Induction of auxin biosynthesis and WOX5 repression mediate changes in root development in Arabidopsis exposed to chitosan

The Evolution of the WUSCHEL-Related Homeobox Gene Family in Dendrobium Species and Its Role in Sex Organ Development in D. chrysotoxum

The WUSCHEL-related homeobox (WOX) transcription factor plays a vital role in stem cell maintenance and organ morphogenesis, which are essential processes for plant growth and development. Dendrobium chrysotoxum, D. huoshanense, and D. nobile are valued for their ornamental and medicinal properties. However, the specific functions of the WOX gene family in Dendrobium species are not well understood. In our study, a total of 30 WOX genes were present in the genomes of the three Dendrobium species (nine DchWOXs, 11 DhuWOXs, and ten DnoWOXs). These 30 WOXs were clustered into ancient clades, intermediate clades, and WUS/modern clades. All 30 WOXs contained a conserved homeodomain, and the conserved motifs and gene structures were similar among WOXs belonging to the same branch. D. chrysotoxum and D. huoshanense had one pair of fragment duplication genes and one pair of tandem duplication genes, respectively; D. nobile had two pairs of fragment duplication genes. The cis-acting regulatory elements (CREs) in the WOX promoter region were mainly enriched in the light response, stress response, and plant growth and development regulation. The expression pattern and RT-qPCR analysis revealed that the WOXs were involved in regulating the floral organ development of D. chrysotoxum. Among them, the high expression of DchWOX3 suggests that it might be involved in controlling lip development, whereas DchWOX5 might be involved in controlling ovary development. In conclusion, this work lays the groundwork for an in-depth investigation into the functions of WOX genes and their regulatory role in Dendrobium species' floral organ development.

Plant-endophyte communication: Scaling from molecular mechanisms to ecological outcomes

Diverse communities of fungal endophytes reside in plant tissues, where they affect and are affected by plant physiology and ecology. For these intimate interactions to form and persist, endophytes and their host plants engage in intricate systems of communication. The conversation between fungal endophytes and plant hosts ultimately dictates endophyte community composition and function and has cascading effects on plant health and plant interactions. In this review, we synthesize our current knowledge on the mechanisms and strategies of communication used by endophytic fungi and their plant hosts. We discuss the molecular mechanisms of communication that lead to organ specificity of endophytic communities and distinguish endophytes, pathogens, and saprotrophs. We conclude by offering emerging perspectives on the relevance of plant-endophyte communication to microbial community ecology and plant health and function.

NnWOX1-1, NnWOX4-3, and NnWOX5-1 of lotus (Nelumbo nucifera Gaertn)promote root formation and enhance stress tolerance in transgenic Arabidopsis thaliana

BACKGROUND

Adventitious roots (ARs) represent an important organ system for water and nutrient uptake in lotus plants because of degeneration of the principal root. The WUSCHEL-related homeobox (WOX) gene regulates plant development and growth by affecting the expression of several other genes. In this study, three WOX genes, NnWOX1-1, NnWOX4-3, and NnWOX5-1, were isolated and their functions were assessed in Arabidopsis plants.

RESULTS

The full lengths of NnWOX1-1, NnWOX4-3, and NnWOX5-1 were 1038, 645, and 558 bp, encoding 362, 214, and 185 amino acid residues, respectively. Phylogenetic analysis classified NnWOX1-1 and NnWOX4-3 encoding proteins into one group, and NnWOX5-1 and MnWOX5 encoding proteins exhibited strong genetic relationships. The three genes were induced by sucrose and indoleacetic acid (IAA) and exhibited organ-specific expression characteristics. In addition to improving root growth and salt tolerance, NnWOX1-1 and NnWOX4-3 promoted stem development in transgenic Arabidopsis plants. A total of 751, 594, and 541 genes, including 19, 19, and 13 respective genes related to ethylene and IAA metabolism and responses, were enhanced in NnWOX1-1, NnWOX4-3, and NnWOX5-1 transgenic plants, respectively. Further analysis showed that ethylene production rates in transgenic plants increased, whereas IAA, peroxidase, and lignin content did not significantly change. Exogenous application of ethephon on lotus seedlings promoted AR formation and dramatically increased the fresh and dry weights of the plants.

CONCLUSIONS

NnWOX1-1, NnWOX4-3, and NnWOX5-1 influence root formation, stem development, and stress adaptation in transgenic Arabidopsis plants by affecting the transcription of multiple genes. Among these, changes in gene expression involving ethylene metabolism and responses likely critically affect the development of Arabidopsis plants. In addition, ethylene may represent an important factor affecting AR formation in lotus seedlings.

Chitosan from Marine Amphipods Inhibits the Wilt Banana Pathogen Fusarium oxysporum f. sp. Cubense Tropical Race 4

In this work, we extracted chitosan from marine amphipods associated with aquaculture facilities and tested its use in crop protection. The obtained chitosan was 2.5 ± 0.3% of initial ground amphipod dry weight. The chemical nature of chitosan from amphipod extracts was confirmed via Raman scattering spectroscopy and Fourier transform infrared spectroscopy (FTIR). This chitosan showed an 85.7-84.3% deacetylation degree. Chitosan from biofouling amphipods at 1 mg·mL-1 virtually arrested conidia germination (ca. sixfold reduction from controls) of the banana wilt pathogenic fungus Fusarium oxysporum f. sp cubense Tropical Race 4 (FocTR4). This concentration reduced (ca. twofold) the conidia germination of the biocontrol fungus Pochonia chlamydosporia (Pc123). Chitosan from amphipods at low concentrations (0.01 mg·mL-1) still reduced FocTR4 germination but did not affect Pc123. This is the first time that chitosan is obtained from biofouling amphipods. This new chitosan valorizes aquaculture residues and has potential for biomanaging the diseases of food security crops such as bananas.

