Improved Root Architecture Research Articles

Effect of Trichoderma Culture Filtrates of as Inducer on Growth Parameters of Tomato (Solanum lycopersicum L.) against Fusarium Wilt

Aims: The present study was carried out to evaluate the effect of culture filtrates from different Trichoderma isolates at 10% concentration on the growth parameters of tomato plants over two growing seasons (2021-22 and 2022-23). Study Design: The experiment was performed both in vitro and in vivo condition, Completely Randomized Design (CRD) used for in vitro and Randomized Block Design (RBD) used for in vivo experiment Place and Duration of Study: The experiment was performed at Chandra Shekhar Azad University of Agriculture and Technology, Kanpur (India) during 2021-22 and 2022-23. Methodology: The soil sample collected from 12 different location of India and Trichoderma isolated and these different isolates used to produce their individual culture filtrate and these culture filtrates further use with 10% concentration as treatment for tomato plant. The effect of culture filtrates on plant height, root length, number of branches, fresh and dry shoot and root weight were observed under the experiment. Results: Results show significant improvements in plant height, root length, fresh and dry weights and number of branches in all culture filtrate treated plants involving T9 (seedling treatment + one foliar spray with culture filtrate of Trichoderma Nagaur), which consistently outperformed other isolates. Plant height increased to 43.06 cm in 2021-22 and 44.56 cm in 2022-23 at 40 days after transplanting with isolate T9 treatment followed by culture filtrate of Trichoderma Jabalpur (T7) and Trichoderma Banda (T6) showed 11.56, 22.96, 33.72, and 37.15 cm in 2021-22, and 11.38, 23.24, 34.46 and 36.08 cm for T6 in the same year. Among all the culture filtrates, the treatment T9 significantly enhances root length, fresh shoot and root weights and the number of branches. The plants treated with isolate T9 also exhibited an increase of 98.94% in root fresh weight and 42.31% in shoot weight. Conclusion: The findings confirm the growth-promoting potential of the T9 Trichoderma, attributed to mechanisms such as hormone production, enhanced nutrient uptake and improved root architecture. These results align with previous studies demonstrating the benefits of Trichoderma species in plant growth enhancement.

Overexpression of Auxin/Indole-3-Acetic Acid Gene TrIAA27 Enhances Biomass, Drought, and Salt Tolerance in Arabidopsis thaliana

White clover (Trifolium repens L.) is an important forage and aesthetic plant species, but it is susceptible to drought and heat stress. The phytohormone auxin regulates several aspects of plant development and alleviates the effects of drought stress in plants, including white clover, by involving auxin/indole acetic acid (Aux/IAA) family genes. However, Aux/IAA genes and the underlying mechanism of auxin-mediated drought response remain elusive in white clover. To extend our understanding of the multiple functions of Aux/IAAs, the current study described the characterization of a member of the Aux/IAA family TrIAA27 of white clover. TrIAA27 protein had conserved the Aux/IAA family domain and shared high sequence similarity with the IAA27 gene of a closely related species and Arabidopsis. Expression of TrIAA27 was upregulated in response to heavy metal, drought, salt, NO, Ca2+, H2O2, Spm, ABA, and IAA treatments, while downregulated under cold stress in the roots and leaves of white clover. TrIAA27 protein was localized in the nucleus. Constitutive overexpression of TrIAA27 in Arabidopsis thaliana led to enhanced hypocotyl length, root length, plant height, leaf length and width, and fresh and dry weights under optimal and stress conditions. There was Improved photosynthesis activity, chlorophyll content, survival rate, relative water content, endogenous catalase (CAT), and peroxidase (POD) concentration with a significantly lower electrolyte leakage percentage, malondialdehyde (MDA) content, and hydrogen peroxide (H2O2) concentration in overexpression lines compared to wild-type Arabidopsis under drought and salt stress conditions. Exposure to stress conditions resulted in relatively weaker roots and above-ground plant growth inhibition, enhanced endogenous levels of major antioxidant enzymes, which correlated well with lower lipid peroxidation, lower levels of reactive oxygen species, and reduced cell death in overexpression lines. The data of the current study demonstrated that TrIAA27 is involved in positively regulating plant growth and development and could be considered a potential target gene for further use, including the breeding of white clover for higher biomass with improved root architecture and tolerance to abiotic stress.

