Internal Plant Tissues Research Articles

A new method for the direct tracking of in vivo lignin nanocapsules in Eragrostis tef (Poaceae) tissues.

Environmental concerns have driven scientists to research new eco-friendly approaches for the preparation of nanosystems. For this purpose, novel bio-polymers have been selected. Among these, one of the most promising is lignin, which is biodegradable and biocompatible. Additionally, lignin is one of the main by-products of the paper industry and can be re-used in nanosystems building. Lignin-based nanosystems could be used in agriculture, to improve the uptake of bioactive compounds, thus avoiding soil pollution. However, the mechanism of penetration in the plant and the route of transportation within the internal plant tissues are unknown and need to be clearly elucidated. Here we present a method of lignin nanocapsules staining and tracking by fluorochrome: Fluoral Yellow 088, which is a well-suited dye for the tracking of lipids and other oil phases. Two different applications were applied: in the first one fourteen-day plants were soaked with fluorescent nanocapsules (fNCs) pure solution and in the second one, Eragrostis tef plants were laid down on blotting paper and soaked with diluted fNCs solution. Wetting the roots of Teff plantlets with the pure fNCs solution resulted in the most efficient way of nanocapsule entrance. The dyeing of lignin nanocapsules allowed us to track them in Eragrostis tef plant tissues through microscopic observations. In particular, fNCs were proven to be able to permeate roots, reaching xylem vessels where, through water pressure, they reached the leaf.

Diversity of the bacteria in the roots of sugarcane used to produce Wasanbon in Kagawa, Japan.

Soil bacteria are an important factor in the cycle of nutrients in soil, while root bacteria in the internal tissues of plants can promote plant growth. The aim of this research was to study the diversity of root bacteria of sugarcane grown in Kagawa, Japan. The sugarcane, derived from Saccharum sinense and grown only in this area, is used as a raw material for Wasanbon (a fine-grained Japanese sugar) and is characterized by thin stalks and a low sugar content. To determine its bacterial diversity, bacterial DNA was extracted from the soil and roots, and 16S rRNA genes were sequenced. A total of 1259 operational taxonomic units (OTUs) were detected in the root bacteria and 3894 OTUs in the soil bacteria. The α-diversity between the soil and root bacteria was significantly different. The most abundant class of root and soil bacteria was proteobacteria at more than 50 and 30%, respectively. The endophyte bacteria of rhizobium were also isolated and the nifH gene was detected. The relationship between the application of nitrogen-fixing bacteria and the production of Wasanbon should be studied.

Endophytic Bacteria isolated from the leaf of Langusei (Ficus minahassae Tesym. & De Vr.) and their antibacterial activities

Endophytic bacteria colonizing the internal tissues of plants are being studied for its potential beneficial properties including antibacterial activity. The aims of this study were to identify the endophytic bacteria residing in the leaf of Ficus minahassae, a native plant of North Sulawesi, as well as their antibacterial activities against laboratory-adapted reference bacterial strains, Staphylococcus aureus, and Escherichia coli. The isolate identification was conducted using the 16S rRNA gene marker and the antibacterial activity test was done using a well diffusion method. A yellow-pigmented (designated as YL1) and a beige-pigmented (designated as YL2) bacteria were isolated from the internal tissue of langusei. Using the BLAST search, the isolate YL1 had a 100% identity with Brachybacterium muris, while YL2 has 99% identity with Pseudacidovorax intermedius. Ez-Taxon database confirmed that YL1 was B. muris with 99.81% similarity, while YL2 was P. intermedius with 99.80% similarity. Isolate YL2 was able to inhibit the growth of S. aureus but not E. coli. Isolate YL1 did not inhibit both reference bacteria. This study represents the first investigation of endophytic bacteria isolated from langusei leaf and their antibacterial activity.

Unearthing the Plant Growth-Promoting Traits of Bacillus megaterium RmBm31, an Endophytic Bacterium Isolated From Root Nodules of Retama monosperma.

