Inhibition Of Primary Root Growth Research Articles

Transcription factor WOX11 modulates tolerance to cyst nematodes via adventitious lateral root formation.

The transcription factor WUSCHEL-RELATED HOMEOBOX 11 (WOX11) in Arabidopsis (Arabidopsis thaliana) initiates the formation of adventitious lateral roots upon mechanical injury in primary roots. Root-invading nematodes also induce de novo root organogenesis leading to excessive root branching, but it is not known if this symptom of disease involves mediation by WOX11 and if it benefits the plant. Here, we show with targeted transcriptional repression and reporter gene analyses in Arabidopsis that the beet cyst nematode Heterodera schachtii activates WOX11-mediated adventitious lateral rooting from primary roots close to infection sites. The activation of WOX11 in nematode-infected roots occurs downstream of jasmonic acid-dependent damage signaling via ETHYLENE RESPONSE FACTOR109, linking adventitious lateral root formation to nematode damage to host tissues. By measuring different root system components, we found that WOX11-mediated formation of adventitious lateral roots compensates for nematode-induced inhibition of primary root growth. Our observations further demonstrate that WOX11-mediated rooting reduces the impact of nematode infections on aboveground plant development and growth. Altogether, we conclude that the transcriptional regulation by WOX11 modulates root system plasticity under biotic stress, which is one of the key mechanisms underlying the tolerance of Arabidopsis to cyst nematode infections.

Control of lateral root formation by rapamycin-induced dimerization of engineered RGI/BAK1 and by BIR3 chimera.

Leucine-rich repeat receptor kinases (LRR-RKs) play a pivotal role in diverse aspects of growth, development, and immunity in plants by sensing extracellular signals. Typically, LRR-RKs are activated through the ligand-induced interaction with a SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) coreceptor, triggering downstream signaling. ROOT MERISTEM GROWTH FACTOR1 (RGF1) INSENSITIVEs (RGIs) LRR-RLK receptors promote primary root meristem activity while inhibiting lateral root (LR) development in response to RGF peptide. In this study, we employed rapamycin-induced dimerization (RiD) and BAK1-INTERACTING RECEPTOR-LIKE KINASE3 (BIR3) chimera approaches to explore the gain-of-function of RGI1, RGI4, and RGI5. Rapamycin induced the association of cytosolic kinase domains (CKDs) of RGI1 and the BAK1 coreceptor, activating both mitogen-activated protein kinase 3 (MPK3) and MPK6. Rapamycin significantly inhibited LR formation in RiD-RGI1/RGI4/RGI5-BAK1 plants. Using transgenic Arabidopsis expressing RGI1CKD fused to the BIR3-LRR chimera under estradiol control, we observed a substantial reduction in LR density upon β-estradiol treatment. Additionally, we identified a decrease in root gravitropism in BIR3 chimera plants. In contrast, RiD-RGI/BAK1 plants did not exhibit defects in root gravitropism, implying the importance of combinatorial interactions between RGIs and SERK coreceptors in the inhibition of root gravitropism. Constitutive activation of RGIs with BAK1 in RiD-RGI/BAK1 plants by rapamycin treatment resulted in the inhibition of primary root growth, resembling the inhibitory effects observed with high concentrations of phytohormones on primary root elongation. Our findings highlight that the interactions between CKDs of RGIs and BAK1, constitutively induced by rapamycin or BIR3 chimera, efficiently control LR development.

A novel PGPR strain homologous to Beijerinckia fluminensis induces biochemical and molecular changes involved in Arabidopsis thaliana salt tolerance

