Root Epidermis Research Articles

Negative feedback regulation of GLABRA1 contributes to epidermal cell patterning in the Arabidopsis root

GLABRA1 (GL1), which encodes an R2R3 MYB transcription factor, is a key regulator of trichome patterning in the aerial organs of Arabidopsis thaliana. Although it has been generally assumed that GL1 functions exclusively in shoots and is not expressed in roots, reverse transcription polymerase chain reaction (RT-PCR) analysis has revealed that GL1 is indeed expressed in roots. To investigate whether GL1 plays a role in root epidermal patterning, we analyzed the effects of gl1 mutations in sensitized genetic backgrounds. Our findings show that gl1 mutants enhance the root epidermal phenotype of a weak allele of the werewolf (wer) mutant and suppress the phenotype of the caprice (cpc) mutant. We also demonstrate that the GL1 promoter is active in N-position epidermal cells, and that the GFP-GL1 fusion protein is predominantly localized in the nucleus of N-position cells. Furthermore, we provide evidence that GL1 expression is positively regulated by WER, GLABRA3, ENHANCER OF GLABRA3, and TRANSPARENT TESTA GLABRA1, while negatively regulated by CPC, TRIPTYCHON, and GLABRA2 (GL2). Notably, GL2, which is positively regulated by GL1, moderately represses GL1 expression, and both GL1 and GL2 are positively regulated by WER in N-position cells. These findings suggest that a negative feedback regulation of GL1 expression via GL2 contributes to the fine-tuning of non-hair cell fate determination in Arabidopsis root epidermis.

An inquiry into the radial patterning of root hair cell distribution in eudicots.

The root epidermis of tracheophytes consists of hair-forming cells (HCs) and nonhair cells (NCs). The HC distribution pattern is classified into three types: random (Type I), vertically alternating (Type II), and radial (Type III). Type III is found only in core eudicots and is known to be position-dependent in superrosids with HCs positioned between two underlying cortical cells. However, the evolution of Type III and the universality of its position dependency in eudicots remain unclear. We surveyed the HC distribution in basal and Type III-exhibiting core eudicots and conducted genomic analyses to get insight into whether eudicots share the same genetic network to establish Type III. Our survey revealed no canonical Type III in basal eudicots but a reverse Type III, with NCs between two cortical cells and HCs on a single cortical cell, in Papaveraceae of basal eudicots. Type III-exhibiting species from both superrosids and superasterids showed the canonical position dependency of HCs. However, some key components for Type III determination were absent in the genomes of Papaveraceae and Type III-exhibiting superasterids. Our findings identify a novel position-dependent type of HC patterning, reverse Type III, and suggest that Type III emerged independently or diversified during eudicot evolution.

Polarly localized Bro1 domain proteins regulate PIN-FORMED abundance and root gravitropic growth in Arabidopsis

The developmental plasticity of the root system plays an essential role in the adaptation of plants to the environment. Among many other signals, auxin and its directional, intercellular transport are critical in regulating root growth and development. In particular, the PIN-FORMED2 (PIN2) auxin exporter acts as a key regulator of root gravitropic growth. Multiple regulators have been reported to be involved in PIN2-mediated root growth; however, our information remains incomplete. Here, we identified ROWY Bro1-domain proteins as important regulators of PIN2 sorting control. Genetic analysis revealed that Arabidopsis rowy1 single mutants and higher-order rowy1 rowy2 rowy3 triple mutants presented a wavy root growth phenotype. Cell biological experiments revealed that ROWY1 and PIN2 colocalized to the apical side of the plasma membrane in the root epidermis and that ROWYs are required for correct PM targeting of PIN2. In addition, ROWYs also affected PIN3 protein abundance in the stele, suggesting the potential involvement of additional PIN transporters as well as other proteins. A global transcriptome analysis revealed that ROWY genes are involved in the Fe2+ availability perception pathway. This work establishes ROWYs as important novel regulators of root gravitropic growth by connecting micronutrient availability to the proper subcellular targeting of PIN auxin transporters.

