzymatic antioxidant concentrations, fatty acid compositions, and expressions of both antioxidant enzyme genes and fatty acid desaturase (FAD) genes. The 9-week soil water deficit significantly increased the colonization of P. indica to roots, and P. indica promoted the increase of shoot biomass under drought. Soil drought triggered an elevation of hydrogen peroxide in roots, while the inoculated plants had lower levels of ROS (hydrogen peroxide and superoxide anion radicals) and lower degree of membrane lipid peroxidation (based on malondialdehyde levels) under drought. Drought treatment also elevated ascorbic acid and glutathione concentrations, and the elevation was further amplified after P. indica inoculation. Inoculated plants under drought also recorded significantly higher iron-superoxide dismutase (Fe-SOD), manganese-superoxide dismutase (Mn-SOD), peroxidases, catalase, glutathione reductase and ascorbate peroxidase activities, accompanied by up-regulation of PtFe-SOD and PtCu/Zn-SOD expressions. Inoculation with P. indica significantly increased total saturated fatty acids (e.g., C6:0, C15:0, C16:0, C23:0 and C24:0) concentration and reduced total unsaturated fatty acids (e.g., C18:1N9C, C18:2N6, C18:3N3, C18:1N12 and C19:1N9T) concentrations, leading to a decrease in the unsaturation index of fatty acids, which may be associated with the up-regulation of PtFAD2 and PtFAD6 and down-regulation of PtΔ9. It was concluded that the colonization of P. indica can activate enzyme and non-enzyme defense systems and regulate the composition of fatty acids under drought, thus alleviating the oxidative damage to the host caused by drought.

Extraradical Mycorrhizal Hyphae Promote Soil Carbon Sequestration through Difficultly Extractable Glomalin-Related Soil Protein in Response to Soil Water Stress.

Soil water stress (WS) affects the decomposition of soil organic carbon (SOC) and carbon (C) emissions. Glomalin, released by arbuscular mycorrhizal fungi into soil that has been defined as glomalin-related soil protein (GRSP), is an important pool of SOC, with hydrophobic characteristics. We hypothesized that mycorrhizal fungi have a positive effect on SOC pools under soil WS for C sequestration in GRSP secreted by extraradical mycorrhizal hyphae. A microsystem was used to establish a root chamber (co-existence of roots and extraradical mycorrhizal hyphae) and a hyphal chamber (the presence of extraradical mycorrhizal hyphae) to study changes in plant growth, leaf water potential, soil aggregate stability, SOC, GRSP, C concentrations in GRSP (CGRSP), and the contribution of CGRSP to SOC after inoculating Rhizophagus intraradices with trifoliate orange (Poncirus trifoliata) in the root chamber under adequate water (AW) and WS. Inoculation with R. intraradices alleviated negative effects on leaf water potential and plant growth after 7 weeks of WS. Soil WS decreased SOC and mean weight diameter (MWD), while AMF inoculation led to an increase in SOC and MWD in both chambers, with the most prominent increase in the hyphal chamber under WS. The C concentration in easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 7.32 - 12.57 and 24.90 - 32.60 mg C/g GRSP, respectively. WS reduced CGRSP, while AMF mitigated the reduction. Extraradical mycorrhizal hyphae increased GRSP production and CGRSP, along with a more prominent increase in DE-GRSP under WS than under AW. Extraradical mycorrhizal hyphae increased the contribution of CDE-GRSP to SOC only under WS. CEE-GRSP and CDE-GRSP were significantly positively correlated with SOC and MWD. It is concluded that extraradical mycorrhizal hyphae prominently promoted C sequestration of recalcitrant DE-GRSP under soil WS, thus contributing more organic C accumulation and preservation in aggregates and soil C pool.

Mycorrhizal Effects on Growth and Expressions of Stress-Responsive Genes (aquaporins and SOSs) of Tomato under Salt Stress.

