Root-knot nematode chemotaxis is positively regulated by l-galactose sidechains of mucilage carbohydrate rhamnogalacturonan-I

Disruption of the Arabidopsis Acyl-Activating Enzyme 3 Impairs Seed Coat Mucilage Accumulation and Seed Germination

The Acyl-activating enzyme (AAE) 3 gene encodes an oxalyl-CoA synthetase that catalyzes the conversion of oxalate to oxalyl-CoA as the first step in the CoA-dependent pathway of oxalate catabolism. Although the role of this enzyme in oxalate catabolism has been established, its biological roles in plant growth and development are less understood. As a step toward gaining a better understanding of these biological roles, we report here a characterization of the Arabidopsis thaliana aae3 (Ataae3) seed mucilage phenotype. Ruthidium red (RR) staining of Ataae3 and wild type (WT) seeds suggested that the observed reduction in Ataae3 germination may be attributable, at least in part, to a decrease in seed mucilage accumulation. Quantitative RT-PCR analysis revealed that the expression of selected mucilage regulatory transcription factors, as well as of biosynthetic and extrusion genes, was significantly down-regulated in the Ataae3 seeds. Mucilage accumulation in seeds from an engineered oxalate-accumulating Arabidopsis and Atoxc mutant, blocked in the second step of the CoA-dependent pathway of oxalate catabolism, were found to be similar to WT. These findings suggest that elevated tissue oxalate concentrations and loss of the oxalate catabolism pathway downstream of AAE3 were not responsible for the reduced Ataae3 seed germination and mucilage phenotypes. Overall, our findings unveil the presence of regulatory interplay between AAE3 and transcriptional control of mucilage gene expression.

Investigations on Microbes Attached to the Cuticle of Phytonematodes

Nematodes form various associations with soil microbiome. Experimental studies on nematode-attached microbes can improve mechanistic understanding of these associations and lead to new discoveries relevant for the field of nematode biocontrol. Microbial attachment to the surface of phytonematodes is very specific and influenced by a multitude of factors, including the designation of nematodes and microbes, environmental and biological factors in soil, time of incubation, and the ratio and evolutionary trajectories between nematodes and microbes. Here, we describe how the classical nematological and microbiological techniques can be coupled with the advanced molecular tools to study the microbial attachment to phytonematodes in soil. We focus on the characterization of nematode-attached microbes using classical microbiological approaches and high-throughput amplicon sequencing and on the effects of nematode-attached microbes on plant defense responses.

Exploring the diverse applications of Carbohydrate macromolecules in food, pharmaceutical, and environmental technologies

Carbohydrates are a class of macromolecules that has significant potential across several domains, including the organisation of genetic material, provision of structural support, and facilitation of defence mechanisms against invasion. Their molecular diversity enables a vast array of essential functions, such as energy storage, immunological signalling, and the modification of food texture and consistency. Due to their rheological characteristics, solubility, sweetness, hygroscopicity, ability to prevent crystallization, flavour encapsulation, and coating capabilities, carbohydrates are useful in food products. Carbohydrates hold potential for the future of therapeutic development due to their important role in sustained drug release, drug targeting, immune antigens, and adjuvants. Bio-based packaging provides an emerging phase of materials that offer biodegradability and biocompatibility, serving as a substitute for traditional non-biodegradable polymers used as coatings on paper. Blending polyhydroxyalkanoates (PHA) with carbohydrate biopolymers, such as starch, cellulose, polylactic acid, etc., reduces the undesirable qualities of PHA, such as crystallinity and brittleness, and enhances the PHA's properties in addition to minimizing manufacturing costs. Carbohydrate-based biopolymeric nanoparticles are a viable and cost-effective way to boost agricultural yields, which is crucial for the increasing global population. The use of biopolymeric nanoparticles derived from carbohydrates is a potential and economically viable approach to enhance the quality and quantity of agricultural harvests, which is of utmost importance given the developing global population. The carbohydrate biopolymers may play in plant protection against pathogenic fungi by inhibiting spore germination and mycelial growth, may act as effective elicitors inducing the plant immune system to cope with pathogens. Furthermore, they can be utilised as carriers in controlled-release formulations of agrochemicals or other active ingredients, offering an alternative approach to conventional fungicides. It is expected that this review provides an extensive summary of the application of carbohydrates in the realms of food, pharmaceuticals, and environment.