Plants live in association with complex populations of microorganisms, including Plant Growth-Promoting Rhizobacteria (PGPR) that confer to plants an improved growth and enhanced stress tolerance. This large and diverse group includes endophytic bacteria that are able to colonize the internal tissues of plants. In the present study, we have isolated a nonrhizobial species from surface sterilized root nodules of Retama monosperma, a perennial leguminous species growing in poor and high salinity soils. Sequencing of its genome reveals this endophytic bacterium is a Bacillus megaterium strain (RmBm31) that possesses a wide range of genomic features linked to plant growth promotion. Furthermore, we show that RmBm31 is able to increase the biomass and positively modify the root architecture of seedlings of the model plant species Arabidopsis thaliana both in physical contact with its roots and via the production of volatile organic compounds. Lastly, we investigated the molecular mechanisms implicated in RmBm31 plant beneficial effects by carrying out a transcriptional analysis on a comprehensive set of phytohormone-responsive marker genes. Altogether, our results demonstrate that RmBm31 displays plant growth-promoting traits of potential interest for agricultural applications.

Characterization of Endophytic Microbial Communities in Store-Bought Kale Evaluated by Different Plant Tissue Homogenization Methods

Endophytic microorganisms live in intercellular and vascular spaces of plants and span the continuum from beneficial to pathogenic in both plants and animals. Increasing human consumption of fruits and vegetables has placed an emphasis on identifying and studying those microbes that colonize the internal tissues of plants, with a goal of limiting populations of enteric pathogens in store-bought foods meant for raw consumption, such as leafy greens. Culture-independent (i.e., metagenomic) methods are increasingly used to obtain an accurate snapshot of plant microbial communities, yet technical hurdles limit the accuracy and throughput of these methods. This includes the low-throughput nature of plant tissue maceration, and the prevalence of plant plastid DNA in metagenomic DNA extracts, which is typically coamplified via PCR strategies that target the bacterial 16S rRNA gene. In this study, we use kale (Brassica oleracea) as a model to explore the leafy green endophytic microbiome and to compare how two tissue maceration techniques used in traditional endophyte research compare in culture-independent microbiome studies using the Illumina Miseq platform. Three different brands of store-bought kale were surface sterilized and subjected to two tissue maceration strategies: enzyme digestion and blender processing. Analysis of 16S rRNA gene amplicon libraries revealed two highly abundant operational taxonomic units present in all libraries, one classified to the genus Pseudomonas and one to the family Enterobacteriaceae. Community structure and membership were highly similar among brands and between tissue maceration strategies, suggesting that both enzyme digestion and blender processing are suitable methods. Nonetheless, enzyme digestion may increase sample throughput and minimize steps involved in sample processing.

Comparative analysis of endophytic bacterial diversity between two varieties of sunflower Helianthus annuus with their PGP evaluation.

Endophytic bacterial diversity shows an intricate network of interactions with host plants as they reside in various tissues and organs at certain stages or all stages of their life cycle stimulating the plant growth and fitness. Sunflower is a trendy oilfield crop and variation in its varieties is associated with the dynamics of endophytic diversity. The present study is undertaken to identify and compare the ecological niche of endophytic bacterial communities amongst different tissues of two hybrids varieties Hysun-33 and Hysun-39 of sunflower (Helianthus annuus) at three developmental stages which are vegetative stage I (after 15 days of seeds germination), vegetative stage II (after 30 days of germination) and reproductive stage (after 90 days of germination). A total of 74 endophytes from Hysun-33 and 115 endophytes from Hysun-39 have been isolated from different tissues and growth stages. Amongst plant parts, root tissues harbored higher bacterial inhabitants (44) followed by stem (33), leaf (30) and flower (7) of Hysun-39. Likewise, Hysun-33 endophytes colonized roots more abundantly followed by leaves, stem and flowers. All strains are found to be gram positive with the exception of only RA9 from Hysun-33 and RB9 from Hysun-39 that are gram negative. Among different growth stages, the maximum bacterial population (CFU of 320 × 103) was found amongst root microflora at vegetative stage II of plant in Hysun-39 variety as compared to root endophytes of Hysun-33 having (CFU of 10 × 103). The evaluation of their growth promoting features revealed that among 74 isolates of Hysun-33, 70% exhibited the ability of hydrogen cyanide production, 43% IAA production, 36% siderophore production and 4% nitrogen fixation and also phosphate solubilization. However among 115 isolates of Hysun-39, 64% appeared as hydrogen cyanide producers, 56% IAA producers, 33% siderophore producers, 2% nitrogen fixers and 4% as phosphate solubilizers. Therefore our study reveals understanding of wide-ranging diversity of endophytic bacteria and their beneficial relationship with internal tissues of host plant which may recommend their implementation to crops for better development of agricultural systems.