Synchrotron tomography of magnetoprimed soybean plant root system architecture grown in arsenic-polluted soil.

The present study evaluated the repercussions of magnetopriming on the root system architecture of soybean plants subjected to arsenic toxicity using synchrotron radiation source based micro-computed tomography (SR-µCT). This will be used evey where as abbreviation for the technique for three-dimensional imaging. Seeds of soybean were exposed to the static magnetic field (SMF) of strength (200 mT) for 1h prior to sowing. Magnetoprimed and non-primed seeds were grown for 1 month in a soil-sand mixture containing four different levels of sodium arsenate (0, 5, 10, and 50 mg As kg-1 soil). The results showed that arsenic adversely affects the root growth in non-primed plants by reducing their root length, root biomass, root hair, size and number of root nodules, where the damaging effect of As was observed maximum at higher concentrations (10 and 50 mg As kg-1 soil). However, a significant improvement in root morphology was detected in magnetoprimed plants where SMF pretreatment enhanced the root length, root biomass, pore diameter of cortical cells, root hair formation, lateral roots branching, and size of root nodules and girth of primary roots. Qualitative analysis of x-ray micro-CT images showed that arsenic toxicity damaged the epidermal and cortical layers of the root as well as reduced the pore diameter of the cortical cells. However, the diameter of cortical cells pores in magnetoprimed plants was observed higher as compared to plants emerged from non-primed seeds at all level of As toxicity. Thus, the study suggested that magnetopriming has the potential to attenuate the toxic effect of As and could be employed as a pre-sowing treatment to reduce the phytotoxic effects of metal ions in plants by improving root architecture and root tolerance index. This study is the very first exploration of the potential benefits of magnetopriming in mitigating the toxicity of metals (As) in plant roots utilizing the micro-CT technique.

Canola inoculation with Pseudomonas baetica R27N3 under salt stress condition improved antioxidant defense and increased expression of salt resistance elements

Inoculation with growth promoting rhizobacteria (PGPR) can lessen salt salinity injury in plants by improving some physiological, biochemical, and molecular aspects. The current study aims to investigate Pseudomonas baetica R27N3 on photosynthetic capacity, and the antioxidant defense system of salt-affected canola plants (0, 100, 200,300 mM NaCl) under greenhouse conditions. Sodium concentration in inoculated canola plants was significantly decreased, whilst potassium increased through improved root architecture and relative expression of ion pump genes, such as SOS1 and KAT1. Moreover, inoculated canola plants showed higher antioxidant capacity which was evident in their higher antioxidant enzyme activity and those enzymes' higher relative gene expression. The study investigated additional physiological parameters related to enhanced antioxidant defense, including the electrolyte leakage index and malondialdehyde concentration as indicators of the stability of the plant cell plasma membrane. The plasma membrane of canola plants treated with PGPR was significantly more stable than those without the PGPR treatment. Furthermore, carotenoids and proline accumulation as non-enzymatic antioxidant solutes and total protein were increased in canola plants treated with R27N3. On the whole, these improvements coincided with increased antioxidant capacity, but all these positive effects of R27N3 were notable under 100 mM of NaCl concentration, whereas under 0 and 300 mM of NaCl concentration physiological and molecular changes between inoculated and non-inoculated canola plants were not statistically notable. Consequently, positive molecular and biochemical changes could be mediated by P.baetica R27N3 ability to clone on canola root and provide it with a decent level of macro-nutrients.

DUF4057 containing express-protein negatively regulates the drought responses in rice