The use of PGPR is widely accepted as a promising tool for a more sustainable agricultural production and improved plant abiotic stress resistance. This study tested the ability of PVr_9, a novel bacterial strain, homologous to Beijerinckia fluminensis, to increase salt stress tolerance in A. thaliana. In vitro plantlets inoculated with PVr_9 and treated with 150 mM NaCl showed a reduction in primary root growth inhibition compared to uninoculated ones, and a leaf area significantly less affected by salt. Furthermore, salt-stressed PVr_9-inoculated plants had low ROS and 8-oxo-dG, osmolytes, and ABA content along with a modulation in antioxidant enzymatic activities. A significant decrease in Na+ in the leaves and a corresponding increase in the roots were also observed in salt-stressed inoculated plants. SOS1, NHX1 genes involved in plant salt tolerance, were up-regulated in PVr_9-inoculated plants, while different MYB genes involved in salt stress signal response were down-regulated in both roots and shoots. Thus, PVr_9 was able to increase salt tolerance in A. thaliana, thereby suggesting a role in ion homeostasis by reducing salt stress rather than inhibiting total Na+ uptake. These results showed a possible molecular mechanism of crosstalk between PVr_9 and plant roots to enhance salt tolerance, and highlighted this bacterium as a promising PGPR for field applications on agronomical crops.

Protein kinase SnRK2.4 is a key regulator of aquaporins and root hydraulics in Arabidopsis.

Soil water uptake by roots is a key component of plant water homeostasis contributing to plant growth and survival under ever-changing environmental conditions. The water transport capacity of roots (root hydraulic conductivity; Lpr ) is mostly contributed by finely regulated Plasma membrane Intrinsic Protein (PIP) aquaporins. In this study, we used natural variation of Arabidopsis for the identification of quantitative trait loci (QTLs) contributing to Lpr . Using recombinant lines from a biparental cross (Cvi-0 x Col-0), we show that the gene encoding class 2 Sucrose-Non-Fermenting Protein kinase 2.4 (SnRK2.4) in Col-0 contributes to >30% of Lpr by enhancing aquaporin-dependent water transport. At variance with the inactive and possibly unstable Cvi-0 SnRK2.4 form, the Col-0 form interacts with and phosphorylates the prototypal PIP2;1 aquaporin at Ser121 and stimulates its water transport activity upon coexpression in Xenopus oocytes and yeast cells. Activation of PIP2;1 by Col-0 SnRK2.4 in yeast also requires its protein kinase activity and can be counteracted by clade A Protein Phosphatases 2C. SnRK2.4 shows all hallmarks to be part of core abscisic acid (ABA) signaling modules. Yet, long-term (>3 h) inhibition of Lpr by ABA possibly involves a SnRK2.4-independent inhibition of PIP2;1. SnRK2.4 also promotes stomatal aperture and ABA-induced inhibition of primary root growth. The study identifies a key component of Lpr and sheds new light on the functional overlap and specificity of SnRK2.4 with respect to other ABA-dependent or independent SnRK2s.

L-DOPA induces iron accumulation in roots of Ipomoea aquatica and Arabidopsis thaliana in a pH-dependent manner

BackgroundIron deficiency is the leading cause of anemia worldwide, particularly in countries with predominant plant-based diets. Plants constitute the main source of dietary iron. Increasing their iron concentration could reduce the occurrence of anemia. The water spinach Ipomoea aquatica is consumed as a vegetable throughout Asia and tolerates high iron concentrations making it an attractive candidate for iron biofortification. L-DOPA is an allelopathic molecule secreted by some legumes. L-DOPA can trigger the expression of Fe deficiency-inducible genes, and could potentially be used as a biostimulant to increase Fe concentration.ResultsL-DOPA significantly affected root growth of water spinach, and triggered a massive accumulation of Fe in roots. Both effects were exacerbated when L-DOPA was dissolved in KOH, which is surprising given that L-DOPA is less stable at high pH. To check whether a higher pH could indeed increase the bioactivity of L-DOPA, we used Arabidopsis thaliana, which grows at lower pH than water spinach, and subjected the plants to L-DOPA treatments at pH 5.5 and pH 6.0, which are both within the optimal range for Arabidopsis nutrition. At pH 6.0, the root growth of Arabidopsis was more strongly inhibited than at pH 5.5. We found that at higher pH, L-DOPA oxidizes to form a melanin precipitate.ConclusionsWe concluded that the oxidation of L-DOPA that we observed upon solubilization in KOH, or in nutrient solutions at slightly higher pH produces melanin-related molecules that are more potent than L-DOPA itself to trigger the primary root growth inhibition, Fe uptake and root Fe accumulation in water spinach and Arabidopsis.

