Root Signal Research Articles

Transcriptome skimming of lentil (Lens culinaris Medikus) cultivars with contrast reaction to salt stress.

Extensive transcriptomic skimming was conducted to decipher molecular, morphological, physiological, and biochemical responses in salt-tolerant (PDL-1) and salt-sensitive (L-4076) cultivars under control (0mM NaCl) and salinity stress (120mM NaCl) conditions at seedling stage. Morphological, physiological, and biochemical studies revealed that PDL-1 exhibited no salt injury and had higher K+/Na+ ratio, relative water content (RWC), chlorophyll, glycine betaine, and soluble sugars in leaves while lower H2O2 induced fluorescence signals in roots as compared to L-4076. Transcriptomic profile revealed a total of 17,433 significant differentially expressed genes (DEGs) under different treatments and cultivar combinations that include 2557 upregulated and 1533 downregulated transcripts between contrasting cultivars under salt stress. Accuracy of transcriptomic analysis was validated through quantification of 10 DEGs via quantitative real-time polymerase chain reaction (qRT-PCR). DEGs were functionally characterized by Gene Ontology (GO) analysis and assigned to various metabolic pathways using MapMan. DEGs were found to be significantly associated with phytohormone-mediated signal transduction, cellular redox homoeostasis, secondary metabolism, nitrogen metabolism, and cellular stress signaling. The present study revealed putative molecular mechanism of salinity tolerance in lentil together with identification of 5643 simple sequence repeats (SSRs) and 176,433 single nucleotide polymorphisms (SNPs) which can be utilized to enhance linkage maps density along with detection of quantitative trait loci (QTLs) associated with traits of interests. Stress-related pathways identified in this study divulged plant functioning that can be targeted to improve salinity stress tolerance in crop species.

НАКОПЛЕНИЕ, РАСПРЕДЕЛЕНИЕ И ФУНКЦИОНАЛЬНАЯ РОЛЬ АБК ПРИ КРАТКОВРЕМЕННОМ ДЕЙСТВИИ ЗАСОЛЕНИЯ НА РАСТЕНИЯ ПШЕНИЦЫ

Local effects on plant roots or shoots are accompanied by a change of plant hormones concentration providing signal transduction in plants and their adaptation to changing environmental conditions. It is known that plants respond to drought stress by increasing the concentration of abscisic acid (ABA) in xylem sap which leads to decrease in stomatal conductance to prevent plant water loss from transpirational pathways. Earlier, we found a rapid leaf ABA accumulation in barley and wheat plants under influence of the shortterm salinity. However, the mechanism of the salt stress induced rapid accumulation of abscisic acid in plant leaves remained unclear. The aim of this study was to investigate whether the salt-induced rapid accumulation of abscisic acid in the leaves was the result of its inflow from the roots (as a root signal). In our experiments the short-term salinity did not increase but decreased the concentration of abscisic acid in xylem sap of wheat plants. Thus, detected accumulation of ABA in the leaves did not result from an increase in its inflow from the roots. Apparently leaf ABA accumulation already detected in 15 min after the onset of salinity stress could be a local reaction due to its metabolism in the shoot itself. The decrease in the leaf water potential could induce the change of abscisic acid metabolism pathways in the shoot that led to the accumulation of this hormone. A small short-term accumulation of ABA in the roots did not lead to an increase in their hydraulic conductivity.

Actin filaments mediated root growth inhibition by changing their distribution under UV-B and hydrogen peroxide exposure in Arabidopsis