The current global climatic conditions project drought as a severe form of abiotic stress that directly impacts the agricultural productivity of economically important crops. In this study, we conducted a functional characterization of a drought-responsive express-protein (OsEP) that contains the DUF-4057 superfamily domain. In silico analysis revealed differential expression of the OsEP gene in two drought-responsive rice varieties with contrasting characteristics (Heena, drought-tolerant, and Kiran, drought-sensitive). According to phylogenetic analysis, OsEP showed a high amino acid identity with the protein of Panicum hallii and Zizania palustris. Following treatment with 20% PEG, quantitative real-time PCR demonstrated an increased abundance of OsEP gene transcripts. The OsEP gene exhibited the highest expression levels in the gynoecium and roots of the rice plant. Notably, rice lines over-expressing OsEP were found to be sensitive to PEG-induced drought stress, whereas knockdown lines exhibited improved root architecture and lignification of root cells, enabling them to withstand severe water deficit conditions. Furthermore, drought stress compromised the growth parameters and grain yield of OsEP over-expressing lines compared to knock-down lines. Increased activity of antioxidant enzymes such as CAT (catalase), APX (Ascorbate peroxidase), and SOD (Superoxide Dismutase) was observed in knock-down lines compared to both over-expressing lines and wild-type plants. Additionally, knock-down lines exhibited decreased levels of membrane stability marker (MDA) and electrolyte leakage, along with elevated proline content. Important regulatory genes such as OsHsfC1b, OsbZIP81, and OsNCED, positively impacted by osmotic/drought stress, exhibit variable expression in over-expressing and knock-down lines. These findings suggest that down-regulation of the OsEP gene modulates the genomic architecture of knock-down lines, allowing them to maintain cellular homeostasis by regulating enzymatic activity. Our results indicate that the OsEP gene is a negative regulator of drought response. Moreover, GA-JA (Gibberellic Acid-Jasmonic Acid) cross-talk is involved in the down-regulation of stress-related phenomena in over-expressing lines. Overall, this study sheds light on the crucial role of the DUF4057 superfamily gene in drought response and provides insights into its potential regulatory mechanism.

Comparative physiological, metabolomic, and transcriptomic analyses reveal mechanisms of apple dwarfing rootstock root morphogenesis under nitrogen and/or phosphorus deficient conditions.

Nitrogen (N) and phosphorus (P) are essential phytomacronutrients, and deficiencies in these two elements limit growth and yield in apple (Malus domestica Borkh.). The rootstock plays a key role in the nutrient uptake and environmental adaptation of apple. The objective of this study was to investigate the effects of N and/or P deficiency on hydroponically-grown dwarfing rootstock 'M9-T337' seedlings, particularly the roots, by performing an integrated physiological, transcriptomics-, and metabolomics-based analyses. Compared to N and P sufficiency, N and/or P deficiency inhibited aboveground growth, increased the partitioning of total N and total P in roots, enhanced the total number of tips, length, volume, and surface area of roots, and improved the root-to-shoot ratio. P and/or N deficiency inhibited influx into roots, and H+ pumps played a important role in the response to P and/or N deficiency. Conjoint analysis of differentially expressed genes and differentially accumulated metabolites in roots revealed that N and/or P deficiency altered the biosynthesis of cell wall components such as cellulose, hemicellulose, lignin, and pectin. The expression of MdEXPA4 and MdEXLB1, two cell wall expansin genes, were shown to be induced by N and/or P deficiency. Overexpression of MdEXPA4 enhanced root development and improved tolerance to N and/or P deficiency in transgenic Arabidopsis thaliana plants. In addition, overexpression of MdEXLB1 in transgenic Solanum lycopersicum seedlings increased the root surface area and promoted acquisition of N and P, thereby facilitating plant growth and adaptation to N and/or P deficiency. Collectively, these results provided a reference for improving root architecture in dwarfing rootstock and furthering our understanding of integration between N and P signaling pathways.

Bacillibactin siderophore induces iron mobilisation responses inside aerobic rice variety through YSL15 transporter

Iron uptake in Oryza sativa primarily occurs with the help of phytosiderophore i.e., deoxymugineic acid in aerobic condition. Internalisation of phytosiderophore-iron complex occurs through YSL15. However, aerobic rice at high pH faces iron deficit condition due to low secretion of plant siderophore and its early diminution. There might be a possibility that microbial siderophore of predominant rhizobacteria present in soil around rice may assist in iron uptake and transport through same transporter providing survival advantage to the plant. Present study aims to explore role of siderophore of Bacillus subtilis in improving root architecture and iron uptake in aerobic rice at high pH and explore possible transporters involved in transporting siderophore-Fe3+ complex inside rice root from rhizosphere. Identification by chrome azurol sulphonate assay and characterisation of purified extract from B. subtilis culture through LC-ESI MS confirmed presence of catecholate siderophore, Bacillibactin. Aerobic rice variety viz. Swarna Shreya grown with 5 ng/ml bacillibactin showed improved morphology and anatomy than untreated sample at alkaline pH 7.5. This is possibly due to enhanced intracellular iron content as observed in atomic absorption spectroscopy. Whole root proteomic analysis of rice root by using LC-ESI MS/MS revealed presence of YSL like transporter and siderophore import proteins in treated sample. RT-qPCR analysis showed enhanced expression of gene YSL15 in siderophore treated sample than control (pH 7.5). The present study possibly suggest role of foreign siderophore (xenosiderophore) in plant growth and development through iron uptake and transport inside rice.