Ginseng rusty root symptoms result from nitric oxide stress in soil

Ginseng, from the roots of Panax ginseng C. A. Meyer, is a widely used herbal medicine in Asian countries, known for its excellent therapeutic properties. The growth of P. ginseng is depend on specific and strict environments, with a preference for wetness but intolerance for flooding. Under excessive soil moisture, some irregular rust-like substances are deposited on the root epidermis, causing ginseng rusty symptoms (GRS). This condition leads to a significant reduce in yield and quality, resulting in substantial economic loses. However, there is less knowledge on the cause of GRS and there are no effective treatments available for its treatment once it occurs. Unsuitable environments lead to the generation of large amounts of reactive oxygen species (ROS). We investigated the key indicators associated with the stress response during different physiological stages of GRS development. We observed a significant change in ROS level, MDA contents, antioxidant enzymes activities, and non-enzymatic antioxidants contents prior to the GRS. Through the analysis of soil features with an abundance of moisture, we further determined the source of ROS. The levels of nitrate reductase (NR) and nitric oxide synthase (NOS) activities in the inter-root soil of ginseng with GRS were significantly elevated compared to those of healthy ginseng. These enzymes boost nitric oxide (NO) levels, which in turn showed a favorable correlation with the GRS. The activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase first rose and then decreased as GRS developed. Excess soil moisture causes a decrease in oxygen levels. This activated NR and NOS in the soil, resulting in a production of excess NO. The NO then diffused into the ginseng root and triggered a burst of ROS through NADPH located on the cell membrane. Additionally, Fe2+ in soil was oxidized to red Fe3+, and finally led to GRS. This conclusion was also verified by the Sodium Nitroprusside (SNP), a precursor compound producing NO. The presence of NO from NR and NOS in water-saturated soil is responsible for the generation of ROS. Among these, NO is the main component that contribute to the occurrence of GRS.

β-Cyclodextrin enhanced bioavailability of petroleum hydrocarbons in industrially contaminated soil: A phytoremediation field study

Low remediation efficiency due to low bioavailability is a primary restrictive factor for phytoremediation applications. Specifically, this investigation examines whether Suaeda heteroptera Kitagawa (S. heteroptera) can be used in combination with β-cyclodextrin (β-CD) to remediate contaminated site. The study was conducted on the growth response of S. heteroptera, bioavailability and dissipation of petroleum hydrocarbons (PHs) in soil under the influence of β-CD Our preliminary studies confirmed that β-CD is effective in increasing the biomass and height of plants. The presence of β-CD could dramatically elevate polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in S. heteroptera. Moreover, a remarkable positive correlation between PHs levels in roots with the dosage of β-CD and a negative correlation between the PHs levels in roots with KOW of PHs have been observed. The dissipation of n-alkanes was estimated to be 38.73–62.27%, and the dissipation of PAHs was 36.59–60.10%. In addition, the dissipation behavior of n-alkanes and PAHs was well agreement with the first-order kinetic model. These results display that applying β-CD accelerated the desorption process of PHs from soil and promoted the absorption process of PHs onto the root epidermis. The enhancement of phytoremediation was achieved by increasing the bioavailability of PHs.

Mobility and growth in confined spaces are important mechanisms for the establishment of Bacillus subtilis in the rhizosphere.

The rhizosphere hosts complex and abundant microbiomes whose structure and composition are now well described by metagenomic studies. However, the dynamic mechanisms that enable micro-organisms to establish along a growing plant root are poorly characterized. Here, we studied how a motile bacterium utilizes the microhabitats created by soil pore space to establish in the proximity of plant roots. We have established a model system consisting of Bacillus subtilis and lettuce seedlings co-inoculated in transparent soil microcosms. We carried out live imaging experiments and developed image analysis pipelines to quantify the abundance of the bacterium as a function of time and position in the pore space. Results showed that the establishment of the bacterium in the rhizosphere follows a precise sequence of events where small islands of mobile bacteria were first seen forming near the root tip within the first 12-24 h of inoculation. Biofilm was then seen forming on the root epidermis at distances of about 700-1000 µm from the tip. Bacteria accumulated predominantly in confined pore spaces within 200 µm from the root or the surface of a particle. Using probabilistic models, we could map the complete sequence of events and propose a conceptual model of bacterial establishment in the pore space. This study therefore advances our understanding of the respective role of growth and mobility in the efficient colonization of bacteria in the rhizosphere.

Visualization of the Infection and Colonization Process of Dendrobium officinale Using a Green Fluorescent Protein-Tagged Isolate of Fusarium oxysporum.