BackgroundUV-B signaling in plants is mediated by UVR8, which interacts with transcriptional factors to induce root morphogenesis. However, research on the downstream molecules of UVR8 signaling in roots is still scarce. As a wide range of functional cytoskeletons, how actin filaments respond to UV-B-induced root morphogenesis has not been reported. The aim of this study was to investigate the effect of actin filaments on root morphogenesis under UV-B and hydrogen peroxide exposure in Arabidopsis.ResultsA Lifeact-Venus fusion protein was used to stain actin filaments in Arabidopsis. The results showed that UV-B inhibited hypocotyl and root elongation and caused an increase in H2O2 content only in the root but not in the hypocotyl. Additionally, the actin filaments in hypocotyls diffused under UV-B exposure but were gathered in a bundle under the control conditions in either Lifeact-Venus or uvr8 plants. Exogenous H2O2 inhibited root elongation in a dose-dependent manner. The actin filaments changed their distribution from filamentous to punctate in the root tips and mature regions at a lower concentration of H2O2 but aggregated into thick bundles with an abnormal orientation at H2O2 concentrations up to 2 mM. In the root elongation zone, the actin filament arrangement changed from lateral to longitudinal after exposure to H2O2. Actin filaments in the root tip and elongation zone were depolymerized into puncta under UV-B exposure, which showed the same tendency as the low-concentration treatments. The actin filaments were hardly filamentous in the maturation zone. The dynamics of actin filaments in the uvr8 group under UV-B exposure were close to those of the control group.ConclusionsThe results indicate that UV-B inhibited Arabidopsis hypocotyl elongation by reorganizing actin filaments from bundles to a loose arrangement, which was not related to H2O2. UV-B disrupted the dynamics of actin filaments by changing the H2O2 level in Arabidopsis roots. All these results provide an experimental basis for investigating the interaction of UV-B signaling with the cytoskeleton.

Studying Gene Expression in Irradiated Barley Cultivars: PM19L-like and CML31-like Expression as Possible Determinants of Radiation Hormesis Effect

Gamma (γ)-irradiation of plants at low doses can provoke a broad range of growth-stimulating effects. In order to reveal universal target genes that are involved in molecular pathways of radiation hormesis establishment, we studied nine barley cultivars for their tolerance to γ-irradiation of seeds. Four morphological traits were assessed in barley seedlings after γ-irradiation of seeds at 20 Gy. Nine cultivars were sorted according to the sensitivity to irradiation as γ-stimulated, “no morphological effect”, or γ-inhibited. Gene expression of 17 candidate genes was evaluated for the 7 most contrasting cultivars. Changes in expression of barley homologues of PM19L and CML31 were suggested as possible determinants of radiation hormesis effect. The possible role of jasmonate signaling in roots in radiation growth stimulations was revealed. Morphological analysis and gene expression study showed that the genetic background of a cultivar plays an important role in eustress responses to low-dose γ-irradiation of seeds.

Differentiate responses of tetraploid and hexaploid wheat (Triticum aestivum L.) to moderate and severe drought stress: a cue of wheat domestication

ABSTRACT Differentiate mechanism of wheat species in response to contrasting drought stress gradients implies a cue of its long-term domestication. In the present study, three water regimes including well-watered control (WW, 80% field water capacity (FC)), moderate drought stress (MS, 50% FC,) and severe drought stress (SS, 30% FC) were designed to reveal different responses of eight wheat species (four tetraploid and four hexaploid) representing different breeding decades and genetic origins to drought stresses. The data indicated that 50% FC and 30% FC fell into the soil moisture threshold range of non-hydraulic and hydraulic root signal occurrence, respectively. In general, grain yield, grain number/spike weight per plant, aboveground biomass, harvest index (HI) and water use efficiency (WUE) were significantly higher in hexaploid species than those of tetraploid species under drought stress (P < .05). Particularly, non-hydraulic root signal was triggered and continuously operated under 50% FC, while hydraulic root signal was observed under 30% FC, respectively. Under 80% FC, the allometric exponent (ɑ) of Maboveground vs Mroot decreased from tetraploid to hexaploid (both were of <1), indicating that during the domestication, the hexaploid species allocated less biomass to root system. For the relationship of Mear vs Mvegetative, the ɑ value was significantly greater in the hexaploid species, showing that hexaploid wheat distributed more biomass to ear than tetraploid to improve yield. Under 50% FC, this trend was enhanced. However, under 30% FC, there was no significant difference in the ɑ value between two species. Additionally, correlation analyses on yield formation affirmed the above results. Therefore, drought tolerance tended to be enhanced in hexaploid species under the pressure of artificial selection than that of tetraploid species. When drought stress exceeded a certain threshold, both species would be negatively seriously affected and followed a similar mechanism for better survival.