Effects of arbuscular mycorrhizal fungus inoculation on the growth and nitrogen metabolism of Catalpa bungei C.A.Mey. under different nitrogen levels.

Evidence suggests that arbuscular mycorrhizal fungi (AMF) may promote the growth of woody plants. However, the effects of AMF on nitrogen (N) metabolism in plants, especially trees, and its regulatory mechanism are rarely reported. Here, the effects of AMF inoculation on the growth and N nutrition status of Catalpa bungei under different N levels were reported. Three N levels (low, medium, high) and two mycorrhizal inoculation treatments (inoculation with Rhizophagus intraradices or not) were used with factorial design. The results showed that medium N could significantly improve the physiological metabolism and growth of C. bungei seedlings. However, when N was excessive, growth was significantly inhibited whether inoculated AMF or not. Compared with non-inoculated treatments, AMF inoculation could promote the absorption of N and P, improve photosynthesis under low to medium N levels, thus promoting the growth of seedlings. AMF changed the biomass allocation in seedlings by reducing the stem mass ratio and root/shoot ratio, and increasing the leaf mass ratio. At medium N levels, compared with non-inoculated treatment, AMF inoculation could significantly promote root growth by changing root hormone levels and improving root architecture and root activity. Under N addition, AMF inoculation could improve the absorption and assimilation of N by regulating the expression of key enzyme genes of N metabolism and nitrate transporter genes (NRT2.4, NRT2.5, NRT2.7) in roots, and enhancing the activities of the key enzyme of N metabolism. This study may provide a reference for the application of AMF in the cultivation and afforestation technology of C. bungei in Northwest China.

Integrated Metabolomics and Morpho-Biochemical Analyses Reveal a Better Performance of Azospirillum brasilense over Plant-Derived Biostimulants in Counteracting Salt Stress in Tomato.

Increased soil salinity is one of the main concerns in agriculture and food production, and it negatively affects plant growth and crop productivity. In order to mitigate the adverse effects of salinity stress, plant biostimulants (PBs) have been indicated as a promising approach. Indeed, these products have a beneficial effect on plants by acting on primary and secondary metabolism and by inducing the accumulation of protective molecules against oxidative stress. In this context, the present work is aimed at comparatively investigating the effects of microbial (i.e., Azospirillum brasilense) and plant-derived biostimulants in alleviating salt stress in tomato plants by adopting a multidisciplinary approach. To do so, the morphological and biochemical effects were assessed by analyzing the biomass accumulation and root characteristics, the activity of antioxidant enzymes and osmotic stress protection. Furthermore, modifications in the metabolomic profiles of both leaves and root exudates were also investigated by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOF-MS). According to the results, biomass accumulation decreased under high salinity. However, the treatment with A. brasilense considerably improved root architecture and increased root biomass by 156% and 118% in non-saline and saline conditions, respectively. The antioxidant enzymes and proline production were enhanced in salinity stress at different levels according to the biostimulant applied. Moreover, the metabolomic analyses pointed out a wide set of processes being affected by salinity and biostimulant interactions. Crucial compounds belonging to secondary metabolism (phenylpropanoids, alkaloids and other N-containing metabolites, and membrane lipids) and phytohormones (brassinosteroids, cytokinins and methylsalicylate) showed the most pronounced modulation. Overall, our results suggest a better performance of A. brasilense in alleviating high salinity than the vegetal-derived protein hydrolysates herein evaluated.

Characterization and selection of endophytic actinobacteria for growth and disease management of Tea (Camellia sinensis L.).