Wheat type one protein phosphatase promotes salt and osmotic stress tolerance in arabidopsis via auxin-mediated remodelling of the root system

The control of optimal root growth and plant stress responses depends largely on a variety of phytohormones among which auxin and brassinosteroids (BRs) are the most influential. We have previously reported that the durum wheat type 1 protein phosphatase TdPP1 participates in the control of root growth by modulating BR signaling. In this study, we pursue our understanding of how TdPP1 fulfills this regulatory function on root growth by evaluating the physiological and molecular responses of Arabidopsis TdPP1 over-expressing lines to abiotic stresses. Our results showed that when exposed to 300 mM Mannitol or 100 mM NaCl, the seedlings of TdPP1 over-expressors exhibit modified root architecture with higher lateral root density, and longer root hairs concomitant with a lower inhibition of the primary root growth. These lines also exhibit faster gravitropic response and a decrease in primary root growth inhibition when exposed to high concentrations of exogenous IAA. On another hand, a cross between TdPP1 overexpressors and DR5:GUS marker line was performed to monitor auxin accumulation in roots. Remarkably, the TdPP1 overexpression resulted in an enhanced auxin gradient under salt stress with a higher accumulation in primary and lateral root tips. Moreover, TdPP1 transgenics exhibit a significant induction of a subset of auxin-responsive genes under salt stress conditions. Therefore, our results reveal a role of PP1 in enhancing auxin signaling to help shape greater root plasticity thus improving plant stress resilience.

Endogenous Serotonin Accumulation Coincides with Reorganization of Auxin Efflux Protein (PIN1) and Actin (ACT8) Accompanying Primary Root Growth Inhibition in NaCl-Stress-Induced Etiolated Sunflower (Helianthus annuus; cv. KBSH 44) Seedlings

Endogenous Serotonin Accumulation Coincides with Reorganization of Auxin Efflux Protein (PIN1) and Actin (ACT8) Accompanying Primary Root Growth Inhibition in NaCl-Stress-Induced Etiolated Sunflower (Helianthus annuus; cv. KBSH 44) Seedlings

OsLPR5 Encoding Ferroxidase Positively Regulates the Tolerance to Salt Stress in Rice.

Salinity is a major abiotic stress that harms rice growth and productivity. Low phosphate roots (LPRs) play a central role in Pi deficiency-mediated inhibition of primary root growth and have ferroxidase activity. However, the function of LPRs in salt stress response and tolerance in plants remains largely unknown. Here, we reported that the OsLPR5 was induced by NaCl stress and positively regulates the tolerance to salt stress in rice. Under NaCl stress, overexpression of OsLPR5 led to increased ferroxidase activity, more green leaves, higher levels of chlorophyll and lower MDA contents compared with the WT. In addition, OsLPR5 could promote the accumulation of cell osmotic adjustment substances and promote ROS-scavenging enzyme activities. Conversely, the mutant lpr5 had a lower ferroxidase activity and suffered severe damage under salt stress. Moreover, knock out of OsLPR5 caused excessive Na+ levels and Na+/K+ ratios. Taken together, our results exemplify a new molecular link between ferroxidase and salt stress tolerance in rice.

Brassinosteroid signaling regulates phosphate starvation-induced malate secretion in plants.