A fluorescence-based high-throughput screening method for cytokinin translocation mutants

BackgroundCytokinins are one kind of phytohormones essential for plant growth, development and stress responses. In the past half century, significant progresses have been made in the studies of cytokinin signal transduction and metobolic pathways, but the mechanism of cytokinin translocation is poorly understood. Arabidopsis (Arabidopsis thaliana) response regulator 5 (ARR5) is a type-A response factor in cytokinin signaling which is induced by cytokinins and has been used as a reporter gene for the endogenous cytokinins in Arabidopsis. Here, we report a fluorescence-based high-throughput method to screen cytokinin translocation mutants using an ethyl methyl sulfone (EMS) mutagenesis library generated with ARR5::eGFP transgenic plants.ResultsThe seedlings with enhanced green fluorescent protein (GFP) signal in roots were screened in a luminescence imaging system (LIS) in large scale to obtain mutants with over-accumulated cytokinins in roots. The selected mutants were confirmed under a fluorescence microscopy and then performed phenotypic analysis. In this way, we obtained twelve mutants with elevated GFP signal in the roots and further found three of them displayed reduced GFP signal in the aerial tissues. Two of the mutants were characterized and proved to be the atabcg14 allelic mutants which are defective in the long-distance translocation of root-synthesized cytokinins.ConclusionsWe provide a strategy for screening mutants defective in cytokinin translocation, distribution or signaling. The strategy can be adapted to establish a system for screening mutants defective in other hormone transporters or signaling components using a fluorescence reporter.

Root exudate signals in plant-plant interactions.

Plant-to-plant signalling is a key mediator of interactions among plant species. Plants can perceive and respond to chemical cues emitted from their neighbours, altering survival and performance, impacting plant coexistence and community assembly. An increasing number of studies indicate root exudates as key players in plant-to-plant signalling. Root exudates mediate root detection and behaviour, kin recognition, flowering and production, driving inter- and intra-specific facilitation in cropping systems and mixed-species plantations. Altered interactions may be attributed to the signalling components within root exudates. Root ethylene, strigolactones, jasmonic acid, (-)-loliolide and allantoin are signalling chemicals that convey information on local conditions in plant-plant interactions. These root-secreted signalling chemicals appear ubiquitous in plants and trigger a series of belowground responses inter- and intra-specifically, involving molecular events in biosynthesis, secretion and action. The secretion of root signals, mainly mediated by ATP-binding cassette transporters, is critical. Root-secreted signalling chemicals and their molecular mechanisms are rapidly revealing a multitude of fascinating plant-plant interactions. However, many root signals, particularly species-specific signals and their underlying mechanisms, remain to be uncovered due to methodological limitations and root-soil interactions. A thorough understanding of root-secreted chemical signals and their mechanisms will offer many ecological implications and potential applications for sustainable agriculture.

Differentiate effects of non-hydraulic and hydraulic root signaling on yield and water use efficiency in diploid and tetraploid wheat under drought stress

Non-hydraulic root signals (nHRS) and hydraulic root signals (HRS) are important mechanisms that play a major role in determining plant productivity under drought stress. In the present study, six wheat varieties (three diploid and three tetraploid) were used to investigate the variation of yield, its components, water use efficiency (WUE) and biomass allocation under two signals. At the jointing stage, three water treatments were set up: i) well-watered control (WW, 80 % field water capacity (FC)), ii) moderate water stress (MS, 50 % FC) and iii) severe water stress (SS, 30 % FC). The results showed that around 50 % FC, wheat activated the nHRS to respond to drought. While around 30 % FC, wheat activated the HRS as a response to deeper drought. Under the operation of nHRS, the reduction of yield, aboveground biomass and WUE of diploid species was greater than that of tetraploid ones, but there were no differences under the operation of HRS. It could be argued that two different wheat species followed differentiate positive defense strategy in response to nHRS, but fell into a similar negative adaptive strategy under the HRS. The ploidy level of wheat also had a significant effect on wheat yield composition, WUE and biomass allocation model. As such, grain yield, grain number and spike weight per plant, aboveground biomass, harvest index (HI) and WUE were significantly greater in the tetraploid species than the diploids ones. In addition, the retention rate of aboveground biomass and grain decreased under the operation of nHRS and HRS. Path analysis showed that spikelet number, thousand grain weight and grain number were the main factors affecting yield formation. Grain number had the greatest direct effect on yield, while spikelet number and its grain number exerted the main effect on yield. These results were consistent under both signals.