Endophytic microbes are vital for nutrient solubilization and uptake, growth, and survival of plants. Here, 88 endophytic actinobacteria (EnA) associated with five tea clones were isolated, assessed for their diversity, plant growth promoting (PGP), and biocontrol traits, and then used as an inoculant for PGP and disease control in host and non-host plants. Polyphasic methods, including phenotypic and genotypic characteristics led to their identification as Streptomyces, Microbacterium, Curtobacterium, Janibacter, Rhodococcus, Nocardia, Gordonia, Nocardiopsis, and Kribbella. Out of 88 isolates, 35 (39.77%) showed antagonistic activity in vitro against major fungal pathogens, viz. Fusarium oxysporum, Rhizoctonia solani, Exobasidium vexans, Poria hypobrunnea, Phellinus lamaensis, and Nigrospora sphaerica. Regarding PGP activities, the percentage of isolates that produced indole acetic acid, siderophore, and ammonia, as well as P-solubilisation and nitrogen fixation, were 67.05, 75, 80.68, 27.27, 57.95, respectively. A total of 51 and 42 isolates showed chitinase and 1-aminocyclopropane-1-carboxylic acid deaminase activity, respectively. Further, two potent Streptomyces strains KA12 and MA34, selected based on the bonitur scale, were screened for biofilm formation ability and tested in vivo under nursery conditions. Confocal laser scanning microscopy and the crystal violet staining technique revealed that these Streptomyces strains can form biofilms, indicating the potential for plant colonization. In the nursery experiment, they significantly enhanced the shoot and root biomass, shoot and root length, and leaf number in host tea plants. Additionally, treatment of tomato seeds by KA12 suppressed the growth of fungal pathogen Fusarium oxysporum, increased seed germination, and improved root architecture, demonstrating its ability to be used as a seed biopriming agent. Our results confirm the potential of tea endophytic actinobacterial strains with multifarious beneficial traits to enhance plant growth and suppress fungal pathogens, which may be used as bioinoculant for sustainable agriculture.

Inter-Genera Colonization of Ocimum tenuiflorum Endophytes in Tomato and Their Complementary Effects on Na+/K+ Balance, Oxidative Stress Regulation, and Root Architecture Under Elevated Soil Salinity.

Endophytic bacilli of ethano-botanical plant Ocimum tenuiflorum were screened for salt stress-alleviating traits in tomato. Four promising O. tenuiflorum endophytes (Bacillus safensis BTL5, Bacillus haynesii GTR8, Bacillus paralicheniformis GTR11, and Bacillus altitudinis GTS16) were used in this study. Confocal scanning laser microscopic studies revealed the inter-genera colonization of O. tenuiflorum endophytes in tomato plants, giving insights for widening the applicability of potential endophytes to other crops. Furthermore, in a pot trial under 150 mM NaCl concentration, the inoculated endophytes contributed in reducing salt toxicity and improving recovery from salt-induced oxidative stress by different mechanisms. Reduction in reactive oxygen species (ROS) (sub-cellular H2O2 and superoxide) accumulation was observed besides lowering programmed cell death and increasing chlorophyll content. Endophyte inoculation supplemented the plant antioxidant enzyme system via the modulation of enzymatic antioxidants, viz., peroxidase, ascorbate peroxidase, superoxide dismutase, and catalase, apart from increasing proline and total phenolics. Antioxidants like proline have dual roles of antioxidants and osmoregulation, which might also have contributed to improved water relation under elevated salinity. Root architecture, viz., root length, projection area, surface area, average diameter, tips, forks, crossings, and the number of links, was improved upon inoculation, indicating healthy root growth and enhanced nutrient flow and water homeostasis. Regulation of Na+/K+ balance and water homeostasis in the plants were also evident from the modulation in the expression of abiotic stress-responsive genes, viz., LKT1, NHX1, SOS1, LePIP2, SlERF16, and SlWRKY39. Shoot tissues staining with light-excitable Na+ indicator Sodium GreenTM Tetra (tetramethylammonium) salt showed low sodium transport and accumulation in endophyte-inoculated plants. All four endophytes exhibited different mechanisms for stress alleviation and indicated complementary effects on plant growth. Furthermore, this could be harnessed in the form of a consortium for salt stress alleviation. The present study established inter-genera colonization of O. tenuiflorum endophytes in tomato and revealed its potential in maintaining Na+/K+ balance, reducing ROS, and improving root architecture under elevated salinity.