Hormonal and proteomic analyses of southern blight disease caused by Athelia rolfsii and root chitosan priming on Cannabis sativa in an in vitro hydroponic system

Southern blight disease, caused by the fungal pathogen Athelia rolfsii, suppresses plant growth and reduces product yield in Cannabis sativa agriculture. Mechanisms of pathology of this soil-borne disease remain poorly understood, with disease management strategies reliant upon broad-spectrum antifungal use. Exposure to chitosan, a natural elicitor, has been proposed as an alternative method to control diverse fungal diseases in an eco-friendly manner. In this study, C. sativa plants were grown in the Root-TRAPR system, a transparent hydroponic growth device, where plant roots were primed with .2% colloidal chitosan prior to A. rolfsii inoculation. Both chitosan-primed and unprimed inoculated plants displayed classical symptoms of wilting and yellowish leaves, indicating successful infection. Non-primed infected plants showed increased shoot defense responses with doubling of peroxidase and chitinase activities. The levels of growth and defense hormones including auxin, cytokinin, and jasmonic acid were increased 2-5-fold. In chitosan-primed infected plants, shoot peroxidase activity and phytohormone levels were decreased 1.5-4-fold relative to the unprimed infected plants. When compared with shoots, roots were less impacted by A. rolfsii infection, but the pathogen secreted cell wall-degrading enzymes into the root-growth solution. Chitosan priming inhibited root growth, with root lengths of chitosan-primed plants approximately 65% shorter than the control, but activated root defense responses, with root peroxidase activity increased 2.7-fold along with increased secretion of defense proteins. The results suggest that chitosan could be an alternative platform to manage southern blight disease in C. sativa cultivation; however, further optimization is required to maximize effectiveness of chitosan.

Chitosan-induced biotic stress tolerance and crosstalk with phytohormones, antioxidants, and other signalling molecules

Several polysaccharides augment plant growth and productivity and galvanise defence against pathogens. Such elicitors have ecological superiority over traditional growth regulators, considering their amplified biocompatibility, biodegradability, bioactivity, non-toxicity, ubiquity, and inexpensiveness. Chitosan is a chitin-derived polysaccharide that has recently been spotlighted among plant scientists. Chitosan supports plant growth and development and protects against microbial entities such as fungi, bacteria, viruses, nematodes, and insects. In this review, we discuss the current knowledge of chitosan's antimicrobial and insecticidal potential with recent updates. These effects are further explored with the possibilities of chitosan's active correspondence with phytohormones such as jasmonic acid (JA), salicylic acid (SA), indole acetic acid (IAA), abscisic acid (ABA), and gibberellic acid (GA). The stress-induced redox shift in cellular organelles could be substantiated by the intricate participation of chitosan with reactive oxygen species (ROS) and antioxidant metabolism, including hydrogen peroxide (H2O2), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Furthermore, we propose how chitosan could be intertwined with cellular signalling through Ca2+, ROS, nitric oxide (NO), transcription factors (TFs), and defensive gene activation.

Effects of chitin and chitosan on root growth, biochemical defense response and exudate proteome of Cannabis sativa

Fungal pathogens pose a major threat to Cannabis sativa production, requiring safe and effective management procedures to control disease. Chitin and chitosan are natural molecules that elicit plant defense responses. Investigation of their effects on C. sativa will advance understanding of plant responses towards elicitors and provide a potential pathway to enhance plant resistance against diseases. Plants were grown in the in vitro Root-TRAPR system and treated with colloidal chitin and chitosan. Plant morphology was monitored, then plant tissues and exudates were collected for enzymatic activity assays, phytohormone quantification, qPCR analysis and proteomics profiling. Chitosan treatments showed increased total chitinase activity and expression of pathogenesis-related (PR) genes by 3-5 times in the root tissues. In the exudates, total peroxidase and chitinase activities and levels of defense proteins such as PR protein 1 and endochitinase 2 were increased. Shoot development was unaffected, but root development was inhibited after chitosan exposure. In contrast, chitin treatments had no significant impact on any defense parameters, including enzymatic activities, hormone quantities, gene expression levels and root secreted proteins. These results indicate that colloidal chitosan, significantly enhancing defense responses in C. sativa root system, could be used as a potential elicitor, particularly in hydroponic scenarios to manage crop diseases.

Chitosan-based Schiff base-metal (Fe, Cu, and Zn) complexes mitigate the negative consequences of drought stress on pomegranate fruits

Drought is one of the major environmental stresses that impairs fruit productivity and quality. The proper management of minerals can, however, assist plant to maintain their growth even under drought incidents, and is considered one of the encouraging approaches to refine the drought tolerance of plants. The beneficial effects of chitosan (CH)-based Schiff base-metal complexes (e.g., CH-Fe, CH-Cu and CH-Zn) in reducing the harmful impacts of different levels of drought stress on the growth and productivity of 'Malase Saveh' pomegranate cultivar were examined. All CH-metal complexes displayed favorable effects on the yield- and growth-related attributes of pomegranate trees cultivated under well-watered and different drought situations, with the best effects were observed with CH-Fe application. Specifically, leaves of CH-Fe-treated pomegranate plants showed higher concentrations of photosynthetic pigments [chlorophyll a (Chl a), Chl b, Chl a+b, and carotenoids by 28.0, 29.5, 28.6 and 85.7%, respectively] and microelements (Fe by 27.3%), along with increased levels of superoxide dismutase (by 35.3%) and ascorbate peroxidase (by 56.0%) enzymatic activities relative to those of CH-Fe-non-treated pomegranate plants under intense drought stress. CH-Fe-treated drought-stressed pomegranate leaves showed high increment of abscisic acid (by 25.1%) and indole-3-acetic acid (by 40.5%) relative to CH-Fe-non-treated pomegranates. The increased contents of total phenolics, ascorbic acid, total anthocyanins, and titratable acidity (by 24.3, 25.8, 9.3 and 30.9%, respectively) in the fruits of CH-Fe-treated drought-stressed pomegranates indicated the advantageousness of CH-Fe on the enhancement of fruit nutritional qualities. Collectively, our results prove the explicit functions of these complexes, particularly CH-Fe, in the control of drought-induced negative effects on pomegranate trees grown in semi-arid and dry areas.