Inorganic phosphate (Pi) is often limited in soils due to precipitation with iron (Fe) and aluminum (Al). To scavenge heterogeneously distributed phosphorus (P) resources, plants have evolved a local Pi signaling pathway that induces malate secretion to solubilize the occluded Fe-P or Al-P oxides. In this study, we show that Pi limitation impaired brassinosteroid signaling and downregulated BRASSINAZOLE-RESISTANT 1 (BZR1) expression in Arabidopsis thaliana. Exogenous 2,4-epibrassinolide treatment or constitutive activation of BZR1 (in the bzr1-D mutant) significantly reduced primary root growth inhibition under Pi-starvation conditions by downregulating ALUMINUM-ACTIVATED MALATE TRANSPORTER 1 (ALMT1) expression and malate secretion. Furthermore, AtBZR1 competitively suppressed the activator effect of SENSITIVITY TO PROTON RHIZOTOXICITY 1 (STOP1) on ALMT1 expression and malate secretion in Nicotiana benthamiana leaves and Arabidopsis. The ratio of nuclear-localized STOP1 and BZR1 determined ALMT1 expression and malate secretion in Arabidopsis. In addition, BZR1-inhibited malate secretion is conserved in rice (Oryza sativa). Our findings provide insight into plant mechanisms for optimizing the secretion of malate, an important carbon resource, to adapt to Pi-deficiency stress.

PLDδ, auxin, and H2O2 mediated the allelopathic effect of cycloastragenol on root growth in Arabidopsis

Cycloastragenol (CAG) is a tetra-cyclic triterpenoid allelochemical. It has been widely studied in animals but rarely in plants. Here, we reported that a model allelochemical CAG inhibited primary root elongation of Arabidopsis by reducing the sizes of both the meristem and elongation zones. Phospholipase Dδ(PLDδ), hydrogen peroxide (H2O2), and auxin affected this process. After treatment with CAG, the expression of PLDδ and the activity of the Phospholipase D(PLD) enzyme increased in WT. Mutants analysis demonstrated that PLDδ negatively regulated the primary root elongation by CAG treatment. CAG treatment stimulated the accumulation of H2O2 in roots. The production of H2O2 was derived from cell wall peroxidase. Mutants analysis showed that PLDδ positively regulated the production of H2O2 by CAG treatment. CAG also decreased auxin content in the root tip by affecting the expression of auxin synthesis-related genes. PLDδ was involved in the auxin reduction mediated by CAG, but H2O2 did not participate in this process. In conclusion, PLDδ, auxin, and H2O2 mediated the inhibition of primary root growth by CAG in Arabidopsis.

Endoplasmic reticulum calnexins participate in the primary root growth response to phosphate deficiency.

Accumulation of incompletely folded proteins in the endoplasmic reticulum (ER) leads to ER stress, activates ER protein degradation pathways, and upregulates genes involved in protein folding. This process is known as the unfolded protein response (UPR). The role of ER protein folding in plant responses to nutrient deficiencies is unclear. We analyzed Arabidopsis (Arabidopsis thaliana) mutants affected in ER protein quality control and established that both CALNEXIN (CNX) genes function in the primary root response to phosphate (Pi) deficiency. CNX1 and CNX2 are homologous ER lectins promoting protein folding of N-glycosylated proteins via the recognition of the GlcMan9GlcNAc2 glycan. Growth of cnx1-1 and cnx2-2 single mutants was similar to that of the wild type under high and low Pi conditions, but the cnx1-1 cnx2-2 double mutant showed decreased primary root growth under low Pi conditions due to reduced meristematic cell division. This phenotype was specific to Pi deficiency; the double mutant responded normally to osmotic and salt stress. Expression of CNX2 mutated in amino acids involved in binding the GlcMan9GlcNAc2 glycan failed to complement the cnx1-1 cnx2-2 mutant. The root growth phenotype was Fe-dependent and was associated with root apoplastic Fe accumulation. Two genes involved in Fe-dependent inhibition of primary root growth under Pi deficiency, the ferroxidase LOW PHOSPHATE 1 (LPR1) and P5-type ATPase PLEIOTROPIC DRUG RESISTANCE 2 (PDR2) were epistatic to CNX1/CNX2. Overexpressing PDR2 failed to complement the cnx1-1 cnx2-2 root phenotype. The cnx1-1 cnx2-2 mutant showed no evidence of UPR activation, indicating a limited effect on ER protein folding. CNX might process a set of N-glycosylated proteins specifically involved in the response to Pi deficiency.

The Arabidopsis transcription factor TCP9 modulates root architectural plasticity, reactive oxygen species-mediated processes, and tolerance to cyst nematode infections.