Genetics components of rice root architecture and carbon isotopic fractionation parameters: a tracer for breeding in a water-saving irrigation management

Phenotyping is the major bottleneck in the effort to develop varieties of rice (Oryza sativa L.) suitable for growing under a water-saving irrigation management, such as alternate wetting and drying irrigation techniques (AWD). To analyze if the genotypic variability for carbon isotope discrimination (CID) in rice leaves could be used as a relatively high-throughput tracer to early select superior genotypes highlighting improved root architecture traits when submitted to AWD, a set of twenty varieties grown under semi-natural conditions were submitted to two water irrigation regimes, continuous flooding (CF) and AWD cycles. Coefficients of genetic variance (π2g) obtained for root architecture, micro-morphological and physiological traits were significant for all of them regardless of the adopted irrigation system, except to mean root diameter. The three significant principal components (PCs) with eigenvalue > 1, explain most of the total variation across cycles and water regimes. For most of analyzed traits, the values of heritability coefficients were higher regardless of adopted irrigation management and trait category; for CID, the magnitudes of broad heritability at an individual level (greater than 0.80) were similar in the two irrigation techniques, evidencing that the success of the selection is independent of irrigation management. The higher CID values after three AWD cycles are associated with varieties with higher total root length and volume. To our knowledge, this is the first study demonstrating the potential application of CID as a tracer to select root architecture traits in rice when water-saving irrigation management is of concern.

Insights into the Interactions among Roots, Rhizosphere, and Rhizobacteria for Improving Plant Growth and Tolerance to Abiotic Stresses: A Review.

Abiotic stresses, such as drought, salinity, heavy metals, variations in temperature, and ultraviolet (UV) radiation, are antagonistic to plant growth and development, resulting in an overall decrease in plant yield. These stresses have direct effects on the rhizosphere, thus severely affect the root growth, and thereby affecting the overall plant growth, health, and productivity. However, the growth-promoting rhizobacteria that colonize the rhizosphere/endorhizosphere protect the roots from the adverse effects of abiotic stress and facilitate plant growth by various direct and indirect mechanisms. In the rhizosphere, plants are constantly interacting with thousands of these microorganisms, yet it is not very clear when and how these complex root, rhizosphere, and rhizobacteria interactions occur under abiotic stresses. Therefore, the present review attempts to focus on root–rhizosphere and rhizobacterial interactions under stresses, how roots respond to these interactions, and the role of rhizobacteria under these stresses. Further, the review focuses on the underlying mechanisms employed by rhizobacteria for improving root architecture and plant tolerance to abiotic stresses.

Melatonin Mitigates Nickel Toxicity by Improving Nutrient Uptake Fluxes, Root Architecture System, Photosynthesis, and Antioxidant Potential in Tomato Seedling

Globally, crop production has been widely threatened by contamination of arable lands with heavy metals including Nickel (Ni). Stress-relief molecule melatonin (ME) has been widely used to mitigate the phytotoxicity induced by heavy metals. The current study aimed to explore the response to Ni stress and the alleviating role of ME in boosting Ni-stress tolerance in tomato seedlings. The roots of tomato seedlings pretreated with ME (100 μM) for 3 days, followed by applied Ni (50 μM) for 7 days. The treatments were composed of (1) control (CK); (2) melatonin (ME, 100 μM); (3) nickel (Ni, 50 μM); and (4) melatonin and nickel treatment (ME+Ni, 100 μM + 50 μM). Nickel toxicity noticeably inhibited plant growth and biomass production by impairing the root architecture, photosynthesis process, nutrient uptake, and antioxidant enzymes. Conversely, ME-supplementation inhibited Ni-induced growth damage, improved root architecture, nutrient uptake, pigment contents, and leaf gas exchange parameters, and decreased Ni-accumulation. Furthermore, the electrolyte leakage (EL), malondialdehyde (MDA) content, and reactive oxygen species (ROS) accumulation were significantly reduced in ME-treated seedlings via improving antioxidant enzyme activity as well as upregulation of their encoding gene expression. In conclusion, our findings provide a shred of substantial evidence that ME improved Ni-induced phytotoxicity in tomato seedlings, mainly by improving the root architecture, biomass production, mineral homeostasis (reducing nickel accumulation in plants), and photosynthetic efficiency.