Dendrobium officinale soft rot is a widespread and destructive disease caused by Fusarium oxysporum that can seriously affect yield and quality. To better understand the fungal infection and colonization, we successfully created an F. oxysporum labeled with green fluorescent protein using the Agrobacterium tumefaciens-mediated transformation method. Transformants had varying fluorescence intensities, but their pathogenicity did not differ from that of the wild type. Fluorescence microscopy revealed that F. oxysporum primarily entered the aboveground portion of D. officinale through the leaf margin, stomata, or by direct penetration of the leaf surface. It then colonized the mesophyll and spread along its vascular bundles. D. officinale exhibited typical symptoms of decay and wilting at 14 days postinoculation, accompanied by a pronounced fluorescence signal in the affected area. The initial colonization of F. oxysporum in the subterranean region primarily involved attachment to the root hair and epidermis, which progressed to the medullary vascular bundle. At 14 days postinoculation, the root vascular bundles of D. officinale exhibited significant colonization by F. oxysporum. Macroconidia were also observed in black rot D. officinale tissue. In particular, the entire root was surrounded by a significant number of chlamydospore-producing F. oxysporum mycelia at 28 days postinoculation. This approach allowed for the visualization of the complete infection process of F. oxysporum and provided a theoretical foundation for the development of field control strategies.

Investigating the Diversity in Physiological, and Molecular Responses of Wheat (Triticum aestivum L.) Genotypes under Cadmium Stress

Heavy metal toxicity is a real threat to the environment, crop productivity, and the health of humans and their animals, especially when the toxicity enters the food chain. This study investigates the effect of cadmium on the physiological and molecular levels of ten introduced wheat genotypes. Genotypes were stressed by cadmium (75 mg.L-1) in comparison with unstressed treatment to highlight their response to the cadmium. The experiment was laid out as a factorial arrangement in RCBD, with three replicates. The genotypes included in this study varied in their response to cadmium stress during the laboratory tests. Notably, genotype G-41 was superior to the rest of the genotypes in terms of seed vigor (18.58), chlorophyll content (8.72 mg.g-1), and carotenoid content (4.87 mg.g-1), while genotype IRAQ had wider epidermis in the root (2.28 µm) and ordinary epidermis cells (3.10 µm). Cadmium boosted some physiological and anatomical traits (e.g., REC, Chlorophyll, carotenoids, length and width of root epidermis cells). However, cadmium concentration caused a deterioration in some anatomical traits, including cortex thickness and the length of the ordinary epidermis cells. Some wheat genotypes showed more resistance to cadmium stress than others, and G-3 was notably affected by cadmium treatment and this was associated with the high PCS1 expression of the enzyme that chelates Cd to the vacuole (39 folds). It can be concluded that cadmium reduced the physiological performances except for some genotypes that showed more tolerance. Those genotypes could therefore be investigated further to assess the accumulation of cadmium in their grains.

Root hairs: an underexplored target for sustainable cereal crop production.

To meet the demands of a rising human population, plant breeders will need to develop improved crop varieties that maximize yield in the face of increasing pressure on crop production. Historically, the optimization of crop root architecture has represented a challenging breeding target due to the inaccessibility of the root systems. Root hairs, single cell projections from the root epidermis, are perhaps the most overlooked component of root architecture traits. Root hairs play a central role in facilitating water, nutrient uptake, and soil cohesion. Current root hair architectures may be suboptimal under future agricultural production regimes, coupled with an increasingly variable climate. Here, we review the genetic control of root hair development in the world's three most important crops-rice, maize, and wheat-and highlight conservation of gene function between monocots and the model dicot species Arabidopsis. Advances in genomic techniques including gene editing combined with traditional plant breeding methods have the potential to overcome many inherent issues associated with the design of improved root hair architectures. Ultimately, this will enable detailed characterization of the effects of contrasting root hair morphology strategies on crop yield and resilience, and the development of new varieties better adapted to deliver future food security.