Biochemical and molecular identification of Solanum lycopersicum L. temperature tolerant bacterial endophytes

Abstract Endophytes are non-pathogenic microorganisms and potential natural bio-inoculant that reside within internal tissues of plant, without causing any apparent symptoms of infection and improve the plant health through acquisition of nutrients. The endophytic bacteria were isolated from the roots of Solanum lycopersicum L. surviving at 45–47 °C in the month of June 2013. On the basis of morphological, biochemical, carbon utilization pattern by Biolog and 16S rRNA gene sequence analysis, the isolates were identified as Rhizobium pusense (MS-1), Bacillus flexus (MS-2), B. cereus (MS-3), Methylophilus flavus (MS-4) and Pseudomonas aeruginosa (MS-5). Most of the endophytic bacterial strains showed plant growth promoting traits activities such as phosphate solubilization, production of IAA, siderophore, ammonia, and nitrate reductase. Carbon sources and other chemicals utilization pattern observed with GEN III microplate of Biolog exhibited strains specific responses. Ten antibiotics discs and 96 wells PM 11C plates were used for their antibiotic sensitivity assay. All the strains were sensitive to chloramphenical, erythromycin, rifampicin, piperacillin, imipenam and gentamycin, while P. aeruginosa (MS-5) was resistant to penicillin, linezolid, and clotrimazole discs. This is first report of M. flavus, a facultative methylotroph as an endophyte of tomato plant.

Isolation and Characterization of Nodule Endophytes from Bunching and Semi-spreading Groundnut Genotypes

Bacterial endophytes prevalently colonize the internal tissues of plants and are shown to positively influence plant growth. They play a significant role in maximizing crop productivity while reducing the environmental impacts of agriculture. The aim of the present work was to isolate and characterize root nodule endophytes from two groundnut genotypes (Bunching & Semispreading). A total of 20 bacterial isolates were recovered from groundnut nodules using the yeast extract mannitol agar medium supplemented with congo red. The isolates were characterized morphologically, biochemically and compared with the reference strains Rhizobium sp. TNAU 14, Rhizobium sp. COS 1 and Bradyrhizobium sp. The isolates showed close similarity to the reference strains in their biochemical and morphological characteristics. Based on these results, it is concluded that the isolates YBB1, YBB6, YBB8, YBB14A, S27 from the bunching type and YSB 3, YSB4 and YSB5 from the semi-spreading genotype tentatively represent Rhizobium. .

Use of antibiotics to control endophytic bacterial growth migration onto culture medium in Eucalyptus cloeziana F.Muell.: a micropropagation approach

The natural endophytic bacterial growth migration onto a culture medium is commonly associated with unnecessary microplant discards. In micropropagation procedures, some bacteria can exude from the internal tissues of plants to colonize the culture medium and compete with the plants for nutrients, which may lead to a reduction in plant development. To find an efficient antibiotic protocol to control this bacterial growth migration onto the culture medium without affecting plant development, Eucalyptus cloeziana F.Muell. microstumps were subjected to four antibiotic treatments for 30 d. They were treated with gentamicin, ciprofloxacin, rifampicin, or Timentin®, in addition to the control treatment (antibiotic free). The effects of the antibiotics were monitored weekly, and the endophytic bacterial community structures were evaluated in two periods of plant development (15 d and 30 d).The denaturing gradient gel electrophoresis (DGGE) technique was used to compare the control and post-antibiotic treatment plant microbiological composition, to determine if the antibiotic treatment played a specific role on the endophytic bacterial community structure. The gentamicin treatment was composed of a distinct community from the control treatment. Nonetheless, the plants treated with ciprofloxacin and rifampicin manifested similar endophytic community structures compared to the control. In contrast, plants treated with Timentin® showed a specific bacterial community composition and a higher plant dry mass, number of shoots, and nutritional content. These results suggested that Timentin® treatment could be applied for 30 days to control endophytic bacterial growth migration onto the culture medium, without affecting the homeostatic balance between the bacteria and plants.