ZnO nanoparticles induce cell wall remodeling and modify ROS/ RNS signalling in roots of Brassica seedlings

Cell wall-associated defence against zinc oxide nanoparticles (ZnO NPs) as well as nitro-oxidative signalling and its consequences in plants are poorly examined. Therefore, this study compares the effect of chemically synthetized ZnO NPs (~45 nm, 25 or 100 mg/L) on Brassica napus and Brassica juncea seedlings. The effects on root biomass and viability suggest that B. napus is more tolerant to ZnO NP exposure relative to B. juncea. This may be due to the lack of Zn ion accumulation in the roots, which is related to the increase in the amount of lignin, suberin, pectin and in peroxidase activity in the roots of B. napus. TEM results indicate that root cell walls of 25 mg/L ZnO NP-treated B. napus may bind Zn ions. Additionally, callose accumulation possibly contribute to root shortening in both Brassica species as the effect of 100 mg/L ZnO NPs. Further results suggest that in the roots of the relatively sensitive B. juncea the levels of superoxide radical, hydrogen peroxide, hydrogen sulfide, nitric oxide, peroxinitrite and S-nitrosoglutathione increased as the effect of high ZnO NP concentration meaning that ZnO NP intensifies nitro-oxidative signalling. In B. napus; however, reactive oxygen species signalling was intensified, but reactive nitrogen species signalling wasn't activated by ZnO NPs. Collectively, these results indicate that ZnO NPs induce cell wall remodeling which may be associated with ZnO NP tolerance. Furthermore, plant tolerance against ZnO NPs is associated rather with nitrosative signalling than oxidative modifications.

Cold Plasma Treatment of Sunflower Seeds Modulates Plant-Associated Microbiome and Stimulates Root and Lateral Organ Growth.

Cold atmospheric pressure (CP) plasma irradiation of seeds has been shown to promote plant growth, but the molecular basis of this phenomenon is poorly understood. In our study, optimum irradiation of common sunflower seeds using a dielectric barrier discharge CP device stimulated growth of sunflower lateral organs and roots by 9–14% compared to the control. Metagenomic analysis revealed that the structure of plant-associated bacterial assembly was greatly modified upon CP treatment and could be attributed to the antimicrobial effect of CP-generated reactive species. The treatment resulted in the domination of spore forming Mycobacterium sp. in the above-ground tissues of the seedlings. While the overall bacterial diversity in the roots was barely affected, the CP-induced shift in microbial composition is the likely basis for the observed seedling root growth stimulation and the long-term effect on lateral organ growth and could be mediated by increase in water uptake and/or direct root signaling. Low amplitude protein abundance differences were detected in the roots of the emerging seedlings that are characteristic to low intensity stress stimuli response and could be linked to the changes in plant-associated microbiome upon CP treatment.

Root-to-shoot signalling in mycorrhizal tomato plants upon Botrytis cinerea infection

Arbuscular mycorrhizal symbiosis is restricted in roots, but it also improves shoot responses against leaf challenges, a phenomenon known as Mycorrhiza-Induced Resistance (MIR). This study focuses on mycorrhizal root signals that may orchestrate shoot defence responses. Metabolomic analysis of non-mycorrhizal and mycorrhizal plants upon Botrytis cinerea infection showed that roots rearrange their metabolome mostly in response to the symbiosis, whereas in shoots a stronger impact of the infection is observed. Specific clusters of compounds in shoots and roots display a priming profile suggesting an implication in the enhanced resistance observed in mycorrhizal plants. Among the primed pathways in roots, lignans showed the highest number of hits followed by oxocarboxylic acids, compounds of the amino acid metabolism, and phytohormones. The lignan yatein was present at higher concentrations in roots, root efflux and leaves of mycorrhizal plants This lignan displayed in vitro antimicrobial activity against B. cinerea and it was also functional protecting tomato plants. Besides, several JA defence-related genes were upregulated in mycorrhizal roots regardless of the pathogen infection, whereas PIN-II was primed in roots of mycorrhizal infected plants. These observations suggest that the enhanced resistance in shoots during MIR may be coordinated by lignans and oxylipins with the participation of roots.

Strigolactones Interact With Nitric Oxide in Regulating Root System Architecture of Arabidopsis thaliana.