Infections by root-feeding nematodes have profound effects on root system architecture and consequently shoot growth of host plants. Plants harbor intraspecific variation in their growth responses to belowground biotic stresses by nematodes, but the underlying mechanisms are not well understood. Here, we show that the transcription factor TEOSINTE BRANCHED/CYCLOIDEA/PROLIFERATING CELL FACTOR-9 (TCP9) modulates root system architectural plasticity in Arabidopsis thaliana in response to infections by the endoparasitic cyst nematode Heterodera schachtii. Young seedlings of tcp9 knock-out mutants display a significantly weaker primary root growth inhibition response to cyst nematodes than wild-type Arabidopsis. In older plants, tcp9 reduces the impact of nematode infections on the emergence and growth of secondary roots. Importantly, the altered growth responses by tcp9 are most likely not caused by less biotic stress on the root system, because TCP9 does not affect the number of infections, nematode development, and size of the nematode-induced feeding structures. RNA-sequencing of nematode-infected roots of the tcp9 mutants revealed differential regulation of enzymes involved in reactive oxygen species (ROS) homeostasis and responses to oxidative stress. We also found that root and shoot growth of tcp9 mutants is less sensitive to exogenous hydrogen peroxide and that ROS accumulation in nematode infection sites in these mutants is reduced. Altogether, these observations demonstrate that TCP9 modulates the root system architectural plasticity to nematode infections via ROS-mediated processes. Our study further points at a novel regulatory mechanism contributing to the tolerance of plants to root-feeding nematodes by mitigating the impact of belowground biotic stresses.

Cellular messengers involved in the inhibition of the Arabidopsis primary root growth by bacterial quorum-sensing signal N-decanoyl-L-homoserine lactone

BackgroundN-acyl-homoserine lactones (AHLs) are used as quorum-sensing signals by Gram-negative bacteria, but they can also affect plant growth and disease resistance. N-decanoyl-L-homoserine lactone (C10-HSL) is an AHL that has been shown to inhibit primary root growth in Arabidopsis, but the mechanisms underlying its effects on root architecture are unclear. Here, we investigated the signaling components involved in C10-HSL-mediated inhibition of primary root growth in Arabidopsis, and their interplay, using pharmacological, physiological, and genetic approaches.ResultsTreatment with C10-HSL triggered a transient and immediate increase in the concentrations of cytosolic free Ca2+ and reactive oxygen species (ROS), increased the activity of mitogen-activated protein kinase 6 (MPK6), and induced nitric oxide (NO) production in Arabidopsis roots. Inhibitors of Ca2+ channels significantly alleviated the inhibitory effect of C10-HSL on primary root growth and reduced the amounts of ROS and NO generated in response to C10-HSL. Inhibition or scavenging of ROS and NO neutralized the inhibitory effect of C10-HSL on primary root growth. In terms of primary root growth, the respiratory burst oxidase homolog mutants and a NO synthase mutant were less sensitive to C10-HSL than wild type. Activation of MPKs, especially MPK6, was required for C10-HSL to inhibit primary root growth. The mpk6 mutant showed reduced sensitivity of primary root growth to C10-HSL, suggesting that MPK6 plays a key role in the inhibition of primary root growth by C10-HSL.ConclusionOur results indicate that MPK6 acts downstream of ROS and upstream of NO in the response to C10-HSL. Our data also suggest that Ca2+, ROS, MPK6, and NO are all involved in the response to C10-HSL, and may participate in the cascade leading to C10-HSL-inhibited primary root growth in Arabidopsis.