Bacillus Spp.: Efficient Biotic Strategy to Control Postharvest Diseases of Fruits and Vegetables.

Postharvest diseases significantly reduce the shelf-life of harvested fruits/vegetables worldwide. Bacillus spp. are considered to be an eco-friendly and bio-safe alternative to traditional chemical fungicides/bactericides due to their intrinsic ability to induce native anti-stress pathways in plants. This review compiles information from multiple scientific databases (Scopus, ScienceDirect, GoogleScholar, ResearchGate, etc.) using the keywords “postharvest diseases”, “Bacillus”, “Bacillus subtilis”, “biocontrol”, “storage”, “losses”, and “fruits/vegetables”. To date, numerous examples of successful Bacillus spp. application in controlling various postharvest-emerged pathogens of different fruits/vegetables during handling, transportation, and storage have been described in the literature. The mechanism/s of such action is/are still largely unknown; however, it is suggested that they include: i) competition for space/nutrients with pathogens; ii) production of various bio-active substances with antibiotic activity and cell wall-degrading compounds; and iii) induction of systemic resistance. With that, Bacillus efficiency may depend on various factors including strain characteristics (epiphytes or endophytes), application methods (before or after harvest/storage), type of pathogens/hosts, etc. Endophytic B. subtilis-based products can be more effective because they colonize internal plant tissues and are less dependent on external environmental factors while protecting cells inside. Nevertheless, the mechanism/s of Bacillus action on harvested fruits/vegetables is largely unknown and requires further detailed investigations to fully realize their potential in agricultural/food industries.

Induction of tolerance to salinity in wheat genotypes by plant growth promoting endophytes: Involvement of ACC deaminase and antioxidant enzymes

Plant growth-promoting endophytes (PGPEs) can colonize the internal tissues of plants and are capable of promoting plant growth. These bacteria can improve plant tolerance against various biotic and abiotic stresses via the expression of antioxidant enzymes and the production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Two salt-tolerant PGPEs, Kocuria rhizophila: KF875448 (14ASP) and Cronobacter sakazakii: KM042090 (OF115), with ACC deaminase activity were investigated for their potential to ameliorate plant salinity stress. The wheat varieties Pasban 90 and Khirman were subjected to two levels of salt stress (80 and 160 mM NaCl) under greenhouse conditions by using a completely randomized design. Analyses of plant growth parameters, antioxidant enzyme activities, chlorophyll and plant mineral contents were conducted to investigate the stress tolerance induced by the PGPEs. The ACC utilization by the PGPEs directly relates to the promotion of plant growth due to the lowering of excess ethylene production under salt stress. High levels of NaCl exhibited negative effects in both varieties. However, inoculation with PGPEs increased the morphological traits and antioxidant activities of the plants while decreasing the Na+ contents in all treatments compared to uninoculated treatment. Wheat variety Pasban 90 was more tolerant than Khirman in to salt stress in all the measured morphological and biochemical parameters, while the bacterial strain OF115 performed significantly better in all morphological and biochemical parameters, such as fresh dry weight, root shoot length, proline and chlorophyll contents, compared to strain 14ASP. The K+/Na+ ratio in the tissues of bacterial treated plants was higher than the control, probably in order to maintain the nutrient balance. The results of our study revealed that the inoculation of plants by ACC deaminase-producing PGPEs is a potential tool for the enhancement of plant growth and stress tolerance. Moreover, endophytic bacteria allied with host plants are capable of enduring high saline conditions and can interact with plants in a very efficient way.

