PR1 Expression Research Articles

NPR1 Promotes Its Own and Target Gene Expression in Plant Defense by Recruiting CDK8.

NPR1 (NONEXPRESSER OF PR GENES1) functions as a master regulator of the plant hormone salicylic acid (SA) signaling and plays an essential role in plant immunity. In the nucleus, NPR1 interacts with transcription factors to induce the expression of PR (PATHOGENESIS-RELATED) genes and thereby promote defense responses. However, the underlying molecular mechanism of PR gene activation is poorly understood. Furthermore, despite the importance of NPR1 in plant immunity, the regulation of NPR1 expression has not been extensively studied. Here, we show that SA promotes the interaction of NPR1 with both CDK8 (CYCLIN-DEPENDENT KINASE8) and WRKY18 (WRKY DNA-BINDING PROTEIN18) in Arabidopsis (Arabidopsis thaliana). NPR1 recruits CDK8 and WRKY18 to the NPR1 promoter, facilitating its own expression. Intriguingly, CDK8 and its associated Mediator subunits positively regulate NPR1 and PR1 expression and play a pivotal role in local and systemic immunity. Moreover, CDK8 interacts with WRKY6, WRKY18, and TGA transcription factors and brings RNA polymerase II to NPR1 and PR1 promoters and coding regions to facilitate their expression. Our studies reveal a mechanism in which NPR1 recruits CDK8, WRKY18, and TGA transcription factors along with RNA polymerase II in the presence of SA and thereby facilitates its own and target gene expression for the establishment of plant immunity.

The Arabidopsis Lectin Receptor Kinase LecRK-I.8 Is Involved in Insect Egg Perception.

Plants induce defense responses after insect egg deposition, but very little is known about the perception mechanisms. In Arabidopsis thaliana, eggs of the specialist insect Pieris brassicae trigger accumulation of reactive oxygen species (ROS) and salicylic acid (SA), followed by induction of defense genes and localized necrosis. Here, the involvement of the clade I L-type lectin receptor kinase LecRK-I.8 in these responses was studied. Expression of LecRK-I.8 was upregulated at the site of P. brassicae oviposition and egg extract (EE) treatment. ROS, SA, cell death, and expression of PR1 were substantially reduced in the Arabidopsis knock-out mutant lecrk-I.8 after EE treatment. In addition, EE-induced systemic resistance against Pseudomonas syringae was abolished in lecrk-I.8. Expression of ten clade I homologs of LecRK-I.8 was also induced by EE treatment, but single mutants displayed only weak alteration of EE-induced PR1 expression. These results demonstrate that LecRK-I.8 is an early component of egg perception.

Identification and Functional Characterization of an Effector Secreted by Cronartium ribicola

Cri-9402 was identified as a protein effector from Cronartium ribicola, based on the effect of its expression on growth of Pseudomonas syringae Psm ES4326 introduced into transiently transformed tobacco leaves and stably transformed Arabidopsis seedlings. In tobacco leaves transiently expressing its coding sequence, growth of P. syringae Psm ES4326 was inhibited. Expression of pathogenesis-related (PR) protein 2 (PR2), PR4a, endochitinase B, hypersensitive-related 201 (HSR201), HSR203J, and proteinase inhibitor 1 was upregulated but expression of PR1, coronatine insensitive 1, and abscisic acid 1 was significantly suppressed. In transformed Arabidopsis seedlings, the effector stimulated growth of P. syringae Psm ES4326; significantly suppressed expression of PR1, PR2, nonexpresser of pathogenesis-related genes 1 (NPR1), NPR3, NPR4, phytoalexin deficient 4, and salicylic acid induction deficient 2; and enhanced expression of plant defensin 1.2 (PDF1.2). The above results showed that the majority of responses to this effector in tobacco leaves were converse to those in transformed Arabidopsis. We could conclude that Cri-9402 promoted disease resistance in tobacco leaves and disease susceptibility in Arabidopsis seedlings. Its transcript was mainly expressed in aeciospores of C. ribicola and was probably involved in production or germination of aeciospores, and it was an effector potentially functioning in white pine-blister rust interactions.