Mycorrhizal fungi enhance flooding tolerance of peach through inducing proline accumulation and improving root architecture

This study aimed to evaluate the effect of an arbuscular mycorrhizal fungus (AMF) Glomus mosseae on plant growth, root architecture, and proline metabolism in roots of peach (Prunes persica L.) under non-flooding and flooding conditions. The 12-day flooding dramatically inhibited root colonisation of G. mosseae, but induced a large number of extraradical mycelia. Although the flooding treatment also relatively inhibited growth and root architecture of peach, the mycorrhizal fungal inoculation dramatically increased shoot and root biomass, plant height, stem diameter, number of 1<sup>st</sup>- and 2<sup>nd</sup>-order lateral roots, root total length (mainly 0–1 cm and > 3 cm long), root surface area, and root volume under flooding. The study also revealed distinctly higher proline accumulation in the roots of mycorrhizal plants than non-mycorrhizal plants under both non-flooding and flooding conditions, accompanied by higher Δ<sup>1</sup>-pyrroline-5-carboxylate synthase (P5CS) activity and lower δ-ornithine transaminase and proline dehydrogenase activities. In addition, the PpP5CS1 gene expression was up-regulated by flooding and mycorrhization. This study concluded that mycorrhizal fungi enhanced flooding tolerance of peach through inducing proline accumulation and improving root architecture.

Enrichment of Organic Manure with Plant Growth Promoting Rhizobacteria Improved the Root and Shoot Growth of Okra (Abelmoschus esculentus L. Moench.)

A well-structured root system is essential to ensure optimal plant growth and yield. Two experiments were conducted to determine the effects of plant growth promoting rhizobacteria (PGPR) on the root system of okra plant. These experiments were arranged with a completely randomized design. The first experiment was conducted in the growth chamber with 8 different bacterial isolates consisting of Methylobacterium sp., Bacillus sp., Bacillus methylotrophicus, Flavobacterium tirrenicum, Providencia stuartii, Azotobacter vinelandii, Methylocystis parvus and PGPR consortium. The second experiment was conducted in the greenhouse and examined the effects of four poultry manure rates, i.e. 0, 6, 12 and 18 ton ha-1, or equivalent to 0, 75, 150 and 225% of recommended rates and how these are altered with the presence or absence of PGPR. The results of the experiments showed that, PGPR significantly improved root architecture; the number and length of lateral roots was increased by 242.86% and 777.79% respectively, as well as the dry weight of the roots and shoots of okra plant by 236.36% and 333.33%, respectively. Moreover applying 150% (12 t.ha-1) of the recommended rate of poultry manure enriched with PGPR was found to be most effective in terms of improving the growth and root attributes of okra plants.

Fine mapping and candidate gene analysis of qRN5a, a novel QTL promoting root number in rice under low potassium.

KEY MESSAGE: qRN5a, a novel QTL for increasing root number under low K in rice, was fine mapped to a 48.8-kb region on chromosome 5, and LOC_Os05g27980 is the most likely candidate gene. Potassium (K) is a mineral nutrient essential for plant growth and development, but the molecular mechanism for low-K (LK) tolerance in rice remains poorly understood. In our previous study, the quantitative trait locus (QTL) qRN5a for root number (RN) under LK was identified in the chromosome segment substitution line CSSL35 carrying segments from XieqingzaoB in the genetic background of Zhonghui9308 (ZH9308). CSSL35 developed more roots than ZH9308 under LK at the seedling stage, and qRN5a was initially located within a 1,023-kb genomic region. In this study, to understand the molecular basis of qRN5a, a large F2:3 (BC5F2:3) population obtained from crossing CSSL35 and ZH9308 was constructed for fine mapping. High-resolution linkage analysis narrowed down qRN5a to a 48.8-kb interval flanked by markers A99 and A139. Seven putative candidate genes were annotated in the delimited region, and three genes (Os05g0346700, LOC_Os05g27980, and LOC_Os05g28000) had nonsynonymous single-nucleotide polymorphisms in the coding sequence between the two parents. Expression analysis suggests that LOC_Os05g27980, which encodes a LATERAL ORGAN BOUNDARIES domain-containing protein, is a positive regulator of RN under LK and is the most likely candidate gene for qRN5a. Moreover, we found that qRN5a promotes expression of OsIAA23 and represses OsHAK5 expression in root tissues to promote root initiation in CSSL35 under LK conditions. Additional investigations on OsHAK5 in rice are needed to elucidate the basis of changing root architecture under different K+ concentrations. qRN5a is useful for marker-assisted selection to develop an ideotype with improved root architecture in rice under K deficiency.

Overexpression of the NMig1 Gene Encoding a NudC Domain Protein Enhances Root Growth and Abiotic Stress Tolerance in Arabidopsis thaliana.