FUNGAL ENDOPHYTES AS REPOSITORY OF XANTHINE OXIDASE INHIBITOR

Xanthine oxidase, a key enzyme of purine metabolism, is considered to be a prime target for the treatment of hyperuricemia and oxidative stress related disorders. Allopurinol and febuxostat are two FDA approved xanthine oxidase inhibitors currently being used for management of chronic hyperuricemia. Plethora of natural sources has been explored in search of novel chemical templates for the development of antihyperuricemic drugs. Studies in past decade have shown the potential of endophytic fungi, which colonize the internal tissues of plants without any evident sign of their ubiquitous existence, as repository of novel chemical entities exhibiting antimicrobial, anti-oxidant, anti-inflammatory and anticancer potential. However, very scanty preliminary data is available of exploration of xanthine oxidase inhibitors from fungal endophytes. The present review summarizes the efficacy of xanthine oxidase as target for developing ant-gout agents and highlights the prospective of endophytic fungi as producers of xanthine oxidase inhibitors for the anti-hyperuricemic therapy regimen.

Mycovirus Fusarium oxysporum f. sp. dianthi Virus 1 Decreases the Colonizing Efficiency of Its Fungal Host.

Mycoviruses that induce hypovirulence in phytopathogenic fungi are interesting because their potential use as biological control agents of the plant diseases caused by their fungal hosts. The recently identified chrysovirus Fusarium oxysporum f. sp. dianthi virus 1 (FodV1) has been associated to the induction of hypovirulence in Fusarium oxysporum f. sp. dianthi, the forma specialis of F. oxysporum that causes vascular wilt in carnation (Dianthus caryophyllus). In this work, we have used confocal laser scanner microscopy and two isogenic GFP-labeled strains of F. oxysporum f. sp. dianthi infected (V+) and not infected (V−) with the Fusarium oxysporum f. sp. dianthi virus 1, respectively, to analyze the effect of mycovirus FodV1 on the plant colonization pattern of its fungal host. Results demonstrate that FodV1-viral infection affects the speed and spatial distribution of fungal colonization into the plant. Initial stages of external root colonization were similar for both strains, but the virus-free strain colonized the internal plant tissues faster than the virus-infected strain. In addition, other differences related to the specific zone colonized and the density of colonization were observed between both F. oxysporum f. sp. dianthi strains. The hyphae of both V− and V+ strains progressed up through the xylem vessels but differences in the number of vessels colonized and of hyphae inside them were found. Moreover, as colonization progressed, V− and V+ hyphae propagated horizontally reaching the central medulla but, while the virus-free strain V− densely colonized the interior of the medulla cells, the virus-infected strain V+ appeared mainly in the intercellular spaces and with a lower density of colonization. Finally, the incidence of FodV1-viral infections in a collection of 221 isolates sampled between 2008 and 2012 in the geographic area where the originally infected isolate was obtained has been also analyzed. The very low (<2%) incidence of viral infections is discussed here. To the best of our knowledge, this work provides the first microscopic evidence about the effect of a hypovirulence-inducing mycovirus on the pattern of plant colonization by its fungal host.

Isolation and Characterization of Endophytic Bacteria from Piper longum

Endophytes are non-pathogenic microorganisms that reside within internal tissues of plant, without causing any apparent symptoms of infection. In an attempt to identify endophytes from Piper longum, the Indian long pepper, a combination of conventional and molecular approaches was used. Using culture-dependent approach, six different bacterial isolates were obtained from various surface-sterilized parts (roots, nodes, internodes, petioles, leaves and spikes) of the plant. In general, roots harboured maximum concentration of endophytic bacterial isolates, while leaves contained the minimum levels. These endophytes were analyzed on the basis of colony morphology and biochemical characteristics. Based on the results obtained after BLAST search of 16S rDNA sequence in NCBI database, the endophytes isolated from Piper longum showed highest similarity to Endophytic bacteria 135L-3, Enterobacter sp. SQ6-43, Bacillus casamancensis strain TN3, Alishewanella sp. JS-30, Bacterium B28 and Enterobacter ludwigii strain g45. Most of the identified bacteria belong to the phylum Proteobacteria and Firmicutes, whose members have been reported to act as growth-promoting bacteria in other plant species. Some of these endophytes tested positive for the ability to produce indole-3-acetic acid and hydrogen cyanide, suggesting their potential roles in plant growth promotion and biological control against pathogens, respectively.