Environmentally friendly arbuscular mycorrhizal fungi (AMF) in the soil can alleviate host damage from abiotic stresses, but the underlying mechanisms are unclear. The objective of this study was to analyze the effects of an arbuscular mycorrhizal fungus, Paraglomus occultum, on plant growth, nitrogen balance index, and expressions of salt overly sensitive genes (SOSs), plasma membrane intrinsic protein genes (PIPs), and tonoplast intrinsic protein genes (TIPs) in leaves of tomato (Solanum lycopersicum L. var. Huapiqiu) seedlings grown in 0 and 150 mM NaCl stress. NaCl stress severely inhibited plant growth, but P. occultum inoculation significantly improved plant growth. NaCl stress also suppressed the chlorophyll index, accompanied by an increase in the flavonoid index, whereas inoculation with AMF significantly promoted the chlorophyll index as well as reduced the flavonoid index under NaCl conditions, thus leading to an increase in the nitrogen balance index in inoculated plants. NaCl stress regulated the expression of SlPIP1 and SlPIP2 genes in leaves, and five SlPIPs genes were up-regulated after P. occultum colonization under NaCl stress, along with the down-regulation of only SlPIP1;2. Both NaCl stress and P. occultum inoculation induced diverse expression patterns in SlTIPs, coupled with a greater number of up-regulated TIPs in inoculated versus uninoculated plants under NaCl stress. NaCl stress up-regulated SlSOS2 expressions of mycorrhizal and non-mycorrhizal plants, while P. occultum significantly up-regulated SlSOS1 expressions by 1.13- and 0.45-fold under non-NaCl and NaCl conditions, respectively. It was concluded that P. occultum inoculation enhanced the salt tolerance of the tomato, associated with the nutrient status and stress-responsive gene (aquaporins and SOS1) expressions.

Arbuscular mycorrhiza induces low oxidative burst in drought-stressed walnut through activating antioxidant defense systems and heat shock transcription factor expression.

Arbuscular mycorrhizal fungi (AMF) have important roles in enhancing drought tolerance of host plants, but it is not clear whether and how AMF increase drought tolerance in walnut (Juglans regia). We hypothesized that AMF could activate antioxidant defense systems and heat shock transcription factors (Hsfs) transcription levels to alleviate oxidative damage caused by drought. The walnut variety 'Liaohe No. 1' was inoculated with Diversispora spurca and exposed to well-watered (WW, 75% of the maximum soil water capacity) and drought stress (DS, 50% of the maximum soil water capacity) for 6 weeks. Plant growth, antioxidant defense systems, and expressions of five JrHsfs in leaves were studied. Such drought treatment inhibited root mycorrhizal colonization, while plant growth performance was still improved by AMF inoculation. Mycorrhizal fungal inoculation triggered the increase in soluble protein, glutathione (GSH), ascorbic acid (ASC), and total ASC contents and ascorbic peroxidase and glutathione reductase activities, along with lower hydrogen peroxide (H2O2), superoxide anion radical (O2 •-), and malondialdehyde (MDA) levels, compared with non-inoculation under drought. Mycorrhizal plants also recorded higher peroxidase, catalase, and superoxide dismutase activities than non-mycorrhizal plants under drought. The expression of JrHsf03, JrHsf05, JrHsf20, JrHsf22, and JrHsf24 was up-regulated under WW by AMF, while the expression of JrHsf03, JrHsf22, and JrHsf24 were up-regulated only under drought by AMF. It is concluded that D. spurca induced low oxidative burst in drought-stressed walnut through activating antioxidant defense systems and part Hsfs expressions.

Insights into the molecular aspects of salt stress tolerance in mycorrhizal plants.

Salt stress is one of the major abiotic stresses that severely affect plant growth and yield, and also affect the livelihood of people all around the world. Arbuscular mycorrhizal fungi (AMF) colonize majority of terrestrial plants, including halophytes, xerophytes and glycophytes, and facilitate their functioning by various physiological, biochemical and molecular processes. In the past two decades, significant progress has been made to understand the role of AMF in mitigating salt stress and improving plant growth and productivity under saline conditions. Several studies focusing on the biochemical and physiological mechanisms that mycorrhizal plants employ to combat salt stress have been carried out. This review reinforces such studies and gives further insights into the molecular aspects of tolerance to salt stress in the plants colonized by AMF. It emphasises on the role of AMF in sensing and signalling salt stress, expression of aquaporin-encoding genes, Na+/H+ antiporters and transporters involved in Na+ exclusion, CNGCs and late embryogenesis abundant proteins in relation to salt stress tolerance. Further, this paper also reviews the accrual of compatible osmolytes, phytohormones and nitric oxide for understanding the benefits of this symbiosis under saline environment, and provides a benchmark information to understand the contribution of mycorrhizal symbiosis at molecular level and will attract attention of researchers to develop and highlight the future research programs in this field.

Multi-Omics and Integrative Approach towards Understanding Salinity Tolerance in Rice: A Review.