Chitosan nanoparticles support the impact of arbuscular mycorrhizae fungi on growth and sugar metabolism of wheat crop

Arbuscular mycorrhizae fungi (AMF) symbiosis is an indispensable approach in sustainable agriculture. AMF-plant association is likely to be enhanced by the nanoparticle's application. Herein, the impact of chitosan nanoparticles (CSNPs) on the mycorrhizal colonization in wheat has been investigated. The provoked changes in wheat growth, physiology and metabolism were assessed. CSNPs treatment improved AMF colonization (52 %) by inducing the levels of auxins and strigolactones in roots by 32 and 21 %, respectively besides flavonoids exudation into the rhizosphere (9 %). Such supporting action of CSNPs was associated with improved plant biomass production (21 %) compared to AMF treatment. Both treatments synergistically enhanced the photochemical efficiency of photosystem II and stomatal conductance, therefore the photosynthetic rate was increased. The combined application of CSNPs and AMF enhanced accumulation of glucose, fructose, sucrose, and starch (12, 22, 31 and 13 %, respectively), as well as the activities of sucrose-p-synthase, invertases and starch synthase compared to AMF treatment. The synchronous application of CSNPs and AMF promoted the levels of polyphenols, carotenoids, and tocopherols therefore, improved antioxidant capacity (33 %), in the roots. CSNPs can be applied as an efficient biofertilization strategies to enhance plant growth and fitness, beside improvement of health promoting compounds in wheat.

Effect of Seed Priming with Chitosan Hydrolysate on Lettuce (Lactuca sativa) Growth Parameters

Seed priming increases germination, yield, and resistance to abiotic factors and phytopathogens. Chitosan is considered an ecofriendly growth stimulant and crop protection agent. Chitosan hydrolysate (CH) is an unfractionated product of hydrolysis of high-molecular-weight crab shell chitosan with a molecular weight of 1040 kDa and a degree of deacetylation of 85% with nitric acid. The average molecular weight of the main fraction in CH was 39 kDa. Lettuce seeds were soaked in 0.01-1 mg/mL CH for 6 h before sowing. The effects of CH on seed germination, plant morphology, and biochemical indicators at different growth stages were evaluated. Under the 0.1 mg/mL CH treatment, earlier seed germination was detected compared to the control. Increased root branching was observed, along with 100% and 67% increases in fresh weight (FW) at the 24th and 38th days after sowing (DAS), respectively. An increase in the shoot FW was found in CH-treated plants (33% and 4% at the 24th and 38th DAS, respectively). Significant increases in chlorophyll and carotenoid content compared to the control were observed at the 10th DAS. There were no significant differences in the activity of phenylalanine ammonia-lyase, polyphenol oxidase, β-1,3-glucanase, and chitinase at the 24th and 38th DAS. Seed priming with CH could increase the yield and uniformity of plants within the group. This effect is important for commercial vegetable production.

Bioformulations Derived from Enterobacter sp. NRRU-N13 and Oligochitosan Alleviate Drought Stress in Thai Jasmine Rice (Oryza sativa L. var. KDML105)

Climate change is predicted to increase the length, severity, and frequency of drought, which limits plant development by changing various physiological and biochemical processes. Therefore, the present study investigated the effects of drought stress on indole-3-acetic and exopolysaccharide production by Enterobacter sp. NRRU-N13, developed bioformulations of plant growth-promoting Enterobacter sp. NRRU-N13, and evaluated the synergistic effects of these bioformulations in combination with different chitosans on the physiological responses of rice under drought stress. Drought stress inhibited the biosynthesis of indole-3-acetic and exopolysaccharides by Enterobacter sp. NRRU-N13. The viability and stability of Enterobacter sp. NRRU-N13 in bioformulations ranged between 4.70 and 5.70 log CFU g-1 after 80 days at an ambient temperature. Oligochitosan and chitosan at 40‍ ‍mg L-1 were appropriate concentrations for improving rice seedling growth, namely, plant height, root length, shoot and root fresh weights, biomass, and the vigor index (P<0.05). The abilities of these bioformulations, in combination with oligochitosan and chitosan, to alleviate drought stress in rice were examined. The results obtained revealed that the combined application of oligochitosan (40‍ ‍mg L-1) and the FON13 bioformulation (filter cake+40‍ ‍mg kg-1 oligochitosan+10% Enterobacter sp. NRRU-N13) exerted the strongest synergistic effects to alleviate drought stress in rice plants by increasing ascorbate peroxidase and catalase activities, chlo-rophyll concentrations, and relative water content and suppressing proline accumulation and electrolyte leakage from rice plants under drought stress. The present results indicate that the application of oligochitosan combined with these bioformulations effectively improved plant physiology and development. Therefore, the combined application of oligochitosan and a bioformulation of Enterobacter sp. NRRU-N13 is recommended to alleviate drought stress in rice plants.

In vitro propagation and assessment of genetic stability in date palm as affected by chitosan and thidiazuron combinations

BACKGROUND

Mass propagation of date palm has attracted the interest of commercial producers. However, this technique still faces many obstacles that hinder production. This study investigated the effect of chitosan (CHT) at various concentrations for the possibility to apply it in combination with thidiazuron (TDZ) on the growth and development of tissue cultures of Barhee cultivar.