Both nitric oxide (NO) and strigolactone (SL) are growth regulating signal components in plants; however, regarding their possible interplay our knowledge is limited. Therefore, this study aims to provide new evidence for the signal interplay between NO and SL in the formation of root system architecture using complementary pharmacological and molecular biological approaches in the model Arabidopsis thaliana grown under stress-free conditions. Deficiency of SL synthesis or signaling (max1-1 and max2-1) resulted in elevated NO and S-nitrosothiol (SNO) levels due to decreased S-nitrosoglutathione (GSNO) reductase (GSNOR) protein abundance and activity indicating that there is a signal interaction between SLs and GSNOR-regulated levels of NO/SNO. This was further supported by the down-regulation of SL biosynthetic genes (CCD7, CCD8 and MAX1) in GSNOR-deficient gsnor1-3. Based on the more pronounced sensitivity of gsnor1-3 to exogenous SL (rac-GR24, 2 µM), we suspected that functional GSNOR is needed to control NO/SNO levels during SL-induced primary root (PR) elongation. Additionally, SLs may be involved in GSNO-regulated PR shortening as suggested by the relative insensitivity of max1-1 and max2-1 mutants to exogenous GSNO (250 µM). Collectively, our results indicate a connection between SL and GSNOR-regulated NO/SNO signals in roots of A. thaliana grown in stress-free environment. As this work used max2-1 mutant and rac-GR24 exerting unspecific effects to both SL and karrikin signaling, it cannot be ruled out that karrikins are partly responsible for the observed effects, and this issue needs further clarification in the future.

Root Involvement in Plant Responses to Adverse Environmental Conditions

Climate change is altering the environment in which plants grow and survive. An increase in worldwide Earth surface temperatures has been already observed, together with an increase in the intensity of other abiotic stress conditions such as water deficit, high salinity, heavy metal intoxication, etc., generating harmful conditions that destabilize agricultural systems. Stress conditions deeply affect physiological, metabolic and morphological traits of plant roots, essential organs for plant survival as they provide physical anchorage to the soil, water and nutrient uptake, mechanisms for stress avoidance, specific signals to the aerial part and to the biome in the soil, etc. However, most of the work performed until now has been mainly focused on aerial organs and tissues. In this review, we summarize the current knowledge about the effects of different abiotic stress conditions on root molecular and physiological responses. First, we revise the methods used to study these responses (omics and phenotyping techniques). Then, we will outline how environmental stress conditions trigger various signals in roots for allowing plant cells to sense and activate the adaptative responses. Later, we discuss on some of the main regulatory mechanisms controlling root adaptation to stress conditions, the interplay between hormonal regulatory pathways and the global changes on gene expression and protein homeostasis. We will present recent advances on how the root system integrates all these signals to generate different physiological responses, including changes in morphology, long distance signaling and root exudation. Finally, we will discuss the new prospects and challenges in this field.

Arabidopsis Lectin EULS3 Is Involved in ABA Signaling in Roots.

The Arabidopsis thaliana lectin ArathEULS3 is upregulated in particular stress conditions and upon abscisic acid (ABA) treatment. ABA is a plant hormone important for plant growth and stress responses. During stress ABA is perceived by PYR/PYL/RCAR receptors, inhibiting protein phosphatases PP2Cs thereby enabling SNRK2s kinases to start downstream phosphorylation cascades and signaling. PYL9, one of the ABA receptors was identified as an interacting partner for ArathEULS3. Promoter::GUS activity studies revealed the expression of ArathEULS3 in the central root cylinder and the cells flanking young lateral root primordia, and showed enhanced expression in root tips after ABA treatment. Transcript levels for ArathEULS3 increased after exposure to ABA and osmotic treatments. ArathEULS3 CRISPR KO mutants served as a tool to expand the knowledge on the role of ArathEULS3 in plant development. KO lines revealed a longer root system compared to WT plants, and showed reduced sensitivity to ABA, salt, and osmotic conditions. Additionally it was noted that the KO mutants had more emerged lateral roots when grown in high osmotic conditions. Together these data suggest that ArathEULS3 may be an important player in ABA responses in roots.

Exogenous strigolactones impact metabolic profiles and phosphate starvation signalling in roots.

