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Endophytic fungi can promote host plant growth, enhance antioxidant defense enzyme activity, and induce the biosynthesis and accumulation of secondarymetabolites. Therefore, using endophytic fungi to improve the quality and yield of medicinal plants or important crops is an effective means of regulation. Colletotrichum sp. AP12 has been reported to produce andrographolide compounds (ADCs). This study aimed to investigate the effects of AP12 and its elicitors on the growth, defense enzyme activity, accumulation, and transcription levels of key genes in Andrographis paniculata (Burm. f.) Nees ( A. paniculata ). Using fermentation method to prepare AP12 into the inactivated fermentation solution (IFS), fermentation solution (FS), inactivated mycelium solution (IMS), and mycelium solution (MS), and the results showed that all four fungal elicitor components (ECs) could promote A. paniculata growth, enhance antioxidant defense enzymes, and increase ADC content and yield, especially the IMS group that had the highest leaf area, whole plant dry weight, superoxide dismutase (SOD), catalase (CAT) enzyme activities, total lactone contents, and yields, which were 2.37-, 1.60-, 2.20-, 3.27-, 1.59-, and 2.65-fold of the control, respectively. The 14-deoxyandrographolide (NAD) in the host irrigated with MS was 3.35-fold that of the control. In addition, AP12-infected A. paniculata sterile seedlings could significantly increase ADC content and expression levels of key enzyme genes, especially on day 12, when the total lactone content of the host reached 88.881± 5.793 mg/g DW, while on day 6, CPS gene expression level reached 10.79-fold that of the control, in turn promoting the biosynthesis and accumulation of andrographolide. In conclusion, the endophytic fungus AP12 is beneficial to the growth and secondary metabolism of A. paniculata , which is helpful for the cultivation and application of the biological bacterial fertilizer in A. paniculata , providing a theoretical and research basis for the use of endophytic fungi as a microbial resource to improve the quality and yield of medicinal plants.

The use of seaweed-based bioproducts has been gaining momentum in crop production systems owing to their unique bioactive components and effects. They have phytostimulatory properties that result in increased plant growth and yield parameters in several important crop plants. They have phytoelicitor activity as their components evoke defense responses in plants that contribute to resistance to several pests, diseases, and abiotic stresses including drought, salinity, and cold. This is often linked to the upregulation of important defense-related genes and pathways in the plant system, priming the plant defenses against future attacks. They also evoke phytohormonal responses due to their specific components and interaction with plant growth regulation. Treatment by seaweed extracts and products also causes significant changes in the microbiome components of soil and plant in support of sustainable plant growth. Seaweed extracts contain a plethora of substances which are mostly organic, but trace levels of inorganic nutrient elements are also present. Fractionation of seaweed extracts into their components and their respective bioassays, however, has not yielded favorable growth effects. Only the whole seaweed extracts have been consistently proven to be very effective, which highlights the role of multiple components and their complex interactive effects on plant growth processes. Since seaweed extracts are highly organic, they are ideally suited for organic farming and environmentally sensitive crop production. They are also very compatible with other crop inputs, paving the way for an integrated management approach geared towards sustainability. The current review discusses the growth and functional effects evoked by seaweed extracts and their modes and mechanisms of action in crop plants which are responsible for elicitor and phytostimulatory activities. The review further analyses the potential value of seaweed extracts in integrated crop management systems towards sustainable crop production.