Exploring potential of bacterial endophytes in disease management of horticultural crops

The endophytes are facultative or obligate symbiotic microorganisms, living in apparently healthy internal plant tissues, without causing disease in the host. Bacterial endophytes are found in a diverse group of plants including many horticultural crops, viz. fruits, flowers and medicinal plants. They harbour diverse group of bacterial endophytes including members of Pseudomonads, Bacillus and Streptomyces, which have been found successful against many phytopathogenic fungi and bacteria. Endophytes can suppress diseases through various mechanisms, viz. antibiosis, competion, lysis, siderophore production, enhanced host defense etc. Many Actinobacteria produce metabolites with antimicrobial activity which can be explored as a potential alternative to chemical in plant disease management. Moreover, bacterial endophytes have been reported to play a crucial role in bioremediation of organic and inorganic pollutants and promoting plant growth through nutrient enhanced nutrient uptake.

Multifaceted Interactions Between Endophytes and Plant: Developments and Prospects.

Microbial endophytes are present in all known plant species. The ability to enter and thrive in the plant tissues makes endophytes unique, showing multidimensional interactions within the host plant. Several vital activities of the host plant are known to be influenced by the presence of endophytes. They can promote plant growth, elicit defense response against pathogen attack, and can act as remediators of abiotic stresses. To date, most of the research has been done assuming that the interaction of endophytes with the host plant is similar to the plant growth-promoting (PGP) microbes present in the rhizosphere. However, a new appreciation of the difference of the rhizosphere environment from that of internal plant tissues is gaining attention. It would be interesting to explore the impact of endosymbionts on the host’s gene expression, metabolism, and other physiological aspects essential in conferring resistance against biotic and abiotic stresses. A more intriguing and inexplicable issue with many endophytes that has to be critically evaluated is their ability to produce host metabolites, which can be harnessed on a large scale for potential use in diverse areas. In this review, we discuss the concept of endophytism, looking into the latest insights related to the multifarious interactions beneficial for the host plant and exploring the importance of these associations in agriculture and the environment and in other vital aspects such as human health.

Assessment of bacterial inoculant formulated with Paraburkholderia tropica to enhance wheat productivity.

Paraburkholderia tropica is an endophytic nitrogen-fixing bacterium isolated from the rhizosphere, rhizoplane, and internal tissues of sugarcane and corn plants in different geographical regions. Other plant-growth-promoting abilities, such as phosphate solubilization and antifungal activity, have also been reported for this bacterium. With an aim at investigating the potential use of P. tropica as an inoculant for improving the performance of wheat crop, in this work we evaluated an experimental inoculant formulated with P. tropica MTo-293 with respect to root colonization, the practical aspects of its application, and the effects under field conditions when applied to wheat seeds. Bacterial colonization was monitored by culture dependent techniques and the wheat yield determined by quantifying the total grain production in two different seasons. Rhizoplane and endophytic colonization in wheat roots was achieved efficiently (on average, 8 and 4 log colony-forming units/g fresh weight, respectively) even at relatively low concentrations of viable bacteria in the inoculum under controlled conditions. P. tropica was compatible with a widely used fungicide, maintained viability for 48h once applied to seeds, and was also able to colonize wheat roots efficiently. Furthermore, we were able to formulate an inoculant that maintained bacterial viability for relatively long time periods. Preliminary field assays were realized, and even though the average yields values for the inoculated treatments remained above the uninoculated ones, no significant effects of inoculation were detected with or without fertilization. The correct physiologic behavior of P. tropica suggests the necessity to continue with field experiments under different conditions.