Arabidopsis sucrose transporter 4 (AtSUC4) is involved in high sucrose-mediated inhibition of root elongation

Sucrose transporters (SUCs/SUTs) play crucial roles in apoplast transport and long-distance distribution of sucrose throughout the whole plant. However, whether and how the Arabidopsis AtSUC4 modulates sucrose import from apoplast to cytosol remains unclear. In the present study, we found that AtSUC4 protein was localized to the plasma membrane in the root. Expression of AtSUC4 in roots was gradually induced with the increasing sucrose concentrations (0%, 2%, 4% and 6%). When feeding high concentrations (4% and 6%) of sucrose, the primary root growth of seedling was inhibited. Interestingly, atsuc4 mutants exhibited longer primary root than the wild type under these conditions, indicating that atsuc4 mutants were less sensitive to excess sucrose. Moreover, the root of atsuc4 mutants accumulated less sucrose and abscisic acid (ABA) and more indole-3-acetic acid (IAA) on 4% and 6% sucrose supplementation. Transcriptomic analysis revealed that numerous genes associated with sugar transport and metabolism, as well as ABA signalling were down-regulated, whereas many IAA signaling-related genes were up-regulated in mutant plants relative to the wild type under 6% sucrose treatment. Collectively, our finding demonstrated that the deficiency of AtSUC4 reduced the inhibition of primary root growth under high sucrose condition, probably through reducing the sucrose transportation and metabolism, and subsequent alteration in IAA and ABA signalling.

Uncoupling Aluminum Toxicity From Aluminum Signals in the STOP1 Pathway.

Aluminum (Al) is a major limiting factor for crop production on acidic soils, inhibiting root growth and plant development. At acidic pH (pH < 5.5), Al3+ ions are the main form of Al present in the media. Al3+ ions have an increased solubility at pH < 5.5 and result in plant toxicity. At higher pH, the free Al3+ fraction decreases in the media, but whether plants can detect Al at these pHs remain unknown. To cope with Al stress, the SENSITIVE TO PROTON RHIZOTOXICITY1 (STOP1) transcription factor induces AL-ACTIVATED MALATE TRANSPORTER1 (ALMT1), a malate-exuding transporter as a strategy to chelate the toxic ions in the rhizosphere. Here, we uncoupled the Al signalling pathway that controls STOP1 from Al toxicity using wild type (WT) and two stop1 mutants carrying the pALMT1:GUS construct with an agar powder naturally containing low amounts of phosphate, iron (Fe), and Al. We combined gene expression [real-time PCR (RT-PCR) and the pALMT1:GUS reporter], confocal microscopy (pSTOP1:GFP-STOP1 reporter), and root growth measurement to assess the effects of Al and Fe on the STOP1-ALMT1 pathway in roots. Our results show that Al triggers STOP1 signaling at a concentration as little as 2 μM and can be detected at a pH above 6.0. We observed that at pH 5.7, 20 μM AlCl3 induces ALMT1 in WT but does not inhibit root growth in stop1 Al-hypersensitive mutants. Increasing AlCl3 concentration (>50 μM) at pH 5.7 results in the inhibition of the stop1 mutants primary root. Using the green fluorescent protein (GFP)-STOP1 and ALMT1 reporters, we show that the Al signal pathway can be uncoupled from the Al toxicity on the root. Furthermore, we observe that Al strengthens the Fe-mediated inhibition of primary root growth in WT, suggesting an interaction between Fe and Al on the STOP1-ALMT1 pathway.

Long-distance blue light signalling regulates phosphate deficiency-induced primary root growth inhibition

Although roots are mainly embedded in the soil, recent studies revealed that light regulates mineral nutrient uptake by roots. However, it remains unclear whether the change in root system architecture in response to different rhizosphere nutrient statuses involves light signaling. Here, we report that blue light regulates primary root growth inhibition under phosphate-deficient conditions through the cryptochromes and their downstream signaling factors. We showed that the inhibition of root elongation by low phosphate requires blue light signal perception at the shoot and transduction to the root. In this process, SPA1 and COP1 play a negative role while HY5 plays a positive role. Further experiments revealed that HY5 is able to migrate from the shoot to root and that the shoot-derived HY5 autoactivates root HY5 and regulates primary root growth by directly activating the expression of LPR1, a suppressor of root growth under phosphate starvation. Taken together, our study reveals a regulatory mechanism by which blue light signaling regulates phosphate deficiency-induced primary root growth inhibition, providing new insights into the crosstalk between light and nutrient signaling.