Pueraria tuberosa contains a wide range of bioactive compounds, including polyphenols, alkaloids, and phytosterols, which make it valuable to the pharmaceutical and food industries. Elicitor compounds trigger the defense mechanisms in plants and are widely used to increase the yield of bioactive molecules in in vitro cultures. The present study was conducted to evaluate the effects of different concentrations of biotic elicitors such as yeast extract (YE), pectin (PEC), and alginate (ALG) on growth, antioxidant activity, and metabolite accumulation in in vitro propagated shoots of P. tuberosa. The elicitors applied to shoot cultures of P. tuberosa significantly increased biomass (shoot number, fresh weight, and dry weight), and metabolites such as protein, carbohydrates, chlorophyll, total phenol (TP), and total flavonoid (TF) contents, as well as antioxidant activity compared to untreated control. Biomass, TP, and TF contents, as well as antioxidant activity, were most significant in cultures treated with 100 mg/L PEC. In contrast, chlorophyll, protein, and carbohydrate increased most in cultures treated with 200 mg/L ALG. Application of 100 mg/L of PEC led to the accumulation of high amounts of isoflavonoids including puerarin (220.69 μg/g), daidzin (2935.55 μg/g), genistin (5612 μg/g), daidzein (479.81 μg/g), and biochanin-A (111.511 μg/g) as analyzed by high-performance liquid chromatography (HPLC). Total isoflavonoids content of 100 mg/L PEC treated shoots was obtained as 9359.56 μg/g, 1.68-fold higher than in vitro propagated shoots without elicitors (5573.13 μg/g) and 2.77-fold higher than shoots of the mother plant (3380.17 μg/g). The elicitor concentrations were optimized as 200 mg/L YE, 100 mg/L PEC, and 200 mg/L ALG. Overall, this study showed that the application of different biotic elicitors resulted in better growth, antioxidant activity, and accumulation of metabolites in P. tuberosa, which could lead to obtaining phytopharmaceutical advantages in the future.

Malaxis acuminata D. Don [= Crepidium acuminatum (D. Don) Szlach.] is an important medicinal orchid used in various pharmaceutical preparations including “Ayurveda”. We report an improvised regeneration protocol for this prized orchid species using transverse thin cell layer (t-TCL) explants. The highest rate of shoot proliferation was recorded in the medium supplemented with meta-Topolin (mT) and chitosan at concentrations of 1.5 mg/l and 5.0 mg/l, respectively, wherein an average of 21 micro-shoots/explant were produced. The micro-shoots were transferred to rooting medium containing auxin [indole-3-butyric acid (IBA)/indole-3-acetic acid (IAA)] and phenolic elicitor [phloroglucinol (PG)]. The best rooting frequency was observed using 1.5 mg/l IBA and 5.0 mg/l PG in the culture medium. The regenerated plants with proliferated roots and shoots were acclimatized and survival rate was recorded. To evaluate the phytomedicinal efficiency of the micropropagated plants, flavonoid and phenolic compositions were determined using ultra performance liquid chromatography (UPLC). Four prominent fractions of metabolites were detected, of which the highest contents of quercetin and syringic acid were found in pseudobulbs and protocorm-like bodies (PLBs). Also, the highest antioxidant activities were recorded in the pseudobulb followed by PLB, leaf and whole plant extracts. The principal component analysis depicted the association between the plant organs/tissues and their metabolite contents. Furthermore, the expression levels of the five key modulator genes [viz. chalcone synthase (chs); phenylalanine ammonia lyase (pal); cinnamoyl-CoA reductase (ccr); hydroxymethylglutaryl-CoA-reductase (hmgr) and diphosphomevalonate decarboxylase (mvdd)] belonging to the flavonoid and phenolic acid biosynthetic pathways were studied in order to map the transcript abundance in various tissue parts of M. acuminata through quantitative real-time polymerase chain reaction (RT-qPCR). The present protocol can serve as a model approach for sustainable utilization of endangered orchid species of high industrial demand, strengthening the utility of chitosan as growth promoter in orchid micropropagation.Key messageThe research reports the use of meta-Topolin (mT)- chitosan synergy depicting gene-metabolite relation with the scope of adapting it as a model approach for bioprospection and conservation of orchids.