Endophytic Metarhizium brunneum mitigates nutrient deficits in potato and improves plant productivity and vitality

Abstract There is growing evidence that entomopathogenic fungi play a role in plant growth promotion as colonizers of internal plant tissues. However, little is known about their potential to mitigate plant abiotic stress. Here, we investigated the influence of soil fertility on Metarhizium brunneum strain CB15 endophytism levels in potato plants linked to plant productivity and vitality. By application of encapsulated M. brunneum, the endophytism level, i.e. % presence of fungus in plant tissue, increased significantly under nutrient poor conditions. This correlated with significantly improved quantum yields of photosystem II. In addition, water use efficiency was increased with higher levels of M. brunneum endophytism. Furthermore, biomass, leaf area, nitrogen and phosphorus contents were enhanced indicating fungal nutrient mobilization and transfer. Our results provide first evidence for the role of entomopathogenic fungi in mitigating nutrient deficits in soil by improving plant productivity and vitality which may increase their use in plant protection strategies.

A dual role for proline iminopeptidase in the regulation of bacterial motility and host immunity.

During plant-pathogen interactions, pathogenic bacteria have evolved multiple strategies to cope with the sophisticated defence systems of host plants. Proline iminopeptidase (PIP) is essential to Xanthomonas campestris pv. campestris (Xcc) virulence, and is conserved in many plant-associated bacteria, but its pathogenic mechanism remains unclear. In this study, we found that disruption of pip in Xcc enhanced its flagella-mediated bacterial motility by decreasing intracellular bis-(3',5')-cyclic dimeric guanosine monophosphate (c-di-GMP) levels, whereas overexpression of pip in Xcc restricted its bacterial motility by elevating c-di-GMP levels. We also found that PIP is a type III secretion system-dependent effector capable of eliciting a hypersensitive response in non-host, but not host plants. When we transformed pip into the host plant Arabidopsis, higher bacterial titres were observed in pip-overexpressing plants relative to wild-type plants after Xcc inoculation. The repressive function of PIP on plant immunity was dependent on PIP's enzymatic activity and acted through interference with the salicylic acid (SA) biosynthetic and regulatory genes. Thus, PIP simultaneously regulates two distinct regulatory networks during plant-microbe interactions, i.e. it affects intracellular c-di-GMP levels to coordinate bacterial behaviour, such as motility, and functions as a type III effector translocated into plant cells to suppress plant immunity. Both processes provide bacteria with the regulatory potential to rapidly adapt to complex environments, to utilize limited resources for growth and survival in a cost-efficient manner and to improve the chances of bacterial survival by helping pathogens to inhabit the internal tissues of host plants.

Soft Tendril-Inspired Grippers: Shape Morphing of Programmable Polymer-Paper Bilayer Composites.

Nastic movements in plants that occur in response to environmental stimuli have inspired many man-made shape-morphing systems. Tendril is an exemplification serving as a parasitic grasping component for the climbing plants by transforming from a straight shape into a coiled configuration via the asymmetric contraction of internal stratiform plant tissues. Inspired by tendrils, this study using a three-dimensional (3D) printing approach developed a class of soft grippers with preprogrammed deformations being capable of imitating the general motions of plant tendrils, including bending, spiral, and helical distortions for grasping. These grippers initially in flat configurations were tailored from a polymer-paper bilayer composite sheet fabricated via 3D printing a polymer on the paper substrate with different patterns. The rough and porous paper surface provides a printed polymer that is well-adhered to the paper substrate which in turn serves as a passive strain-limiting layer. During printing, the melted polymer filament is stretched, enabling the internal strain to be stored in the printed polymer as memory, and then it can be thermally released, which will be concurrently resisted by the paper layer, resulting in various transformations based on the different printed geometries. These obtained transformations were then used for designing grippers to grasp objects with corresponding motions. Furthermore, a fully equipped robotic tendril with three segments was reproduced, where one segment was used for grasping the object and the other two segments were used for forming a tendril-like twistless spring-like structure. This study further helps in the development of soft robots using active polymer materials for engineered systems.