Rice (Oryza sativa L.) plants are simultaneously encountered by environmental stressors, most importantly salinity stress. Salinity is the major hurdle that can negatively impact growth and crop yield. Understanding the salt stress and its associated complex trait mechanisms for enhancing salt tolerance in rice plants would ensure future food security. The main aim of this review is to provide insights and impacts of molecular-physiological responses, biochemical alterations, and plant hormonal signal transduction pathways in rice under saline stress. Furthermore, the review highlights the emerging breakthrough in multi-omics and computational biology in identifying the saline stress-responsive candidate genes and transcription factors (TFs). In addition, the review also summarizes the biotechnological tools, genetic engineering, breeding, and agricultural practicing factors that can be implemented to realize the bottlenecks and opportunities to enhance salt tolerance and develop salinity tolerant rice varieties. Future studies pinpointed the augmentation of powerful tools to dissect the salinity stress-related novel players, reveal in-depth mechanisms and ways to incorporate the available literature, and recent advancements to throw more light on salinity responsive transduction pathways in plants. Particularly, this review unravels the whole picture of salinity stress tolerance in rice by expanding knowledge that focuses on molecular aspects.

Arbuscular mycorrhizal fungi and phosphorus supply accelerate main medicinal component production of Polygonum cuspidatum.

The medicinal plant Polygonum cuspidatum Sieb. Et Zucc is rich in stilbenes (e.g., polygonin and resveratrol) and anthraquinones (e.g., emodin) for the therapy of human diseases, while how to increase the growth and medicinal composition concentrations of P. cuspidatum has become an urgent issue. The aim of the present study was to evaluate the effects of inoculation with an arbuscular mycorrhizal (AM) fungus, Funneliformis mosseae, on plant growth, phosphorus (P) acquisition, medicinal component concentrations, and expressions of resveratrol synthesis-associated enzyme genes of P. cuspidatum at two P levels (0 M and 0.2 M). P supply (0.2 M) stimulated root AM fungal colonization rate. F. mosseae inoculation significantly improved growth performance (height, diameter, and biomass) and root morphology (diameter, length, and projected area), irrespectively of substrate P levels. P supply and F. mosseae distinctly increased soil acid and neutral phosphatase activities, as well as root P concentrations. P supply increased root physcion and resveratrol concentrations in inoculated and uninoculated plants, along with up-regulated expressions of PcCHS1, PcCRS1, PcRS11, and PcSTS. AM plants represented significantly higher root aloe-emodin, chrysophanol, emodin, physcion, polydatin, and resveratrol concentrations than non-AM plants irrespective of P levels, coupled with up-regulated expressions of PcCHS1, PcCHS2, PcRS11, PcRS, and PcSTS. It is concluded that 0.2 M P supply and F. mosseae inoculation promoted chrysophanol, physcion, polydatin, and resveratrol concentrations of P. cuspidatum, with the increase in resveratrol associated with up-regulated expressions of related genes.

Symbiotic Fungi Alter the Acquisition of Phosphorus in Camellia oleifera through Regulating Root Architecture, Plant Phosphate Transporter Gene Expressions and Soil Phosphatase Activities.

Plant roots can be colonized by many symbiotic fungi, whereas it is unclear whether and how symbiotic fungi including arbuscular mycorrhizal fungi and endophytic fungi promote phosphorus (P) uptake in Camellia oleifera plants. The objective of the present study was to analyze the effect of inoculation with a culturable endophytic fungus (Piriformospora indica), three arbuscular mycorrhizal fungi (Funneliformis mosseae, Diversispora versiformis, and Rhizophagus intraradices), and mixture of F. mosseae, D. versiformis and R. intraradices on plant growth, root architecture, soil Olsen-P, soil phosphatase activities, leaf and root P concentrations, and phosphate transporter gene expressions, in order to explore the potential and mechanism of these symbiotic fungi on P acquisition. All the symbiotic fungi colonized roots of C. oleifera after 16 weeks, with P. indica showing the best effect on fungal colonization. All the symbiotic fungi significantly increased acid, neutral, and total phosphatase activities in the soil, accompanied with an elevation of soil Olsen-P, of which P. indica presented the best effect. All symbiotic fungal treatments, except D. versiformis, significantly promoted plant growth, coupled with an increase in root total length, area, and volume. Symbiotic fungi almost up-regulated root CoPHO1-3 expressions as well as leaf CoPHO1-1, CoPHO1-3, and CoPHT1;4 expressions. Correlation analysis showed that P concentrations in leaves and roots were significantly positively correlated with root morphological variables (length, volume, and surface area) and soil acid, neutral and total phosphatase activities. It is concluded that symbiotic fungi, especially P. indica, played an important role in P uptake of C. oleifera plants through regulating root architecture, part plant phosphate transporter gene expressions and soil phosphatase activities.