The present study aimed to develop a protocol for hairy root induction from Dracocephalum moldavica L.leaf explants and evaluate the effects of iron nanoparticles (Fe NPs) (0, 250, 500 and 1000 ppm), copper nanoparticles (Cu NPs) (0, 25, 50 and 100 ppm), and the combination of both (Fe/Cu NPs) on the antioxidant capacity, phenolic, flavonoids and rosmarinic acid content of hairy roots. Hairy root induction in D. moldavica was significantly ( P  ≤ 0.01) influenced by Agrobacterium rhizogenes strains, culture media and, sucrose concentration. The highest hairy root induction (86/6%) was related to the ATCC15834 strain on Murashige and Skoog culture medium supplemented with 30 g l − 1 sucrose. The individual and combined effects of the Fe and Cu NPs on the measured traits were highly significant ( P  ≤ 0.01). The highest amount of rosmarinic acid (26.38 mg/g DW) was obtained in the Cu NPs (100 ppm) with Fe NPs (1000 ppm) treatment, which was 6.6-fold higher compared to the control. The highest amount of flavonoids, malondialdehyde (MDA), phenolic compounds, hydrogen peroxide (H 2 O 2 ), proline, and anthocyanin production was obtained in the Cu NPs (100 ppm) + Fe NPs (1000 ppm) treatment that was 1.86, 1.56, 1.76, 2.07, 1.62, and 1.65-fold higher compared to respective control. Correlation and principal component analysis revealed a clear separation between the treatment groups and control, and also a positive correlation between rosmarinic acid production and other traits. The findings of this study indicated that the best results were obtained with the combined effect of Cu NPs (100 ppm) with Fe NPs (1000 ppm) treatment. Key message This is the first report on effect of iron and copper nanoparticles applied either alone or together on rosmarinic acid production and antioxidant capacity in Dracocephalum moldavica hairy roots. Graphical Abstract

A reduction in the lignin content in transgenic plants induces the ectopic expression of defense genes, but the importance of altered lignin composition in such phenomena remains unclear. Two Arabidopsis lines with similar lignin contents, but strikingly different lignin compositions, exhibited different quantitative and qualitative transcriptional responses. Plants with lignin composed primarily of guaiacyl units overexpressed genes responsive to oomycete and bacterial pathogen attack, whereas plants with lignin composed primarily of syringyl units expressed a far greater number of defense genes, including some associated with cis-jasmone-mediated responses to aphids; these plants exhibited altered responsiveness to bacterial and aphid inoculation. Several of the defense genes were differentially induced by water-soluble extracts from cell walls of plants of the two lines. Glycome profiling, fractionation and enzymatic digestion studies indicated that the different lignin compositions led to differential extractability of a range of heterogeneous oligosaccharide epitopes, with elicitor activity originating from different cell wall polymers. Alteration of lignin composition affects interactions with plant cell wall matrix polysaccharides to alter the sequestration of multiple latent defense signal molecules with an impact on biotic stress responses.

Pathogen-associated molecular patterns (PAMPs) are detected by plant pattern recognition receptors (PRRs), which gives rise to PAMP-triggered immunity (PTI). We characterized a novel fungal PAMP, Cell Death Inducing 1 (RcCDI1), identified in the Rhynchosporium commune transcriptome sampled at an early stage of barley (Hordeum vulgare) infection. The ability of RcCDI1 and its homologues from different fungal species to induce cell death in Nicotiana benthamiana was tested following agroinfiltration or infiltration of recombinant proteins produced by Pichia pastoris. Virus-induced gene silencing (VIGS) and transient expression of Phytophthora infestans effectors PiAVR3a and PexRD2 were used to assess the involvement of known components of PTI in N. benthamiana responses to RcCDI1. RcCDI1 was highly upregulated early during barley colonization with R. commune. RcCDI1 and its homologues from different fungal species, including Zymoseptoria tritici, Magnaporthe oryzae and Neurospora crassa, exhibited PAMP activity, inducing cell death in Solanaceae but not in other families of dicots or monocots. RcCDI1-triggered cell death was shown to require N. benthamiana Brassinosteroid insensitive 1-Associated Kinase 1 (NbBAK1), N. benthamiana suppressor of BIR1-1 (NbSOBIR1) and N. benthamiana SGT1 (NbSGT1), but was not suppressed by PiAVR3a or PexRD2. We report the identification of a novel Ascomycete PAMP, RcCDI1, recognized by Solanaceae but not by monocots, which activates cell death through a pathway that is distinct from that triggered by the oomycete PAMP INF1.