Involvement of cyclic nucleotide-gated channels in soybean cyst nematode chemotaxis and thermotaxis

The soybean cyst nematode (SCN) is one of the most damaging pests affecting soybean production. SCN displays important host recognition behaviors, such as hatching and infection, by recognizing several compounds produced by the host. Therefore, controlling SCN behaviors such as chemotaxis and thermotaxis is an attractive pest control strategy. In this study, we found that cyclic nucleotide-gated channels (CNG channels) regulate SCN chemotaxis and thermotaxis and Hg-tax-2, a gene encoding a CNG channel, is an important regulator of SCN behavior. Gene silencing of Hg-tax-2 and treatment with a CNG channel inhibitor reduced the attraction of second-stage juveniles to nitrate, an attractant with a different recognition mechanism from the host-derived chemoattractant(s), and to host soybean roots, as well as their avoidance behavior toward high temperatures. Co-treatment of ds Hg-tax-2 with the CNG channel inhibitor indicated that Hg-tax-2 is a major regulator of SCN chemotaxis and thermotaxis. These results suggest new avenues for research on control of SCN.

Attraction of second-stage juveniles of Meloidogyne species to fluopyram

BACKGROUND

Several benzenoid aromatic compounds were found to attract second-stage juveniles (J2) of Meloidogyne species in previous studies. Here, the attraction of Meloidogyne J2 to the nematicides fluopyram and fluensulfone, with and without aromatic attractants, was evaluated on agar plates and in sand.

RESULTS

Fluensulfone mixed with 2-methoxybenzaldehyde, carvacrol, trans-cinnamic acid, and 2-methoxycinnamaldehyde, attracted Meloidogyne javanica J2 on an agar plate, whereas fluensulfone alone did not. In contrast, fluopyram alone attracted J2 of M. javanica, Meloidogyne hapla, and Meloidogyne marylandi, although higher numbers of M. javanica J2 were attracted to the nematicide with the aromatic compounds. Trap tubes loaded with 1 and 2 μg fluopyram attracted M. javanica, Meloidogyne incognita, M. hapla, and M. marylandi J2 in the sand. Fluopyram-treated tubes attracted 4.4-6.3 times higher numbers of M. javanica and M. marylandi J2 than fluensulfone. Potassium nitrate (KNO₃ ), a Meloidogyne J2 repellent, did not abolish fluopyram's attractiveness to M. marylandi. These results indicate that high numbers of Meloidogyne J2 near fluopyram on an agar plate or in sand are caused by the attractiveness of the nematicide and not by the accumulation of dead J2 after their random encounter with the nematicide.

CONCLUSION

Aromatic attractants have the potential to attract Meloidogyne J2 to nematicides; however, fluopyram itself was attractive to Meloidogyne J2. The attractiveness of fluopyram to Meloidogyne J2 might contribute to its high control efficacy, and elucidation of the attraction mechanism could be useful for nematode-control strategies. © 2023 Society of Chemical Industry.

It's time to go glyco in cell wall bioengineering

Tailoring the structure of cellulose, hemicellulose or pectin in plant cell walls can modulate growth, disease resistance, biomass yield and other important agronomic traits. Recent advances in the biosynthesis of microfibrils and matrix polysaccharides force us to re-examine old assumptions about the assembly and functions of cell wall components. The engineering of living or hybrid materials in microorganisms could be adapted to plant biopolymers or to inspire the development of new plant-based composites. High-throughput cellular factories and synthetic biology toolkits could unveil the biological roles and biotechnological potential of the large, unexplored space of carbohydrate-active enzymes. Increasing automation and enhanced carbohydrate detection methods are unlocking new routes to design plant glycans for a sustainable bioeconomy.

Rhamnogalacturonan-I as a nematode chemoattractant from Lotus corniculatus L. super-growing root culture

INTRODUCTION

The soil houses a tremendous amount of micro-organisms, many of which are plant parasites and pathogens by feeding off plant roots for sustenance. Such root pathogens and parasites often rely on plant-secreted signaling molecules in the rhizosphere as host guidance cues. Here we describe the isolation and characterization of a chemoattractant of plant-parasitic root-knot nematodes (Meloidogyne incognita, RKN).