Endophytic fungus Serendipita indica accelerates ascorbate-glutathione cycle of white clover in response to water stress.

Ascorbate-glutathione cycle is an important pathway for plants to scavenge reactive oxygen species (ROS) under environmental stress conditions. The objective of this study was to investigate the effects of the endophytic fungus Serendipita indica on biomass, chlorophyll concent, ROS levels, antioxidant enzyme activities, and ascorbate-glutathione cycle in white clover under ample water and water stress conditions. The results showed that 46 days of soil water stress distinctly promoted root colonization by S. indica. Under water stress, S. indica inoculation significantly promoted shoot and root biomass, total chlorophyll content, and activities of superoxide dismutases (SOD; e.g., Fe-SOD and Cu/Zn-SOD) and peroxidase in roots, coupled with a decrease in malondialdehyde content in roots. In the ascorbate-glutathione cycle of roots, S. indica also significantly increased the activity of ascorbate peroxidase and glutathione reductase activities in water-stressed white clover, along with the increase in reduced ascorbic acid and reduced/oxidized glutathione contents, thus accelerating the ascorbate-glutathione cycle in inoculated plants to scavenge more ROS (e.g., hydrogen peroxide). As a result, S. indica enhanced the tolerance of white clover in response to water stress by enhancing antioxidant enzyme activities and accelerating the ascorbate-glutathione cycle.

Global Integrated Genomic and Transcriptomic Analyses of MYB Transcription Factor Superfamily in C3 Model Plant Oryza sativa (L.) Unravel Potential Candidates Involved in Abiotic Stress Signaling.

Plant transcription factors (TFs) are significant players in transcriptional regulations, signal transduction, and constitute an integral part of signaling networks. MYB TFs are major TF superfamilies that play pivotal roles in regulation of transcriptional reprogramming, physiological processes, and abiotic stress (AbS) responses. To explore the understanding of MYB TFs, genome and transcriptome-wide identification was performed in the C3 model plant, Oryza sativa (OsMYB). This study retrieved 114 OsMYB TFs that were computationally analyzed for their expression profiling, gene organization, cis-acting elements, and physicochemical properties. Based on the microarray datasets, six OsMYB genes which were sorted out and identified by a differential expression pattern were noted in various tissues. Systematic expression profiling of OsMYB TFs showed their meta-differential expression of different AbS treatments, spatio-temporal gene expression of various tissues and their growth in the field, and gene expression profiling in responses to phytohormones. In addition, the circular ideogram of OsMYB genes in related C4 grass plants conferred the gene synteny. Protein-protein interactions of these genes revealed the molecular crosstalk of OsMYB TFs. Transcriptional analysis (qPCR) of six OsMYB players in response to drought and salinity stress suggested the involvement in individual and combined AbS responses. To decipher how these OsMYB play functional roles in AbS dynamics, further research is a prerequisite.

Elucidating the dialogue between arbuscular mycorrhizal fungi and polyamines in plants.

The most dominant arbuscular mycorrhizal (AM) symbiont can be established on roots of most terrestrial plants by beneficial AM fungi. A type of polycationic and aliphatic compounds, polyamines (PAs), are involved in plant physiological activities including stress responses. Interestingly, small amounts of PAs such as putrescine (Put) and spermidine (Spd) were found in AM fungal spores, and they are considered to be a component involved in mycorrhizal development, including mycorrhizal colonization, appressoria formation, spore germination and mycelial growth. Thus, PAs are regulatory factors in plant-AM symbiosis. Inoculation of AM fungi also affects the metabolism of endogenous PAs in host plants, including PAs synthesis and catabolism, thus, regulating various physiological events of the host. As a result, there seems to be a dialogue between PAs and AM fungi. Existing knowledge makes us understand that endogenous or exogenous PAs are an important regulator factor in the growth of AM fungi, as well as a key substance to colonize roots, which further enhances mycorrhizal benefits in plant growth responses and root architecture. The presence of AM symbiosis in roots alters the dynamic balance of endogenous PAs, triggering osmotic adjustment and antioxidant defense systems, maintaining charge balance and acting as a stress signalling molecule, which affects various physiological activities, such as plant growth, nutrient acquisition, stress tolerance and improvement of root architecture. This review mainly elucidated (i) what is the role of fungal endogenous PAs in fungal growth and colonization of roots in host plants? (ii) how AM fungi and PAs interact with each other to alter the growth of fungi and plants and subsequent activities, providing the reference for the future combined use of AM fungi and PAs in agricultural production, although there are still many unknown events in the dialogue.