Strigolactones (SLs) are important ex-planta signalling molecules in the rhizosphere, promoting the association with beneficial microorganisms, but also affecting plant interactions with harmful organisms. They are also plant hormones in-planta, acting as modulators of plant responses under nutrient-deficient conditions, mainly phosphate (Pi) starvation. In the present work, we investigate the potential role of SLs as regulators of early Pi starvation signalling in plants. A short-term pulse of the synthetic SL analogue 2'-epi-GR24 promoted SL accumulation and the expression of Pi starvation markers in tomato and wheat under Pi deprivation. 2'-epi-GR24 application also increased SL production and the expression of Pi starvation markers under normal Pi conditions, being its effect dependent on the endogenous SL levels. Remarkably, 2'-epi-GR24 also impacted the root metabolic profile under these conditions, promoting the levels of metabolites associated to plant responses to Pi limitation, thus partially mimicking the pattern observed under Pi deprivation. The results suggest an endogenous role for SLs as Pi starvation signals. In agreement with this idea, SL-deficient plants were less sensitive to this stress. Based on the results, we propose that SLs may act as early modulators of plant responses to P starvation.

Local and Systemic Effects of Brassinosteroid Perception in Developing Phloem.

The plant vasculature is an essential adaptation to terrestrial growth. Its phloem component permits efficient transfer of photosynthates between source and sink organs but also transports signals that systemically coordinate physiology and development. Here, we provide evidence that developing phloem orchestrates cellular behavior of adjacent tissues in the growth apices of plants, the meristems. Arabidopsis thaliana plants that lack the three receptor kinases BRASSINOSTEROID INSENSITIVE 1 (BRI1), BRI1-LIKE 1 (BRL1), and BRL3 ("bri3" mutants) can no longer sense brassinosteroid phytohormones and display severe dwarfism as well as patterning and differentiation defects, including disturbed phloem development. We found that, despite the ubiquitous expression of brassinosteroid receptors in growing plant tissues, exclusive expression of the BRI1 receptor in developing phloem is sufficient to systemically correct cellular growth and patterning defects that underlie the bri3 phenotype. Although this effect is brassinosteroid-dependent, it cannot be reproduced with dominant versions of known downstream effectors of BRI1 signaling and therefore possibly involves a non-canonical signaling output. Interestingly, the rescue of bri3 by phloem-specific BRI1 expression is associated with antagonism toward phloem-specific CLAVATA3/EMBRYO SURROUNDING REGION-RELATED 45 (CLE45) peptide signaling in roots. Hyperactive CLE45 signaling causes phloem sieve element differentiation defects, and consistently, knockout of CLE45 perception in bri3 background restores proper phloem development. However, bri3 dwarfism is retained in such lines. Our results thus reveal local and systemic effects of brassinosteroid perception in the phloem: whereas it locally antagonizes CLE45 signaling to permit phloem differentiation, it systemically instructs plant organ formation via a phloem-derived, non-cell-autonomous signal.

The GDSL Lipase MHZ11 Modulates Ethylene Signaling in Rice Roots.

Ethylene plays important roles in plant growth and development, but the regulation of ethylene signaling is largely unclear, especially in crops such as rice (Oryza sativa). Here, by analysis of the ethylene-insensitive mutant mao huzi 11 (mhz11), we identified the GDSL lipase MHZ11, which modulates ethylene signaling in rice roots. MHZ11 localized to the endoplasmic reticulum membrane and has acyl-hydrolyzing activity. This activity affects the homeostasis of sterols in rice roots and is required for root ethylene response. MHZ11 overexpression caused constitutive ethylene response in roots. Genetically, MHZ11 acts with the ethylene receptor ETHYLENE RESPONSE SENSOR2 (OsERS2) upstream of CONSTITUTIVE TRIPLE RESPONSE2 (OsCTR2) and ETHYLENE INSENSITIVE2 (OsEIN2). The mhz11 mutant maintains more OsCTR2 in the phosphorylated form whereas MHZ11 overexpression promotes ethylene-mediated inhibition of OsCTR2 phosphorylation. MHZ11 colocalized with the ethylene receptor OsERS2, and its effect on OsCTR2 phosphorylation requires ethylene perception and initiation of ethylene signaling. The mhz11 mutant overaccumulated sterols and blocking sterol biosynthesis partially rescued the mhz11 ethylene response, likely by reducing receptor-OsCTR2 interaction and OsCTR2 phosphorylation. We propose that MHZ11 reduces sterol levels to impair receptor-OsCTR2 interactions and OsCTR2 phosphorylation for triggering ethylene signaling. Our study reveals a mechanism by which MHZ11 participates in ethylene signaling for regulation of root growth in rice.