Activity in the Arbuscular Mycorrhizal Hyphosphere Warning Neighbouring Plants.

Pathogen infections of the phyllosphere have been investigated in detail, however, the changes induced by these infections on the arbuscular mycorrhizal hyphosphere, and the consequent signalling to the neighbouring plants have been scarcely investigated. Here, our objectives were to document that B.fabae infection of connected Vicia faba plants resulted in changes in the metabolism and microbial community of the hyphosphere, confirming the induction of plant defence in connected plants through gene-expression evaluations. Infected plants were challenged with B. fabae for 72 h. Changes in gene-expression of pathogenesis-related proteins 1,2, and 5 (PR1, PR2, PR5) of both infected- and non-infected plants were analysed, to confirm signalling through the hyphosphere. The primary metabolic profiles and changes in the level of microbiota in the hyphosphere were assessed. Changes in expression of PR1, PR2, and PR5 genes occurred in the neighbouring plants 24 hours after infection. Mannitol levels decreased in presence of AMF. A decrease in the level of actinobacteria in the hyphosphere of infected plants was detected. We conclude that B.fabae infection induced a signalling event through the AM hyphosphere, confirmed by changes in defence gene-expression in non-infected neighbouring plants, influenced primary metabolic activity of-, and affected the microbial composition within-, the AM hyphosphere.

Isolation and characterization of the GbVIP1 gene and response to Verticillium wilt in cotton and tobacco

BackgroundVerticillium wilt is a serious soil-borne vascular disease that causes major losses to upland cotton (Gossypium hirutum L.) worldwidely every year. The protein VIP1 (VirE2 interaction protein 1), a bZIP transcription factor, is involved in plant response to many stress conditions, especially pathogenic bacteria. However, its roles in cotton response to Verticillium wilt are poorly understood.ResultsThe GbVIP1 gene was cloned from resistant sea-island cotton (G. barbadense) cv. Hai 7124. Expression of GbVIP1 was up-regulated by inoculation with Verticillium dahliae and exogenous treatment with ethylene. Results of virus-induced gene silencing suggested that silencing of GbVIP1 weakened cotton resistance to Verticillium wilt. The heterologous expression of GbVIP1 in tobacco showed enhanced resistance to Verticillium wilt. The PR1, PR1-like and HSP70 genes were up-regulated in GbVIP1 transgenic tobacco after Verticillium wilt infection.ConclusionOur results suggested that GbVIP1 increased plant resistance to Verticillium wilt through up-regulating expressions of PR1, PR1-like, and HSP70. These results provide new approaches to improving resistance to Verticillium wilt in upland cotton and also have great potential for disease-resistance breeding of cotton.

Bacillus amyloliquefaciens Ba13 induces plant systemic resistance and improves rhizosphere microecology against tomato yellow leaf curl virus disease

The control effect of Bacillus against tomato yellow leaf curl virus (TYLCV) disease has not been reported. It is not clear whether adjustment of the rhizosphere microbial community structure by beneficial microbes applied as biocontrol agents is related to their role in increasing resistance of plants to viral diseases. Therefore, the objective of this study was to investigate the control effect and mechanism of Bacillus amyloliquefaciens Ba13 against TYLCV disease. Two treatments including control and Ba13 treatment followed by natural infection with whiteflies were conducted. We measured plant growth, physiological parameters, disease severity, and leaf virus quantity and also assayed resistance-related gene expression, defense enzyme activity, and rhizosphere microbial community structure. Strain Ba13 lowered the infection rate, disease severity, and leaf virus quantity in tomato plants, with the control rate of 48–52%. Root development and shoot biomass markedly improved in tomato following Ba13 treatment. Ba13 elevated expression of pathogenesis-related PR1, PR2, and PR3 genes, and enhanced activities of phenylalanine ammonia lyase, polyphenol oxidase, peroxidase, β-1,3 glucanase, and chitinase in tomato leaves. Cultivation-dependent microbiological analysis showed that Ba13 increased the bacteria-to-fungi ratio and the number of beneficial microbes while decreasing the number of pathogenic fungi in the rhizosphere. Further analysis revealed the potential of a dominant rhizosphere bacterium, B. velezensis B3, to promote plant growth and improve systemic resistance in tomato. B. amyloliquefaciens Ba13 can enhance plant resistance against TYLCV disease through direct induction of systemic resistance and also by increasing the number of beneficial microbes in the rhizosphere, thereby achieving control of TYLCV disease.