RESULTS

The results showed that CHT and TDZ on in vitro proliferation of Barhee date palm cultivar were significant. The highest response rate and the number of shoots per jar were found in MS media supplemented with 15 mgL^-1 CHT and 0.5 mgL^-1 TDZ combination. Furthermore, we found that the combined application between 20 mg L^-1 CHT+ 1.0 mg L^-1 TDZ resulted in the highest shoots content of endogenous IAA, compared with other treatments. At the same time, the data revealed that the maximum cytokinins (CKs) content of shoots occurred in a medium supplemented with 15 mg L^-1 CHT and 0.5 mg L^-1 TDZ. The genetic stability of the discussed micropropagation protocol was confirmed in this study by DNA-based technique RAPD (random amplified polymorphic DNA). The results may indicate that the micropropagation protocol developed in this research paper was appropriate and applicable for producing genetically stable date palm cv Barhee plants.

CONCLUSION

Applying the strategy of culture treatment with (CHT) and (TDZ) can be valuable for improving the propagation of date palm cv Barhee in vitro.

The Effect of Chitosan on Plant Physiology, Wound Response, and Fruit Quality of Tomato

In agriculture, chitosan has become popular as a metabolic enhancer; however, no deep information has been obtained yet regarding its mechanisms on vegetative tissues. This work was conducted to test the impact of chitosan applied at different plant growth stages on plant development, physiology, and response to wounding as well as fruit shape and composition. Five concentrations of chitosan were tested on tomato. The most effective chitosan doses that increased leaf number, leaf area, plant biomass, and stomatal conductance were 0.75 and 1 mg mL^-1. Chitosan (1 mg mL^-1) applied as foliar spray increased the levels of jasmonoyl-isoleucine and abscisic acid in wounded roots. The application of this dose at vegetative and flowering stages increased chlorophyll fluorescence (Fv/Fm) values, whereas application at the fruit maturation stage reduced the Fv/Fm values. This decline was positively correlated with fruit shape and negatively correlated with the pH and the content of soluble sugars, lycopene, total flavonoids, and nitrogen in fruits. Moreover, the levels of primary metabolites derived from glycolysis, such as inositol phosphate, lactic acid, and ascorbic acid, increased in response to treatment of plants with 1 mg mL^-1- chitosan. Thus, chitosan application affects various plant processes by influencing stomata aperture, cell division and expansion, fruit maturation, mineral assimilation, and defense responses.

Genome-wide identification and expression profiling of WUSCHEL-related homeobox (WOX) genes confer their roles in somatic embryogenesis, growth and abiotic stresses in banana

Plant-specific WUSCHEL-related homeobox (WOX) transcription factors are known to be involved in plant developmental processes, especially in embryogenesis. In this study, a total of thirteen WOX members were identified in the banana (Musa acuminata) genome (MaWOX) and characterized for in-silico analysis. Phylogenetic analysis revealed that these genes were divided into three clades (ancient, intermediate and modern) which reflected the evolutionary history of WOX families. Furthermore, modern clade members have shown higher variations in gene structural features and carried unique conserved motifs (motif 3 and motif 4) when compared to the members of other clades. The differential expression of all 13 MaWOX was observed in early (embryogenic cell suspension (ECS), multiplying ECS, germinating embryos, young leaflet and node of germinated plantlets) and late (unripe fruit peel and pulp, ripe fruit peel and pulp) developmental stages of banana cultivar Grand Naine. The maximum expression of MaWOX6 (18 fold) and MaWOX13 (120 fold) was found during somatic embryogenesis and in unripe fruit pulp, respectively. Moreover, numerous cis-elements responsive to drought, cold, ethylene, methyl jasmonate (MeJA), abscisic acid (ABA) and gibberellic acid (GA) were observed in all MaWOX promoter regions. The subsequent expression analysis under various abiotic stresses (cold, drought and salt) revealed maximum expression of the MaWOX3 (830 fold), MaWOX8a (30 fold) and MaWOX11b (105 fold) in salt stress. It gives evidence about their possible role in salt stress tolerance in banana. Hence, the present study provides precise information on the MaWOX gene family and their expression in various tissues and stressful environmental conditions that may help to develop climate-resilient banana plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03387-w.

Chitosan and nematophagous fungi for sustainable management of nematode pests

Plants are exposed to large number of threats caused by herbivores and pathogens which cause important losses on crops. Plant pathogens such as nematodes can cause severe damage and losses in food security crops worldwide. Chemical pesticides were extendedly used for nematode management. However, due to their adverse effects on human health and the environment, they are now facing strong limitations by regulatory organisations such as EFSA (European Food Safety Authority). Therefore, there is an urgent need for alternative and efficient control measures, such as biological control agents or bio-based plant protection compounds. In this scenario, chitosan, a non-toxic polymer obtained from seafood waste mainly, is becoming increasingly important. Chitosan is the N-deacetylated form of chitin. Chitosan is effective in the control of plant pests and diseases. It also induces plants defence mechanisms. Chitosan is also compatible with some biocontrol microorganisms mainly entomopathogenic and nematophagous fungi. Some of them are antagonists of nematode pests of plants and animals. The nematophagous biocontrol fungus Pochonia chlamydosporia has been widely studied for sustainable management of nematodes affecting economically important crops and for its capability to grow with chitosan as only nutrient source. This fungus infects nematode eggs using hyphal tips and appressoria. Pochonia chlamydosporia also colonizes plant roots endophytically, stimulating plant defences by induction of salicylic and jasmonic acid biosynthesis and favours plant growth and development. Therefore, the combined use of chitosan and nematophagous fungi could be a novel strategy for the biological control of nematodes and other root pathogens of food security crops.