Phenotypic characterization and culinary quality of cassava ethnovarieties cultivated in northern Mato Grosso, Brazil

Cassava (Manihot esculenta Crantz) has great importance as a food and serves as a raw material for various industrial products. The aim of this study was to evaluate phenotypic and culinary characteristics of the roots of 15 ethnovarieties of cassava sampled in northern Mato Grosso. The evaluated characteristics included root epidermis texture, skin color, cortex color and root pulp color before and after cooking, ease of removal of the skin and cortex, cooking time and aspects of the cooked mass. The ethnovarieties presented phenotypic diversity for the characteristics evaluated in their roots. The cooking time of cassava ethnovarieties cooked in a conventional pan ranged from 17 to 35 minutes. However, when the cooking of the ethnovarieties occurred in a pressure cooker, all were cooked within 10 minutes. The pressure cooker accelerated the cooking time considerably; however, it negatively influenced the aspects of the cooked mass and had greater water retention. The 15 cassava ethnovarieties present phenotypic variation regarding the texture and colors of the epidermis, cortex, skin, in the fresh pulp and after cooking. Such variation may be indicative of genetic variability, which suggests the need to conserve these cassava ethnovarieties. The evaluation of the culinary characteristics, considering the cooking time and the aspects of the cooked mass, showed that the ethnovarieties Cascatinha, Liberata, Branca 3, Folha roxa, Mandioca de fritar sem cozinhar, Branca 4, Amarelinha 2, Casca roxa, Amarelinha 3 and Casca branca are the most suitable for planting, consumption and commercialization, and can be harvested seven months after planting.

Modulation of abscisic acid signaling via endosomal TOL proteins.

The phytohormone abscisic acid (ABA) functions in the control of plant stress responses, particularly in drought stress. A significant mechanism in attenuating and terminating ABA signals involves regulated protein turnover, with certain ABA receptors, despite their main presence in the cytosol and nucleus, subjected to vacuolar degradation via the Endosomal Sorting Complex Required for Transport (ESCRT) machinery. Collectively our findings show that discrete TOM1-LIKE (TOL) proteins, which are functional ESCRT-0 complex substitutes in plants, affect the trafficking for degradation of core components of the ABA signaling and transport machinery. TOL2,3,5 and 6 modulate ABA signaling where they function additively in degradation of ubiquitinated ABA receptors and transporters. TOLs colocalize with their cargo in different endocytic compartments in the root epidermis and in guard cells of stomata, where they potentially function in ABA-controlled stomatal aperture. Although the tol2/3/5/6 quadruple mutant plant line is significantly more drought-tolerant and has a higher ABA sensitivity than control plant lines, it has no obvious growth or development phenotype under standard conditions, making the TOL genes ideal candidates for engineering to improved plant performance.

Observations of root hair patterning in soils: Insights from synchrotron-based X-ray computed microtomography

Abstract Background And Aims Root hair emergence is affected by heterogeneities in water availability in the growth medium. Root hairs preferentially emerge into air, whereas their emergence into water is inhibited. Yet, these results were based either on destructive methods or on roots grown on an agar-air interface. Additionally, there is a lack of knowledge about the spatial distribution of root hairs as hairs elongate radially across the rhizosphere. Therefore, root hair growth in soils remains largely unexplored. Methods Maize (Zea Mays L.) plants were grown in microcosms which were scanned with a synchrotron-based X-ray $$\mu $$ μ CT. The distribution of root hairs along the root epidermis and radially across the rhizosphere (i.e. as function of distance from the root epidermis) was analysed using spatial point pattern analysis. Results While hairs emerged randomly in air-filled pores, their emergence was inhibited where the root was in contact with the soil matrix. As hairs elongated radially into the soil, they were preferentially located in the close proximity of soil particles. In maize, we rarely observed root hairs penetrating into soil aggregates. Conclusion We conclude that in maize, root hairs grow in air-filled pores at the root-soil interface, where the flow of nutrients and water is impeded. Across the rhizosphere, hairs establish contact to the soil by growing in the proximity to soil particles. The effect of hairs on uptake processes, plant anchorage and rhizosheath formation might be limited (in maize) as they hardly penetrate into soil aggregates.

First Report of Monosporascus cannonballus causing Root Rot and Vine Decline in Watermelon (Citrullus lanatus) in China.