Bacillus subtilis PTA-271 Counteracts Botryosphaeria Dieback in Grapevine, Triggering Immune Responses and Detoxification of Fungal Phytotoxins.

Plant pathogens have evolved various strategies to enter hosts and cause diseases. Particularly Neofusicoccum parvum, a member of Botryosphaeria dieback consortium, can secrete the phytotoxins (-)-terremutin and (R)-mellein during grapevine colonization. The contribution of phytotoxins to Botryosphaeria dieback symptoms still remains unknown. Moreover, there are currently no efficient control strategies of this disease, and agro-environmental concerns have raised increasing interest in biocontrol strategies to limit disease spread in vineyards, especially by using some promising beneficial bacteria. Here, we first examined in planta the biocontrol capacity of Bacillus subtilis PTA-271 against N. parvum Np-Bt67 strain producing both (-)-terremutin and (R)-mellein. We then focused on the direct effects of PTA-271 on pathogen growth and the fate of pure phytotoxins, and explored the capacity of PTA-271 to induce or prime grapevine immunity upon pathogen infection or phytotoxin exposure. Results provided evidence that PTA-271 significantly protects grapevine cuttings against N. parvum and significantly primes the expression of PR2 (encoding a β-1,3-glucanase) and NCED2 (9-cis-epoxycarotenoid dioxygenase involved in abscisic acid biosynthesis) genes upon pathogen challenge. Using in vitro plantlets, we also showed that PTA-271 triggers the expression of salicylic acid- and jasmonic acid-responsive genes, including GST1 (encoding a glutathione-S-transferase) involved in detoxification process. However, in PTA-271-pretreated plantlets, exogenous (-)-terremutin strongly lowered the expression of most of upregulated genes, except GST1. Data also indicated that PTA-271 can detoxify both (-)-terremutin and (R)-mellein and antagonize N. parvum under in vitro conditions. Our findings highlight (-)-terremutin and (R)-mellein as key aggressive molecules produced by N. parvum that may weaken grapevine immunity to promote Botryosphaeria dieback symptoms. However, PTA-271 can efficiently attenuate Botryosphaeria dieback by enhancing some host immune responses and detoxifying both phytotoxins produced by N. parvum.

Mutualistic co-evolution of T3SSs during the establishment of symbiotic relationships between Vigna radiata and Bradyrhizobia.

This study supports the idea that the evolution of type III secretion system (T3SS) is one of the factors that controls Vigna radiata–bradyrhizobia symbiosis. Based on phylogenetic tree data and gene arrangements, it seems that the T3SSs of the Thai bradyrhizobial strains SUTN9‐2, DOA1, and DOA9 and the Senegalese strain ORS3257 may share the same origin. Therefore, strains SUTN9‐2, DOA1, DOA9, and ORS3257 may have evolved their T3SSs independently from other bradyrhizobia, depending on biological and/or geological events. For functional analyses, the rhcJ genes of ORS3257, SUTN9‐2, DOA9, and USDA110 were disrupted. These mutations had cultivar‐specific effects on nodulation properties. The T3SSs of ORS3257 and DOA9 showed negative effects on V. radiata nodulation, while the T3SS of SUTN9‐2 showed no effect on V. radiata symbiosis. In the roots of V. radiata CN72, the expression levels of the PR1 gene after inoculation with ORS3257 and DOA9 were significantly higher than those after inoculation with ORS3257 ΩT3SS, DOA9 ΩT3SS, and SUTN9‐2. The T3Es from ORS3257 and DOA9 could trigger PR1 expression, which ultimately leads to abort nodulation. In contrast, the T3E from SUTN9‐2 reduced PR1 expression. It seems that the mutualistic relationship between SUTN9‐2 and V. radiata may have led to the selection of the most well‐adapted combination of T3SS and symbiotic bradyrhizobial genotype.