Phosphoprotein Profile of Rice (Oryza sativa L.) Seedlings under Osmotic Stress after Pretreatment with Chitosan

This study aims to identify novel chitosan (CTS)-responsive phosphoproteins in Leung Pratew 123 (LPT123) and Khao Dawk Mali 105 (KDML105) as drought-sensitive rice cultivars and differences in the CTS response. Rice seeds were soaked in CTS solution before germination, and 2- and 4-week-old rice seedlings sprayed with CTS before osmotic stress comprised the following four groups: (1) seedlings treated with distilled water; (2) seedlings treated with CTS; (3) seedlings pretreated with distilled water and subjected to osmotic stress; and (4) seedlings pretreated with CTS and subjected to osmotic stress. Phosphoproteins of leaf tissues were enriched using immobilized metal affinity chromatography (IMAC) before tryptic digestion and analysis via LC-MS. Phosphoprotein profiling analyses led to the identification of 4721 phosphoproteins representing 1052 and 1040 unique phosphoproteins in the LPT123 and KDML105 seedlings, respectively. In response to CTS pretreatment before osmotic stress, 22 differently expressed proteins were discovered, of which 10 and 12 were identified in the LPT123 and KDML105, respectively. These proteins are typically involved in signaling, transport, protein folding, protein degradation, and metabolism. This study provides fruitful data to understand the signal transduction mechanisms of rice seedlings pretreated with CTS before exposure to osmotic stress.

Root-TRAPR: a modular plant growth device to visualize root development and monitor growth parameters, as applied to an elicitor response of Cannabis sativa

BACKGROUND

Plant growth devices, for example, rhizoponics, rhizoboxes, and ecosystem fabrication (EcoFAB), have been developed to facilitate studies of plant root morphology and plant-microbe interactions in controlled laboratory settings. However, several of these designs are suitable only for studying small model plants such as Arabidopsis thaliana and Brachypodium distachyon and therefore require modification to be extended to larger plant species like crop plants. In addition, specific tools and technical skills needed for fabricating these devices may not be available to researchers. Hence, this study aimed to establish an alternative protocol to generate a larger, modular and reusable plant growth device based on different available resources.

RESULTS

Root-TRAPR (Root-Transparent, Reusable, Affordable three-dimensional Printed Rhizo-hydroponic) system was successfully developed. It consists of two main parts, an internal root growth chamber and an external structural frame. The internal root growth chamber comprises a polydimethylsiloxane (PDMS) gasket, microscope slide and acrylic sheet, while the external frame is printed from a three-dimensional (3D) printer and secured with nylon screws. To test the efficiency and applicability of the system, industrial hemp (Cannabis sativa) was grown with or without exposure to chitosan, a well-known plant elicitor used for stimulating plant defense. Plant root morphology was detected in the system, and plant tissues were easily collected and processed to examine plant biological responses. Upon chitosan treatment, chitinase and peroxidase activities increased in root tissues (1.7- and 2.3-fold, respectively) and exudates (7.2- and 21.6-fold, respectively). In addition, root to shoot ratio of phytohormone contents were increased in response to chitosan. Within 2 weeks of observation, hemp plants exhibited dwarf growth in the Root-TRAPR system, easing plant handling and allowing increased replication under limited growing space.

CONCLUSION

The Root-TRAPR system facilitates the exploration of root morphology and root exudate of C. sativa under controlled conditions and at a smaller scale. The device is easy to fabricate and applicable for investigating plant responses toward elicitor challenge. In addition, this fabrication protocol is adaptable to study other plants and can be applied to investigate plant physiology in different biological contexts, such as plant responses against biotic and abiotic stresses.

Secondary Metabolism Rearrangements in Linum usitatissimum L. after Biostimulation of Roots with COS Oligosaccharides from Fungal Cell Wall

In vitro culture of flax (Linum usitatissimum L.) was exposed to chitosan oligosaccharides (COS) in order to investigate the effects on the growth and secondary metabolites content in roots and shoots. COS are fragments of chitosan released from the fungal cell wall during plant–pathogen interactions. They can be perceived by the plant as pathogen-associated signals, mediating local and systemic innate immune responses. In the present study, we report a novel COS oligosaccharide fraction with a degree of polymerization (DP) range of 2–10, which was produced from fungal chitosan by a thermal degradation method and purified by an alcohol-precipitation process. COS was dissolved in hydroponic medium at two different concentrations (250 and 500 mg/L) and applied to the roots of growing flax seedlings. Our observations indicated that the growth of roots and shoots decreased markedly in COS-treated flax seedlings compared to the control. In addition, the results of a metabolomics analysis showed that COS treatment induced the accumulation of (neo)lignans locally at roots, flavones luteolin C-glycosides, and chlorogenic acid in systemic responses in the shoots of flax seedlings. These phenolic compounds have been previously reported to exhibit a strong antioxidant and antimicrobial activities. COS oligosaccharides, under the conditions applied in this study (high dose treatment with a much longer exposure time), can be used to indirectly trigger metabolic response modifications in planta, especially secondary metabolism, because during fungal pathogen attack, COS oligosaccharides are among the signals exchanged between the pathogen and host plant.

Biostimulants decreased nitrogen leaching and NH3 volatilization but increased N2O emission from plastic-shed greenhouse vegetable soil

Biostimulant application is an effective strategy to enhance soil fertility and plant growth. However, its comprehensive impacts on nitrogen (N) uptake and reactive N (Nr) losses via leaching, ammonia (NH₃) volatilization, and nitrous oxide (N₂O) emission from plastic-shed greenhouse vegetable system are still little known. Therefore, a field experiment was conducted with cauliflower-tomato growth rotation (from September 6, 2018, to July 17, 2019) receiving three biostimulants, i.e., humic acid (HA), algae extract (AE), and chitosan (CT), as well as a control without stimulant. The cumulative Nr losses over the cauliflower-tomato growth cycle via leaching, NH₃ volatilization, and N₂O emission were 104-175 kg N ha^-1, 2.32-3.85 kg N ha^-1, and 0.70-0.85 kg N ha^-1, respectively. Biostimulant application significantly (P < 0.05) retarded the total N leaching by 17-44% in tomato season, while suppressed the NH₃ volatilization by 18-38% in cauliflower season. Overall, AE showed the best inhibition efficiency on Nr losses by significantly (P < 0.05) decreasing total N leaching and NH₃ volatilization by 36-44% and 38-52% in both vegetable seasons, compare to the control. However, all three biostimulants stimulated the N₂O emission under both vegetable cycles. Interestingly, all biostimulant-added treatments promote the cauliflower and tomato yield, particularly following the HA and AE amendments, which bring local farmers approximately 4,384-10,035 yuan RMB ha^-1 more income. Enhanced yield under biostimulant treatments was due to higher N uptake capacity and enhanced root morphology. In summary, biostimulants have a contrasting influence on three major Nr lost pathways in greenhouse vegetable production. We recommend that AE is the most optimal biostimulant as it increases vegetable yield and decreases total N leaching and NH₃ volatilization while not dramatically increase the N₂O emission.