Dichromate-induced ethylene biosynthesis, perception, and signaling regulate the variance in root growth inhibition among Shaheen basmati and basmati-385 rice varieties.

Heavy metals, including a hexavalent form of chromium (Cr(VI)) increasing accumulation in agricultural soil, cause a significant reduction in quality, yield, and growth of rice varieties worldwide. Screening for the selection of tolerant varieties is essential for conventional and molecular breeding. Shaheen basmati (SB) and basmati-385 (B-385) rice varieties, a subspecies of indica, show different sensitivity to Cr(VI), but the underlying mechanisms of this different sensitivity remain elusive. In the current study, we examine the sensitivity of SB and B-385 based on the root, which is the primary organ that encounters water and soil containing Cr(VI), elongation assay, and ethylene's possible role (a stress-responsive phytohormone) in the process. Our results show that SB's seedlings exhibit hypersensitivity as a higher root elongation inhibition than B-385 under different Cr(VI) concentrations. Hypersensitive SB consistently expresses a higher level of ethylene biosynthesis and signaling-related genes than B-385. Moreover, ethylene signaling antagonist (silver, Ag) and biosynthesis inhibitor (aminoethoxy vinyl glycine, AVG) alleviate the difference in Cr(VI)-induced root growth inhibition between SB and B-385, respectively. Taken together, we conclude that ethylene mediates difference in sensitivity based on the difference in root growth inhibition in different rice varieties. The difference in Cr(VI)-induced root growth inhibition in SB and B-385. (A) Root growth of SB is slightly more as compared to B-385 in control conditions in the Hoagland solutions. (B) Seedlings of SB showed hypersensitivity to 200 μM Cr(VI) compared to B-385 in terms of primary root growth inhibition, which was higher in SB than B-385. Interestingly, Cr(VI)-induced relative transcript level of ethylene biosynthesis, perception, and signaling-related genes was significantly higher in hypersensitive SB than B-385. Current results in association with previous literature show that Cr(VI)-induced ethylene biosynthesis is regulating Cr(VI)-induced ethylene perception, signaling, and associated Cr(VI)-induced ethylene-mediated primary root growth inhibition. Conclusively, the difference in ethylene quantities in both varieties mediates the difference in root growth inhibition between SB and B-385 (C and E). The difference in Cr(VI)-induce root growth inhibition between SB and B-385 was significantly alleviated by ethylene signaling inhibitor (10 μM Ag, as AgNO3) and ethylene biosynthesis inhibitor (10 μM AVG) treatment in the presence of 200 μM Cr(VI), respectively. (D) Ethylene biosynthesis precursor (10 μM ACC) treatment-mediated induced root growth inhibition difference between SB and B-385 was not significant, which may be because of enough quantity of the Cr(VI)-mediated ethylene accumulation or unknown limiting factor. Arrows mean addition and an increase in expression, and T-line means suppression or inhibition. The width of the pointers (arrows) is proportional to the gene expression level.

JASMONATE RESISTANT 1 negatively regulates root growth under boron deficiency in Arabidopsis.

Boron (B) is an essential micronutrient for plant growth and development. Jasmonic acid (JA) plays pivotal roles in plant growth, but the underlying molecular mechanism of JA involvement in B-deficiency-induced root growth inhibition is yet to be explored. In this study, we investigated the response of JA to B deficiency and the mechanism of JAR1-dependent JA signaling in root growth inhibition under B deficiency in Arabidopsis. B deficiency enhanced JA signaling in roots, and root growth inhibition was partially restored by JA biosynthesis inhibition. The jar1-1 (jasmonate-resistant 1, JAR1) mutant, and mutants of coronatine-insensitive 1 (coi1-2) and myc2 defective in JA signaling showed insensitivity to B deficiency. The ethylene-overproduction mutant eto1 and ethylene-insensitive mutant etr1 showed sensitivity and insensitivity to B deficiency, respectively, suggesting that ethylene is involved in the inhibition of primary root growth under B deficiency. Furthermore, after a decline in levels of EIN3, which may contribute to root growth, ethylene signaling was weakened in the jar1-1 mutant root under B deficiency. Under B deficiency, B concentrations were increased in the roots and shoots of the jar1-1 mutant, owing to the large root system and its activity. Therefore, our findings revealed that JA, which is involved in the inhibition of root growth under B deficiency, is regulated by JAR1-activated JA and ethylene signaling pathways.