GbWRKY1, a member of the WRKY transcription factor family identified from Gossypium barbadense, is involved in resistance to Verticillium wilt

WRKY transcription factors are involved in complex signalling processes that occur during stress responses. However, in contrast to the exploration of such mechanisms in model plants, far less research has focussed on the WRKY family in cotton. We previously identified GbWRKY1 in cotton (Gossypium barbadense), the expression of which is induced upon infection by Verticillium dahliae. Our current results indicate that this gene with three introns, has a group of cis-acting elements in its promoter that are associated with plant growth and development as well as responses to environmental stresses. Here, we used virus-induced gene silencing to characterize the role of GbWRKY1. Silencing in cotton simultaneously up-regulated salicylic acid (SA)-mediated responses and inhibited jasmonate (JA)-inducible and ethylene (ET)-inducible defences, resulting in an increased susceptibility to V. dahliae. However, when compared with wild-type Arabidopsis, transgenic plants exhibited more resistance to infection with V. dahliae. In the latter genotype, expression was increased for pathogen-related PR4 and ACS2, two genes involved in the JA pathway and ET biosynthesis, while expression of PR5, involved in the SA pathway, decreased after V. dahliae infection. Moreover, POD activity and lignin content related to ethylene synthesis in transgenic Arabidopsis were higher than those in wild-type Arabidopsis after V. dahliae infection. Collectively, these findings suggest that GbWRKY1 is regulated by signalling pathways for SA, JA and ET, and mainly involved in resistance to V. dahliae attack by ET signalling pathway the response. This highlights the importance of WRKYs in regulating pathogen-induced responses and plant development.

Evaluation of Immune Responses Induced by Simultaneous Inoculations of Soybean (Glycine max [L.] Merr.) with Soil Bacteria and Rhizobia.

Legumes form root nodules and fix atmospheric nitrogen by establishing symbiosis with rhizobia. However, excessive root nodules are harmful to plants because of the resulting overconsumption of energy from photosynthates. The delay of an inoculation of the soybean super-nodulation mutant NOD1–3 with Bradyrhizobium diazoefficiens USDA110T by 5 d after an inoculation with several soil bacteria confirmed that one bacterial group significantly decreased root nodules throughout the study period. Moreover, no significant changes were observed in nitrogen fixation by root nodules between an inoculation with USDA 110T only and co-inoculation treatments. To clarify the potential involvement of PR proteins in the restriction of nodule formation in the plants tested, the relative expression levels of PR-1, PR-2, PR-5, and PDF1.2 in NOD1–3 roots were measured using real-time PCR. One group of soil bacteria (Gr.3), which markedly reduced nodule numbers, significantly induced the expression of PR-1, PR-5 and PDF1.2 genes by day 5 after the inoculation. By days 7, 10, and 20 after the inoculation, the expression levels of PR-2 and PR-5 were lower than those with the uninoculated treatment. Inoculations with this group of soil bacteria resulted in lower root nodule numbers than with other tested soil bacteria exerting weak inhibitory effects on nodulation, and were accompanied by the induction of plant defense-related genes. Thus, PR genes appear to play important roles in the mechanisms that suppresses nodule formation on soybean roots.

Identification of Long Noncoding RNA-Protein Interactions Through In Vitro RNA Pull-Down Assay with Plant Nuclear Extracts.