HACC-Based Nanoscale Delivery of the NbMLP28 Plasmid as a Crop Protection Strategy for Viral Diseases

Resistant genes as an effective strategy to antivirus of plants are at the core of sustainability efforts. We use the antiviral protein major latex protein 28 (NbMLP28 plasmid) and N-2-hydroxypropyl trimethyl ammonium chloride chitosan (HACC) designated as the HACC/NbMLP28 complex as protective gene delivery vectors to prepare nanonucleic acid drugs. The maximum drug loading capacity of HACC was 4. The particle size of HACC/NbMLP28 was measured by transmission electron microscopy and found to be approximately 40-120 nm, the particle dispersion index (PDI) was 0.448, and the ζ-potential was 22.3 mV. This facilitates its ability to deliver particles. Different controls of laser scanning confocal experiments verified the effective expression of NbMLP28 and the feasibility of nanodelivery. The optimal ratio of HACC/plasmid was 2:1. Finally, the nanoparticle/plasmid complex was tested for its ability to control diseases and was found to significantly improve resistance to three viruses. The enhanced resistance was particularly notable 4 days after inoculation. Taken together, these results indicate that HACC/NbMLP28 is a promising tool to treat plant viruses. To the best of our knowledge, this is the first study that successfully delivered and expressed antiviral protein particles in plants. This gene delivery system can effectively load antiviral plasmids and express them in plant leaves, significantly affecting the plant resistance of three RNA viruses.

Foliage application of chitosan alleviates the adverse effects of cadmium stress in wheat seedlings (Triticum aestivum L.)

Excessive cadmium (Cd) causes toxic effects on crops. The effects of chitosan (CTS) with different molecular weight (MW) (5 kDa, 3 kDa, and 1 kDa) on the growth and biochemical parameters, as well as Cd concentrations in Cd-treated wheat plants were examined in a pot experiment. The results demonstrated that foliar spraying with CTS significantly improve the wheat growth, reduce malondialdehyde content and reactive oxygen species accumulation in leaves and decrease Cd concentrations in roots and shoots of wheat seedling under Cd stress. The alleviation of Cd toxicity by CTS is probably related with the activity of antioxidant enzymes, osmotic adjustment matter and root morphology. The application of CTS enhanced the activities of superoxide dismutase, peroxidase, and catalase in Cd-stressed wheat seedling leaves by 6.6%-13.1%, 17.2%-33.0%, and 19.6%-25.5%, respectively. Besides, exogenously applied CTS also increased the soluble protein and soluble sugar contents by 17.6%-33.8% and 30.1%-36.1% in the leaves of wheat under Cd stress. Furthermore, CTS with a molecular weight of 1 kDa was the most effective in mitigating Cd toxicity in wheat seedlings, which indicates that the activity of CTS is dependent on its molecular weight. It can be concluded that the use of foliar spraying, especially with 1 kDa CTS, could have potential in reducing the damage of Cd stress.

Chitosan inhibits septin-mediated plant infection by the rice blast fungus Magnaporthe oryzae in a protein kinase C and Nox1 NADPH oxidase-dependent manner

Chitosan is a partially deacetylated linear polysaccharide composed of β-1,4-linked units of d-glucosamine and N-acetyl glucosamine. As well as a structural component of fungal cell walls, chitosan is a potent antifungal agent. However, the mode of action of chitosan is poorly understood. Here, we report that chitosan is effective for control of rice blast disease. Chitosan application impairs growth of the blast fungus Magnaporthe oryzae and has a pronounced effect on appressorium-mediated plant infection. Chitosan inhibits septin-mediated F-actin remodelling at the appressorium pore, thereby preventing repolarization of the infection cell. Chitosan causes plasma membrane permeabilization of M. oryzae and affects NADPH oxidase-dependent synthesis of reactive oxygen species, essential for septin ring formation and fungal pathogenicity. We further show that toxicity of chitosan to M. oryzae requires the protein kinase C-dependent cell wall integrity pathway, the Mps1 mitogen-activated protein kinase and the Nox1 NADPH oxidase. A conditionally lethal, analogue (PP1)-sensitive mutant of Pkc1 is partially remediated for growth in the presence of chitosan, while ∆nox1 mutants increase their glucan : chitin cell wall ratio, rendering them resistant to chitosan. Taken together, our data show that chitosan is a potent fungicide which requires the cell integrity pathway, disrupts plasma membrane function and inhibits septin-mediated plant infection.

Chitosan Plasma Chemical Processing in Beam-Plasma Reactors as a Way of Environmentally Friendly Phytostimulants Production

A novel technique of phytoactive water-soluble chitooligosaccharide (COS) production in low-temperature plasma is described. Design, operation, and control of plasma chemical reactors used to produce COS from the powder of high molecular weight chitosan are presented. The electron beam plasma is strongly non-equilibrium and chemically active; plasma was excited by injecting the scanning electron beam into reaction volume filled with aerosol, containing oxygen and chitosan powder. Plasma chemical processes, responsible for the raw chitosan destruction and techniques of these processes to obtain control of products of optimal molecular weight, are considered. COS, in amounts sufficient for laboratory tests with some plants, were produced. Tests showed that the addition of COS into the liquid growing medium at 0.25 and 1 mg/mL stimulates root growth in Arabidopsis thaliana seedlings (Col-0) by up to 40%, with respect to control plants. Foliar application of these COS formulations at 0.25 mg/mL on tomato plants (cv. Micro-Tom) also resulted in increases between 11.9% and 36% in two important plant productivity indicators (flower and fruit numbers) compared to the control plants. Being environmentally friendly (and resource saving) the electron beam plasma technology of renewable natural biopolymer processing can be considered as a competitive way to produce biostimulants for commercial agriculture.