In June 2023, a sudden outbreak root rot and vine decline symptoms was observed during a watermelon (Citrullus lanatus T.) variety demonstration trial located in Taizhou City, Zhejiang Province, China, with an incidence rate ranging from 75% to 100% and an affected area of nearly 2,000 square meters. The disease initially appeared with a rapid and alarming invasion of root rot and vine decline symptoms within watermelon plants. Affected plants exhibited rapid deterioration, showing symptoms of wilting, yellowing and eventual demise, predominantly during the pre-harvest stage. Notably, numerous black, spherical, erumpent perithecia were clearly visible on the watermelon's root epidermis, a characteristic trait of the disease. Symptomatic plant samples were rigorously disinfected with 75% ethanol, and plated on potato dextrose agar medium for incubation at 25°C, successfully isolate two potential strains. These isolates were inoculated in oatmeal agar and incubated in a 25℃ light incubator. After 30 days, mature perithecia, the same as those found on the watermelon's root epidermis, reached a diameter of 500 μm. Each perithecium contained several pear-shaped asci, 56 to 108.5 μm in length and 30.5 to 46.4 μm in width, typically holding 1, rarely 2 ascospores. These characteristics align precisely with the typical strains of Monosporascus cannonballus Pollack and Uecker (1974). Additionally, sequencing the internal transcribed spacer region of ribosomal DNA (ITS) gene (White et al., 1990), large subunit ribosomal RNA (LSU) gene (Rehner and Samuels 1995), and beta-tubulin (TUB) gene (Glass and Donaldson, 1995) were performed. BLAST analysis indicated the highest nucleotide sequence identity with M. cannonballus CBS 586.93 reference sequence (ITS: 100%, JQ771930; TUB: 98.99%, JQ907292). Representative sequences of isolate ZJUP0990-2 from these regions were deposited in GenBank (Accession No.: OR357656 for ITS; OR474500 for LSU; OR365762 for TUB). A multigene phylogenomic analysis (ITS-LSU-TUB) was undertaken to ascertain the exact phylogenetic position of M. cannonballus within the genus Monosporascus. The amalgamation of both morphological and molecular insights consistently reaffirmed the accurate classification of the causative agent as M. cannonballus. To validate the pathogenicity of M. cannonballus, a controlled greenhouse experiment was conducted using watermelon (cv. Nabite) as the subject. Mycelium fragments, harvested from the edge of the colony ZJUP0990-2, were inoculated into oat liquid medium and cultivated under dark conditions at a consistent temperature of 30°C for 7 days. After 20 days, the inoculated plants exhibited root rot and wilting, mirroring the symptoms observed during the field outbreak. In contrast, the control plants did not exhibit any signs of disease. M. cannonballus was successfully re-isolated from the symptomatic roots of the inoculated plants, satisfying Koch's postulates. This experiment was repeated three times. This pathogenic fungus has previously been documented as a menace to melons in various regions including Mexico (Chew-Madinaveitia et al., 2012) and Brazil (Sales et al., 2004), as well as watermelons in Brazil (Sales et al., 2010), northern Mexico (Gaytan-Mascorro et al., 2012), and Saudi Arabia (Karlatti et al., 1997). To our knowledge, this is the first reported presence of M. cannonballus on watermelons in China. This new disease poses a serious threat to watermelon production, potentially leading to severe economic losses and impacting food security.

SbYS1 and SbWRKY72 regulate Cd tolerance and accumulation in sweet sorghum.

SbYS1 and its upstream transcription factor SbWRKY72 were involved in Cd tolerance and accumulation and are valuable for developing sweet sorghum germplasm with high-Cd tolerance or accumulation ability through genetic manipulation. Cadmium (Cd) is highly toxic and can severely affect human health. Sweet sorghum, as an energy crop, shows great potential in extracting cadmium from Cd-contaminated soils. However, its molecular mechanisms of Cd-tolerance and -accumulation remain largely unknown. Here, we isolated a YSL family gene SbYS1 from the sweet sorghum genotype with high Cd accumulation ability and the expression of SbYS1 in roots was induced by cadmium. GUS staining experiment exhibited that SbYS1 was expressed in the epidermis and parenchyma tissues of roots. Further subcellular localization analysis suggested that SbYS1 was localized in the endoplasmic reticulum and plasma membrane. Yeast transformed with SbYS1 exhibited a sensitive phenotype compared to the control when exposed to Cd-NA (chelates of cadmium and nicotianamine), indicating that SbYS1 may absorb cadmium in the form of Cd-NA. Arabidopsis overexpressing SbYS1 had a longer root length and accumulated less Cd in roots and shoots. SbWRKY72 bound to the promoter of SbYS1 and negatively regulated the expression of SbYS1. Transgenic Arabidopsis of SbWRKY72 showed higher sensitivity to cadmium and increased cadmium accumulation in roots. Our results provide references for improving the phytoremediation efficiency of sweet sorghum by genetic manipulation in the future.