Background Rosaceae species are economically highly relevant crops. Their cultivation systems are constrained by phytopathogens causing severe losses. Plants respond to invading pathogens through signaling mechanisms, a component of which are of them being plant elicitor peptides (Peps). Exogenous application of Peps activates defense mechanisms and reduces the symptoms of pathogen infection in various pathosystems. We have previously identified the Rosaceae Peps and showed, in an ex vivo system, that their topical application efficiently enhanced resistance to the bacterial pathogen Xanthomonas arboricola pv. pruni (Xap). Results Here we demonstrate the effectiveness of Prunus persica peptides PpPep1 and PpPep2 in protecting peach plants in vivo at nanomolar doses, with 40% reduction of the symptoms following Xap massive infection. We used deep sequencing to characterize the transcriptomic response of peach plants to preventive treatment with PpPep1 and PpPep2. The two peptides induced highly similar massive transcriptomic reprogramming in the plant. One hour, 1 day and 2 days after peptide application there were changes in expression in up to 8% of peach genes. We visualized the transcriptomics dynamics in a background knowledge network and detected the minor variations between plant responses to PpPep1 and PpPep2, which might explain their slightly different protective effects. By designing a P. persica Pep background knowledge network, comparison of our data and previously published immune response datasets was possible. Conclusions Topical application of P. persica Peps mimics the PTI natural response and protects plants against massive Xap infection. This makes them good candidates for deployment of natural, targeted and environmental-friendly strategies to enhance resistance in Prunus species and prevent important biotic diseases.

Plant cell wall-derived oligosaccharides, i.e., damage-associated molecular patterns (DAMPs), could be generated after pathogen attack or during normal plant development, perceived by cell wall receptors, and can alter immunity and cell wall composition. Therefore, we hypothesised that xylo-oligosaccharides (XOS) could act as an elicitor and trigger immune responses. To test this, we treated Arabidopsis with xylobiose (XB) and investigated different parameters. XB-treatment significantly triggered the generation of reactive oxygen species (ROS), activated MAPK protein phosphorylation, and induced callose deposition. The combination of XB (DAMP) and flg22 a microbe-associated molecular pattern (MAMP) further enhanced ROS response and gene expression of PTI marker genes. RNA sequencing analysis revealed that more genes were differentially regulated after 30 min compared to 24 h XB-treated leaves, which correlated with ROS response. Increased xylosidase activity and soluble xylose level after 30 min and 3 h of XB-treatment were observed which might have weakened the DAMP response. However, an increase in total cell wall sugar and a decrease in uronic acid level was observed at both 30 min and 24 h. Additionally, arabinose, rhamnose, and xylose levels were increased in 30 min, and glucose was increased in 24 h compared to mock-treated leaves. The level of jasmonic acid, abscisic acid, auxin, and cytokinin were also affected after XB treatment. Overall, our data revealed that the shortest XOS can act as a DAMP, which triggers the PTI response and alters cell wall composition and hormone level.Key messageXylobiose treatment in Arabidopsis rosette leaf induces plant-triggered immunity (PTI) responses, alters cell wall polysaccharide composition and influences growth hormone levels.

Aims Due to its curative anti-cancer properties, the evergreen tree yew ( Taxus baccata L.) was well-known before recently. Water deficit is one of the most important environmental issues that has a detrimental influence on plant biochemical and physiological processes. By regulating plant processes at the molecular level, melatonin (MT), as a bioactive elicitor, helps plant growth and withstand stress. The goal of this research was to ascertain the impact of exogenous MT on several crucial phytochemical and physiological characteristics of yew under water scarcity. Methods Under drought stress conditions (40, 60, 80 and 100% Field capacity (FC)), MT was applied on the leaves of yew plants at concentrations of 100, 200, and 300 µM. Results Exogenous application of MT (200 µM) caused varied biochemical responses and the highest shoot and root weight in plants. During mild drought stress, MT application increased RWC and chlorophyl content. Also, MT-treated plants in conditions of moderate drought stress (i.e., 60% FC) had higher essential oil (EO) content and yield than untreated plants. α -Pinene and β -Myrcene, as two main compounds, were highest in plants not treated with melatonin under severe drought stress (40% FC). The highest E- β -Caryophyllene and α -Humulen (two other major components) were obtained from 200 µM and control, respectively, under 100% FC. Conclusions This research can be viewed as a useful approach to alleviate the negative impacts of water deficit stress, especially on pharmaceutical products, because the use of melatonin boosted the growth and phytochemical properties of yew in this work.