Chitosan Induces Plant Hormones and Defenses in Tomato Root Exudates

In this work, we use electrophysiological and metabolomic tools to determine the role of chitosan as plant defense elicitor in soil for preventing or manage root pests and diseases sustainably. Root exudates include a wide variety of molecules that plants and root microbiota use to communicate in the rhizosphere. Tomato plants were treated with chitosan. Root exudates from tomato plants were analyzed at 3, 10, 20, and 30 days after planting (dap). We found, using high performance liquid chromatography (HPLC) and excitation emission matrix (EEM) fluorescence, that chitosan induces plant hormones, lipid signaling and defense compounds in tomato root exudates, including phenolics. High doses of chitosan induce membrane depolarization and affect membrane integrity. 1H-NMR showed the dynamic of exudation, detecting the largest number of signals in 20 dap root exudates. Root exudates from plants irrigated with chitosan inhibit ca. twofold growth kinetics of the tomato root parasitic fungus Fusarium oxysporum f. sp. radicis-lycopersici. and reduced ca. 1.5-fold egg hatching of the root-knot nematode Meloidogyne javanica.

A natural indole alkaloid, norharmane, affects PIN expression patterns and compromises root growth in Arabidopsis thaliana

Norharmane is an indole alkaloid that can be found in several terrestrial plants, as well as in some dinoflagellates and cyanobacteria. The aim of this study was to focus on the way this metabolite impacts the plant metabolism of the model species Arabidopsis thaliana. This metabolite caused increase of secondary and adventitious roots, as well as torsion, toxic effects, and a decrease in root length. Moreover, norharmane altered the cellular arrangement, resulting in unfinished cell walls, decreased auxin content and inhibited PIN proteins activity. All the alterations suggest that norharmane alters polar auxin transport by inhibiting PIN2, PIN3 and PIN7 transport proteins, thus causing a significant inhibitory effect on the growth of A. thaliana seedlings.

Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants

Abiotic stresses, including drought, salinity, extreme temperature, and pollutants, are the main cause of crop losses worldwide. Novel climate-adapted crops and stress tolerance-enhancing compounds are increasingly needed to counteract the negative effects of unfavorable stressful environments. A number of natural products and synthetic chemicals can protect model and crop plants against abiotic stresses through induction of molecular and physiological defense mechanisms, a process known as molecular priming. In addition to their stress-protective effect, some of these compounds can also stimulate plant growth. Here, we provide an overview of the known physiological and molecular mechanisms that induce molecular priming, together with a survey of the approaches aimed to discover and functionally study new stress-alleviating chemicals.

Chitosan microparticles improve tomato seedling biomass and modulate hormonal, redox and defense pathways

Agrobiotechnology challenges involve the generation of new sustainable bioactives with emerging properties as plant biostimulants with reduced environment impact. We analyzed the potential use of recently developed chitosan microparticles (CS-MP) as growth promoters of tomato which constitutes one of the most consumed vegetable crops worldwide. Treatments of tomato seeds with CS-MP improved germination and vigor index. In addition, CS-MP sustained application triggered an improvement in root and shoot biomass reinforcing tomato performance before transplanting. The level of reactive oxygen species (ROS), antioxidant enzyme activities and defense protein markers were modulated by CS-MP treatment in tomato plantlets. Analyses of ARR5:GUS and DR5:GUS transgenic reporter tomato lines highlighted the participation of cytokinin and auxin signaling pathways during tomato root promotion mediated by CS-MP. Our findings claim a high commercial potential of CS-MP to be incorporated as a sustainable input for tomato production.

Comprehensive analysis of WOX genes uncovers that WOX13 is involved in phytohormone-mediated fiber development in cotton

BACKGROUND

The WOX (WUSCHEL-RELATED HOMEOBOX) gene family encodes a class of transcription factors that are unique to green plants, where they are involved in regulating the development of plant tissues and organs by determining cell fate. Although the importance of the WOX gene is well known, there are few studies describing their functions in cotton.

RESULTS

In this study, 32 WOX genes were found in Gossypium hirsutum. Phylogenetic analysis showed that WOX proteins of cotton can be divided into three clades: the ancient, intermediate, and WUS clades. The number of WOX proteins in the WUS clade was greater than the sum of the proteins in the other two clades. Our analysis revealed that 20 GhWOX genes are distributed on 16 cotton chromosomes and that duplication events are likely to have contributed to the expansion of the GhWOX family. All GhWOX genes have introns, and each GhWOX protein contains multiple motifs. RNA-seq data and real-time PCR showed that GhWOX13 gene subfamily is specifically expressed at a high level in cotton fibers. We also identified putative GA, NAA, and BR response elements in the promoter regions of the GhWOX13 genes and GhWOX13 transcripts were significantly induced by GA, NAA, and BR.

CONCLUSIONS

Our data provides a useful resource for future studies on the functional roles of cotton WOX genes and shows that the GhWOX13 genes may influence cotton fiber development. Our results also provide an approach for identifying and characterizing WOX protein genes in other species.

Enhanced Properties of Chitosan Microparticles over Bulk Chitosan on the Modulation of the Auxin Signaling Pathway with Beneficial Impacts on Root Architecture in Plants

Improving the root system architecture (RSA) under adverse environmental conditions by using biostimulants is emerging as a new way to boost crop productivity. Recently, we have reported the characterization of novel chitosan-based microparticles (CS-MPs) with promising biological properties as rooting agents in lettuce. In this work, we demonstrated that in contrast to bulk chitosan (CS), which exerts root growth inhibition, CS-MPs promoted root growth and development from 1 to 10 μg mL-1 without cytotoxicity effects at higher doses in Arabidopsis and lettuce seedlings. In addition, we studied the mechanistic mode of action of CS-MPs in the development of early RSA in the Arabidopsis model. CS-MPs unchained accurate and sustained spatio-temporal activation of the nuclear auxin signaling pathway. Our findings validated a promising scenario for the application of CS-MPs in the modulation of RSA to respond to changing soil environments and improve crop performance.