Cadmium, nickel, copper, and zinc influence on microfilament organization in Arabidopsis root cells.

The plant cytoskeleton orchestrates such fundamental processes in cells as division, growth and development, polymer cross-linking, membrane anchorage, etc. Here, we describe the influence of Cd2+ , Ni2+ , Zn2+ , and Cu2+ on root development and vital organization of actin filaments into different cells of Arabidopsis thaliana line expressing GFP-FABD2. CdSO4 , NiSO4 , CuSO4 , and ZnSO4 were used in concentrations of 5-20 µM in this study. It was found that Cd, Ni, and Cu cause dose-dependent primary root growth inhibition and alteration of the root morphology, whereas Zn slightly stimulates root growth and does not affect the morphology of Arabidopsis roots. This growth inhibition/stimulation correlated with the various sensitivities of microfilaments to Cd, Ni, Cu, and Zn action. It was established that Cd, Ni, and Cu affected predominantly the actin filaments of meristematic cells. Cells of transition and elongation zones demonstrated strong actin filament sensitivity to Cd and Cu. Microfilaments of elongating root cells were more sensitive to Ni and Cu. Although Cd, Ni, and Cu stimulated root hair growth after long-term treatment, actin filaments were destroyed after 1 h exposure with these metals. Zn did not disrupt native actin filamentorganization in root cells. Thus, our investigation shows that microfilaments act as sensitive cellular targets for Cd, Ni, and Cu. More data on effects on native actin filaments organization would contribute to a better understanding of plant tolerance mechanisms to the action of these metals.

Variable Light Condition Improves Root Distribution Shallowness and P Uptake of Soybean in Maize/Soybean Relay Strip Intercropping System

In this study, soybean root distribution in an inter-cropping system was influenced by various environmental and biotic cues. However, it is still unknown how root development and distribution in inter-cropping responds to aboveground light conditions. Herein, soybeans were inter- and monocropped with P (phosphorus) treatments of 0 and 20 kg P ha yr−1 (P0 and P20, respectively) in field experiment over 4 years. In 2019, a pot experiment was conducted as the supplement to the field experiment. Shade from sowing to V5 (Five trifoliolates unroll) and light (SL) was used to imitate the light condition of soybeans in a relay trip inter-cropping system, while light then shade from V5 to maturity (LS) was used to imitate the light condition of soybeans when monocropped. Compared to monocropping, P uptake and root distribution in the upper 0–15 cm soil layer increased when inter-cropped. Inter-cropped soybeans suffered serious shade by maize during a common-growth period, which resulted in the inhibition of primary root growth and a modified auxin synthesis center and response. During the solo-existing period, plant photosynthetic capacity and sucrose accumulation increased under ameliorated light in SL (shade-light). Increased light during the reproductive stage significantly decreased leaf P concentration in SL under both P-sufficient and P-deficient conditions. Transcripts of a P starvation response gene (GmPHR25) in leaves and genes (GmEXPB2) involved in root growth were upregulated by ameliorated light during the reproductive stage. Furthermore, during the reproductive stage, more light interception increased the auxin concentration and expression of GmYUCCA14 (encoding the auxin synthesis) and GmTIR1C (auxin receptor) in roots. Across the field and pot experiments, increased lateral root growth and shallower root distribution were associated with inhibited primary root growth during the seedling stage and ameliorated light conditions in the reproductive stage. Consequently, this improved topsoil foraging and P uptake of inter-cropped soybeans. It is suggested that the various light conditions (shade-light) mediating leaf P status and sucrose transport can regulate auxin synthesis and respond to root formation and distribution.