Increased Flavonol Levels in Tobacco Expressing AcFLS Affect Flower Color and Root Growth

The onion (Allium cepa L.) flavonol synthase (AcFLS-HRB) gene, encoding an enzyme responsible for flavonol biosynthesis in yellow onion, was recently identified and enzymatically characterized. Here, we performed an in vivo feeding assay involving bacterial expression of AcFLS-HRB and observed that it exhibited both flavanone 3-hydroxylase (F3H) and FLS activity. Transgenic tobacco (Nicotiana tabacum) expressing AcFLS-HRB produced lighter-pink flowers compared to wild-type plants. In transgenic petals, AcFLS-HRB was highly expressed at the mRNA and protein levels, and most AcFLS-HRB protein accumulated in the insoluble microsomal fractions. High-performance liquid chromatography (HPLC) analysis showed that flavonol levels increased but anthocyanin levels decreased in transgenic petals, indicating that AcFLS-HRB is a functional gene in planta. Gene expression analysis showed the reduced transcript levels of general phenylpropanoid biosynthetic genes and flavonoid biosynthetic genes in AcFLS-HRB overexpressed tobacco petals. Additionally, transgenic tobacco plants at the seedling stages showed increased primary root and root hair length and enhanced quercetin signals in roots. Exogenous supplementation with quercetin 3-O-rutinoside (rutin) led to the same phenotypic changes in root growth, suggesting that rutin is the causal compound that promotes root growth in tobacco. Therefore, augmenting flavonol levels affects both flower color and root growth in tobacco.

Expression of the Legume-Specific Nod Factor Receptor Proteins Alters Developmental and Immune Responses in Rice

Legumes form symbiosis with rhizobia, which fix nitrogen for the benefit of host plant in return for carbon resources. Development of this unique symbiosis in legumes is triggered by rhizobia-secreted nodulation (Nod) factors (NFs). NFs, upon perception, activate Nod signaling cascade, leading to reprogramming of host cell (root) developmental networks to pave way for accommodating rhizobial symbionts. A long-cherished goal of legume-rhizobia symbiosis research is to extend this symbiotic nitrogen-fixing capacity to cereal plants such as rice. As a part of achieving this ultimate goal, in this work, initially we expressed legume-specific Nod factor receptor protein (NFRP) genes, MtNFP, MtLYK3, and LjLNP, in rice and assessed their impact on NF perception and consequently triggered biological responses in roots. RNA-seq analysis revealed that roots of both control and NFRP-expressing plants perceive NFs, but NFs elicited contrasting impacts on gene expression patterns in roots of these plants. In contrast to suppressive role of NFs on expression of several genes involved in innate immune response in roots of control plants, in NFRP-expressing plants, NFs triggered massive upregulation of a vast array of genes associated with signaling, defense response, and secondary metabolism networks in roots. Expression of NFRPs in rice also conferred root hairs the ability to respond to NFs in terms of exhibiting deformations, albeit at low levels. Together, results of the study demonstrated that rice plants have inherent ability to perceive NFs, but the expression of legume NFRPs rendered rice roots hypersensitive to NFs.

Foliar herbivory by caterpillars and aphids differentially affects phytohormonal signalling in roots and plant defence to a root herbivore.

Plant‐mediated interactions are an important force in insect ecology. Through such interactions, herbivores feeding on leaves can affect root feeders. However, the mechanisms regulating the effects of above‐ground herbivory on below‐ground herbivores are poorly understood. Here, we investigated the performance of cabbage root fly larvae (Delia radicum) on cabbage plants (Brassica oleracea) previously exposed to above ground herbivores belonging to two feeding guilds: leaf chewing diamondback moth caterpillars (Plutella xylostella) or phloem‐feeding cabbage aphids (Brevicoryne brassicae). Our study focusses on root‐herbivore performance and defence signalling in primary roots by quantifying phytohormones and gene expression. We show that leaf herbivory by caterpillars, but not by aphids, strongly attenuates root herbivore performance. Above‐ground herbivory causes changes in primary roots in terms of gene transcripts and metabolites involved in plant defence. Feeding by below‐ground herbivores strongly induces the jasmonate pathway in primary roots. Caterpillars feeding on leaves cause a slight induction of the primary root jasmonate pathway and interact with plant defence signalling in response to root herbivores. In conclusion, feeding by a leaf chewer and a phloem feeder differentially affects root‐herbivore performance, root‐herbivore‐induced phytohormonal signalling, and secondary metabolites.