The family of NudC proteins has representatives in all eukaryotes and plays essential evolutionarily conserved roles in many aspects of organismal development and stress response, including nuclear migration, cell division, folding and stabilization of other proteins. This study investigates an undescribed Arabidopsis homolog of the Aspergillus nidulans NudC gene, named NMig1 (for Nuclear Migration 1), which shares high sequence similarity to other plant and mammalian NudC-like genes. Expression of NMig1 was highly upregulated in response to several abiotic stress factors, such as heat shock, drought and high salinity. Constitutive overexpression of NMig1 led to enhanced root growth and lateral root development under optimal and stress conditions. Exposure to abiotic stress resulted in relatively weaker inhibition of root length and branching in NMig1-overexpressing plants, compared to the wild-type Col-0. The expression level of antioxidant enzyme-encoding genes and other stress-associated genes was considerably induced in the transgenic plants. The increased expression of the major antioxidant enzymes and greater antioxidant potential correlated well with the lower levels of reactive oxygen species (ROS) and lower lipid peroxidation. In addition, the overexpression of NMig1 was associated with strong upregulation of genes encoding heat shock proteins and abiotic stress-associated genes. Therefore, our data demonstrate that the NudC homolog NMig1 could be considered as a potentially important target gene for further use, including breeding more resilient crops with improved root architecture under abiotic stress.

Arabidopsis thaliana trehalose-6-phosphate phosphatase gene TPPI enhances drought tolerance by regulating stomatal apertures.

Transpiration occurs through stomata. The alteration of stomatal apertures in response to drought stress is an important process associated with water use efficiency (WUE). Trehalose-6-phosphate phosphatase (TPP) family genes have been reported to participate in adjustment of stomatal aperture. However, there have been no reports of the trehalose metabolism pathway genes improving WUE, and the upstream signalling pathway modulating these genes is not clear. Here, we demonstrate that a member of the TPP gene family, AtTPPI, confers drought resistance and improves WUE by decreasing stomatal apertures and improving root architecture. The reduced expression of AtTPPI caused a drought-sensitive phenotype, while its overexpression significantly increased drought tolerance. Abscisic acid (ABA)-induced stomatal closure experiments confirmed that AtTPPI mutation increased the stomatal aperture compared with that of wild-type plants; in contrast, overexpression plants had smaller stomatal apertures than those of wild-type plants. Moreover, AtTPPI mutation also caused stunted primary root length and compromised auxin transport, while overexpression plants had longer primary root lengths. Yeast one-hybrid assays showed that ABA-responsive element-binding factor1 (ABF1), ABF2, and ABF4 directly regulated AtTPPI expression. In summary, the way in which AtTPPI responds to drought stress suggests that AtTPPI-mediated stomatal regulation is an important mechanism to cope with drought stress and improve WUE.

Optimizing root architecture and increasing transporter gene expression are strategies to promote selenium uptake by high-se accumulating rice cultivar

Selenium uptake capacity can vary among rice genotypes; however, the processes driving these high- and low-Se-accumulating rice cultivars have not yet been defined. The root architecture, selenium uptake, and transporter genes (Sultr2;1 and Ospt2) and selenium-binding protein (SBP1) expression of high- and low-Se rice cultivars were determined in agar culture experiment with different selenite and selenate concentrations. Root architecture analysis showed that the toxicity of selenite was greater than that of selenate for both rice cultivars, and the Se tolerance of the high-Se rice for selenite was greater than that of the low-Se rice. The uptake rate of selenite was greater than that of selenate, and the high-Se rice accumulated a higher Se concentration in the roots. However, selenite translocation via the xylem was limited, and the two rice cultivars accumulated similar amounts of Se in shoots when it was supplied as selenite. By contrast, selenate was highly mobile via xylem transport, and the high-Se rice accumulated a higher Se concentration in the shoots when it was supplied. The transcript levels of the Sultr2;1 and Ospt2 genes were higher in the high-Se rice than in the low-Se rice with selenite or selenate application. The application of selenite or selenate increased the SBP1 transcript level in the high-Se rice but decreased the transcript level of SBP1 in the low-Se rice. The increased expression of phosphate and sulfate transporters and improved root architecture may explain how the high-Se rice cultivar can take up more selenite and selenate, respectively.