Mechanism of salt tolerance in the endangered semi-mangrove plant Barringtonia racemosa: anatomical structure and photosynthetic and fluorescence characteristics.

To elucidate the mechanisms governing the salt tolerance of the endangered semi-mangrove plant Barringtonia racemosa, the biomass, photosynthetic and fluorescent characteristics, and anatomical structure of B. racemosa were studied under low, medium and high salt stress. The results showed that the stem dry weight, net photosynthetic rate, intercellular CO2 concentration, Fv/Fm, and ΦPSI of B. racemosa decreased under high salt stress, which led to a significant reduction in total dry weight. Stem dry weight was significantly positively correlated with the thickness of palisade tissue and significantly negatively correlated with the thickness of the epidermis of roots and xylem of stems. Therefore, a stable net photosynthetic rate and intercellular CO2 concentration, an increase in Fv/Fm and ΦPSI, an increase in or stable palisade tissue and spongy mesophyll of leaves and an increase in xylem thickness of the stem and epidermis, outer cortex, and stele diameter of roots could contribute to the salt tolerance of B. racemosa.

Arbuscular Mycorrhizal Fungus Alleviates Charged Nanoplastic Stress in Host Plants via Enhanced Defense-Related Gene Expressions and Hyphal Capture.

Contamination of small-sized plastics is recognized as a factor of global change. Nanoplastics (NPs) can readily enter organisms and pose significant ecological risks. Arbuscular mycorrhizal (AM) fungi are the most ubiquitous and impactful plant symbiotic fungi, regulating essential ecological functions. Here, we first found that an AM fungus, Rhizophagus irregularis, increased lettuce shoot biomass by 25-100% when exposed to positively and negatively charged NPs vs control, although it did not increase that grown without NPs. The stress alleviation was attributed to the upregulation of gene expressions involving phytohormone signaling, cell wall metabolism, and oxidant scavenging. Using a root organ-fungus axenic growth system treated with fluorescence-labeled NPs, we subsequently revealed that the hyphae captured NPs and further delivered them to roots. NPs were observed at the hyphal cell walls, membranes, and spore walls. NPs mediated by the hyphae were localized at the root epidermis, cortex, and stele. Hyphal exudates aggregated positively charged NPs, thereby reducing their uptake due to NP aggregate formation (up to 5000 nm). This work demonstrates the critical roles of AM fungus in regulating NP behaviors and provides a potential strategy for NP risk mitigation in terrestrial ecosystems. Consequent NP-induced ecological impacts due to the affected AM fungi require further attention.

Response of Typha domingensis during an accidental discharge of high Cr(VI) concentration in a full-scale treatment wetland

This work assesses the Cr accumulation and tolerance of Typha domingensis after an accidental discharge of wastewater that produced a concentration of Cr(VI) of approximately 120 mg L−1 in a free-water surface wetland. The wetland was constructed for the final wastewater treatment of a metallurgical manufacturing plant. It is 7 m wide, 20 m long, and waterproofed with a geomembrane. A 1.5 m soil layer was placed on top of the geomembrane. Water, plants, and sediment were sampled before and after an accidental discharge. The root anatomical measurements of the plants from the treatment wetland were compared with those of plants from an uncontaminated wetland (control). Roots and dead leaves from the inlet plants showed the highest Cr concentrations after the accidental discharge (12.4 and 11.6 mg g−1, respectively). SEM-EDX mapping determined that Cr was accumulated in root epidermis. Cr accumulation in plant detritus, plant roots, and sediment were the mechanisms for Cr removal. Plants accumulated Cr in belowground tissues demonstrating their potential for phytostabilization. T. domingensis was capable of modifying its morphology to respond to high Cr concentrations. This macrophyte is a suitable species for wetlands constructed for the treatment of a wastewater with high Cr(VI) concentration. The studied system was capable of minimizing the impact and preserving the environment.

Biosynthesis of polyhydroxybutyrate by Methylorubrum extorquens DSM13060 is essential for intracellular colonization in plant endosymbiosis.