METHODS

The Super-growing Root (SR) culture, consisting of excised roots from the legume species Lotus corniculatus L., was found to strongly attract infective RKN juveniles and actively secrete chemoattractants into the liquid culture media. The chemo-attractant in the culture media supernatant was purified using hydrophobicity and anion exchange chromatography, and found to be enriched in carbohydrates.

RESULTS

Monosaccharide analyses suggest the chemo-attractant contains a wide array of sugars, but is enriched in arabinose, galactose and galacturonic acid. This purified chemoattractant was shown to contain pectin, specifically anti-rhamnogalacturonan-I and anti-arabinogalactan protein epitopes but not anti-homogalacturonan epitopes. More importantly, the arabinose and galactose sidechain groups were found to be essential for RKN-attracting activities. This chemo-attractant appears to be specific to M. incognita, as it wasn't effective in attracting other Meloidogyne species nor Caenorhabditis elegans.

DISCUSSION

This is the first report to identify the nematode attractant purified from root exudate of L corniculatus L. Our findings re-enforce pectic carbohydrates as important chemicals mediating micro-organism chemotaxis in the soil, and also highlight the unexpected utilities of the SR culture system in root pathogen research.

Recognition and Response in Plant-Nematode Interactions

Plant-parasitic nematodes spend much of their lives inside or in contact with host tissue, and molecular interactions constantly occur and shape the outcome of parasitism. Eggs of these parasites generally hatch in the soil, and the juveniles must locate and infect an appropriate host before their stored energy is exhausted. Components of host exudate are evaluated by the nematode and direct its migration to its infection site. Host plants recognize approaching nematodes before physical contact through molecules released by the nematodes and launch a defense response. In turn, nematodes deploy numerous mechanisms to counteract plant defenses. This review focuses on these early stages of the interaction between plants and nematodes. We discuss how nematodes perceive and find suitable hosts, how plants perceive and mount a defense response against the approaching parasites, and how nematodes fight back against host defenses.

Toward Chemical Ecology of Plant-Parasitic Nematodes: Kairomones, Pheromones, and Other Behaviorally Active Chemical Compounds

An overview of natural chemical compounds involved in plant-parasitic nematode (PPN) behavior is presented and classified following a system accepted by chemoecologists. Kairomonal and other egg-hatching stimulants, as well as attractants for juveniles, are presented. Sex, aggregation, egg-hatching, and putative diapause PPN pheromones are analyzed and grouped into clusters of primers and releasers. The role of over 500 chemical compounds, both organic and inorganic, involved in PPN behavior is reviewed, with the most widely analyzed and least studied fields of PPN chemical ecology indicated. Knowledge on PPN chemical ecology facilitates environmentally friendly integrated pest management. This could be achieved by disrupting biointeractions between nematodes and their host plants and/or between nematodes. Data on biologically active chemicals reveals targets for resistant plant selection, including through application of gene silencing techniques.

The Role of Fucose-Containing Glycan Motifs Across Taxonomic Kingdoms

The extraordinary diversity of glycans leads to large differences in the glycomes of different kingdoms of life. Yet, while most monosaccharides are solely found in certain taxonomic groups, there is a small set of monosaccharides with widespread distribution across nearly all domains of life. These general monosaccharides are particularly relevant for glycan motifs, as they can readily be used by commensals and pathogens to mimic host glycans or hijack existing glycan recognition systems. Among these, the monosaccharide fucose is especially interesting, as it frequently presents itself as a terminal monosaccharide, primed for interaction with proteins. Here, we analyze fucose-containing glycan motifs across all taxonomic kingdoms. Using a hereby presented large species-specific glycan dataset and a plethora of methods for glycan-focused bioinformatics and machine learning, we identify characteristic as well as shared fucose-containing glycan motifs for various taxonomic groups, demonstrating clear differences in fucose usage. Even within domains, fucose is used differentially based on an organism’s physiology and habitat. We particularly highlight differences in fucose-containing motifs between vertebrates and invertebrates. With the example of pathogenic and non-pathogenic Escherichia coli strains, we also demonstrate the importance of fucose-containing motifs in molecular mimicry and thereby pathogenic potential. We envision that this study will shed light on an important class of glycan motifs, with potential new insights into the role of fucosylated glycans in symbiosis, pathogenicity, and immunity.