The Stimulatory Effects of Nanochitin Whisker on Carbon and Nitrogen Metabolism and on the Enhancement of Grain Yield and Crude Protein of Winter Wheat

Nanochitin whisker (NC) with a cationic nature could enhance plant photosynthesis, grain yield, and quality of wheat, but have not been systematically studied. This study was designed to investigate the stimulatory effects of NC on dry matter (DM) and nitrogen (N) accumulation and translocation, and on the metabolism of carbon (C) and N in later growth stages of winter wheat to reveal the enhancement mechanism of grain yield and crude protein concentration. Different parts of NC-treated plants from pot grown experiments were collected at the pre- and post-anthesis stages. The accumulation, translocation, and contributions of DM and N from pre-anthesis vegetation organs to grains, as well as key metabolic enzyme activities, including sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC), were examined. The results showed that, at an application rate of 6 mg·kg⁻¹ of NC in the soil, the accumulation of DM and N were significantly enhanced by 16.2% and 38.8% in pre-anthesis, and by 15.4% and 30.0% in post-anthesis, respectively. Translocation of N and DM in the post-anthesis periods were enhanced by 38.4% and 50.9%, respectively. NC could also stimulate enzyme activities, and increased 39.8% and 57.1% in flag leaves, and by 36.0% and 58.8% in spikes, respectively, at anthesis. SPS and PEPC increased by 28.2% and 45.1% in flag leaves, and by 42.2% and 56.5% in spikes, respectively, at 15 days after anthesis. The results indicated that the NC promoted N metabolism more than C metabolism, and resulted in the enhancement of grain yield by 27.56% and of crude protein concentration in grain by 13.26%, respectively.

Molecular Mechanisms of Chitosan Interactions with Fungi and Plants

Chitosan is a versatile compound with multiple biotechnological applications. This polymer inhibits clinically important human fungal pathogens under the same carbon and nitrogen status as in blood. Chitosan permeabilises their high-fluidity plasma membrane and increases production of intracellular oxygen species (ROS). Conversely, chitosan is compatible with mammalian cell lines as well as with biocontrol fungi (BCF). BCF resistant to chitosan have low-fluidity membranes and high glucan/chitin ratios in their cell walls. Recent studies illustrate molecular and physiological basis of chitosan-root interactions. Chitosan induces auxin accumulation in Arabidopsis roots. This polymer causes overexpression of tryptophan-dependent auxin biosynthesis pathway. It also blocks auxin translocation in roots. Chitosan is a plant defense modulator. Endophytes and fungal pathogens evade plant immunity converting chitin into chitosan. LysM effectors shield chitin and protect fungal cell walls from plant chitinases. These enzymes together with fungal chitin deacetylases, chitosanases and effectors play determinant roles during fungal colonization of plants. This review describes chitosan mode of action (cell and gene targets) in fungi and plants. This knowledge will help to develop chitosan for agrobiotechnological and medical applications.

β-Lactam Antibiotics Modify Root Architecture and Indole Glucosinolate Metabolism in Arabidopsis thaliana

The presence of antibiotics in soils could be due to natural production by soil microorganisms or to the effect of anthropogenic activities. However, the impact of these compounds on plant physiology has not been thoroughly investigated. To evaluate the effect of β-lactam antibiotics (carbenicillin and penicillin) on the growth and development of Arabidopsis thaliana roots, plants were grown in the presence of different amounts and we found a reduction in root size, an increase in the size of root hairs as well as an abnormal position closer to the tip of the roots. Those phenomena were dependent on the accumulation of both antibiotics inside root tissues and also correlated with a decrease in size of the root apical meristem not related to an alteration in cell division but to a decrease in cell expansion. Using an RNA sequencing analysis, we detected an increase in the expression of genes related to the response to oxidative stress, which would explain the increase in the levels of endogenous reactive oxygen species found in the presence of those antibiotics. Moreover, some auxin-responsive genes were misregulated, especially an induction of CYP79B3, possibly explaining the increase in auxin levels in the presence of carbenicillin and the decrease in the amount of indole glucosinolates, involved in the control of fungal infections. Accordingly, penicillin-treated plants were hypersensitive to the endophyte fungus Colletotrichum tofieldiae. These results underscore the risks for plant growth of β-lactam antibiotics in agricultural soils, and suggest a possible function for these compounds as fungus-produced signaling molecules to modify plant behavior.

Salicylic acid loaded chitosan microparticles applied to lettuce seedlings: Recycling shrimp fishing industry waste

Shrimp fishing industry wastes are still a main problem with high environmental impact worldwide. In this study, chitosan with ultra-high molecular weight and deacetylation degree ≥85% was obtained from shrimp fishing industry waste from Argentinean Patagonia. Chitosan based microparticles capable to entrap salicylic acid, a phytohormone known to play major role in the regulation of plant defense response against various pathogens, were prepared using TPP as crosslinker. Unloaded microparticles and microparticles loading several salicylic acid amount were fully characterized exhibiting a size between 1.57 μm and 2.45 μm. Furthermore, a good PDI, entrappment efficiencies from 59% to 98% and salicylic acid sustained release over 24 h were achieved. Chitosan based microparticles were non toxic in most of the doses applied in lettuce seedlings. Instead, microparticles can positively modulate plant growth and have the potential to improve plant defense responses. In particular salicylic acid loaded microparticles effect was very promising for its application as activators of salicylic acid dependent plant defense responses in lettuce as a model of horticultural plant species.