Methylorubrum extorquens DSM13060 is an endosymbiont that lives in the cells of shoot tip meristems. The bacterium is methylotrophic and consumes plant-derived methanol for the production of polyhydroxybutyrate (PHB). The PHB provides protection against oxidative stress for both host and endosymbiont cells through its fragments, methyl-esterified 3-hydroxybutyrate (ME-3HB) oligomers. We evaluated the role of the genes involved in the production of ME-3HB oligomers in the host colonization by the endosymbiont M. extorquens DSM13060 through targeted genetic mutations. The strains with deletions in PHB synthase (phaC), PHB depolymerase (phaZ1), and a transcription factor (phaR) showed altered PHB granule characteristics, as ΔphaC had a significantly low number of granules, ΔphaR had a significantly increased number of granules, and ΔphaZ1 had significantly large PHB granules in the bacterial cells. When the deletion strains were exposed to oxidative stress, the ΔphaC strain was sensitive to 10 mM HO· and 20 mM H2O2. The colonization of the host, Scots pine (Pinus sylvestris L.), by the deletion strains varied greatly. The deletion strain ΔphaR colonized the host mainly intercellularly, whereas the ΔphaZ1 strain was a slightly poorer colonizer than the control. The deletion strain ΔphaC lacked the colonization potential, living mainly on the surfaces of the epidermis of pine roots and shoots in contrast to the control, which intracellularly colonized all pine tissues within the study period. In earlier studies, deletions within the PHB metabolic pathway have had a minor effect on plant colonization by rhizobia. We have previously shown the association between ME-3HB oligomers, produced by PhaC and PhaZ1, and the ability to alleviate host-generated oxidative stress during plant infection by the endosymbiont M. extorquens DSM13060. Our current results show that the low capacity for PHB synthesis leads to poor tolerance of oxidative stress and loss of colonization potential by the endosymbiont. Altogether, our findings demonstrate that the metabolism of PHB in M. extorquens DSM13060 is an important trait in the non-rhizobial endosymbiosis.

Spatial IMA1 regulation restricts root iron acquisition on MAMP perception.

Iron is critical during host-microorganism interactions1-4. Restriction of available iron by the host during infection is an important defence strategy, described as nutritional immunity5. However, this poses a conundrum for externally facing, absorptive tissues such as the gut epithelium or the plant root epidermis that generate environments that favour iron bioavailability. For example, plant roots acquire iron mostly from the soil and, when iron deficient, increase iron availability through mechanisms that include rhizosphere acidification and secretion of iron chelators6-9. Yet, the elevated iron bioavailability would also be beneficial for the growth of bacteria that threaten plant health. Here we report that microorganism-associated molecular patterns such as flagellin lead to suppression of root iron acquisition through a localized degradation of the systemic iron-deficiency signalling peptide Iron Man 1 (IMA1) in Arabidopsis thaliana. This response is also elicited when bacteria enter root tissues, but not when they dwell on the outer root surface. IMA1 itself has a role in modulating immunity in root and shoot, affecting the levels of root colonization and the resistance to a bacterial foliar pathogen. Our findings reveal an adaptive molecular mechanism of nutritional immunity that affects iron bioavailability and uptake, as well as immune responses.

Diversity of 17 Genotypes of Taro Based on Anatomy and Nutritional Value of Tuber

Indonesia is one of the countries with the greatest diversity of taro variety, while the study of taro's morphology and nutritional characteristics is limited. The aim of this study was to evaluate the anatomical of plant and nutritional value of taro tuber. This research observed fourteen genotypes of Colacasia esculenta (7 Eddoe types, 7 Dasheen types) and 3 Xanthosoma genotypes. In three blocks of replications, the eddoe and Xanthosoma genotypes were cultivated using cormel and the dasheen genotypes with sucker. Plant anatomy (leaf, stem, and root) and tuber nutritional characteristics were analyzed. From this research, explained that stomata and epidermis number, length from stomata and epidermis, number leaf epidermis, length of leaf and stem epidermis, also length of root epidermis, endodermis, cortex, and stele among 17 genotypes of taro were statistically different. The diversity of taro based on the nutrition content of tuber between 17 genotypes of taro was considered high, as represented by water, ash, fat, protein, carbohydrate, energy, and glucomannan, which were statistically different.