Recent advances in next-generation sequencing have revealed that majority of the plant genome is transcribed into long noncoding RNA (lncRNA). Many lncRNAs function by interacting with proteins and forming regulatory complexes. RNA-protein interactions are vital in controlling core cellular processes like transcription and translation. Therefore, identifying proteins that interact with lncRNAs is the first step to deciphering lncRNA functions. Here, we describe an RNA-protein pull-down assay, which enables the identification of proteins that interact with an RNA under study. As an example, we describe pull-down of proteins interacting with lncRNA ELENA1, which promotes the enrichment of MED19a on PR1 promoter to activate PR1 expression.

Gene network mediated by WRKY13 to regulate resistance against sheath infecting fungi in rice (Oryza sativa L.)

OsWRKY13 TF gene is known to play a regulatory role of signaling in physiological pathways related to either development or disease resistance in rice plants. Rice cultivars IR 50 and TRY 3, resistant and susceptible respectively to sheath blight, TRY 3 and CO 43 resistant and susceptible respectively to sheath rot were challenged with fungal pathogens and disease scoring was carried out. Percent Disease Index (PDI) was significantly higher in susceptible varieties than resistant varieties. RT-PCR and qPCR analyses of WRKY13 using RNA extracted from the plant tissues revealed higher WRKY13 expression in resistant varieties (both diseases) upon pathogen challenge compared to uninfected control and also the susceptible varieties. To compute and evaluate the possible molecular mechanism for observed resistance correlated to WRKY13 gene expression, rice gene expression profiles against bacterial leaf blight and leaf blast disease from ROAD database were used to prioritize the locus IDs that were used as input in RiceNet v2 tool. The expression of WRKY13-regulated TIFY9 gene was predicted and validated using RT-PCR and qRT-PCR along with WRKY12 and PR2. All three genes showed induced expression in R. solani challenged sheath blight resistant variety. WRKY12 and PR2 expression in S. oryzae challenged sheath rot resistant variety was higher. Agrobacterium mediated transformation was carried out in rice plants using overexpression construct of WRKY13 (agroinfection in seeds of varieties susceptible to sheath blight and sheath rot, followed by selection in antibiotic media, germinating and hardening of putative transgenic lines). Based on qPCR analysis, the expression level of WRKY13 and the co-expression levels of WRKY12, TIFY9 and PR2 were found higher in PCR-positive T1 plants compared to wild-type. Infection bioassays in the transgenic plants of both varieties revealed enhanced resistance to the pathogens. A mechanism by which WRKY13 would influence the MAPK cascade with TIFY9 acting as a mediator, is proposed.

Biological Control of Pierce's Disease of Grape by an Endophytic Bacterium.

Effective preventive measures and therapies are lacking for control of Pierce's disease of grape caused by the xylem-colonizing bacterium Xylella fastidiosa responsible for serious losses in grape production. In this study we explored the potential for endophytic bacteria to alter the disease process. While most endophytic bacteria found within grape did not grow or multiply when inoculated into mature grape vines, Paraburkholderia phytofirmans strain PsJN achieved population sizes as large as 106 cells/g and moved 1 m or more within 4 weeks after inoculation into vines. While X. fastidiosa achieved large population sizes and moved extensively in grape when inoculated alone, few viable cells were recovered from plants in which it was co-inoculated with strain PsJN and the incidence of leaves exhibiting scorching symptoms typical of Pierce's disease was consistently greatly reduced from that in control plants. Suppression of disease symptoms occurred not only when strain PsJN was co-inoculated with the pathogen by puncturing stems in the same site in plants, but also when inoculated at the same time but at different sites in the plant. Large population sizes of strain PsJN could be established in both leaf lamina and petioles by topical application of cell suspensions in 0.2% of an organo-silicon surfactant conferring low surface tension, and such treatments were as effective as direct puncture inoculations of this biocontrol strain in reducing disease severity. While inoculation of strain PsJN into plants by either method at the same time as or even 4 weeks after that of the pathogen resulted in large reductions in disease severity, much less disease control was conferred by inoculation of PsJN 4 weeks prior to that of the pathogen. The expression of grapevine PR1 and ETR1 within 3 weeks of inoculation was substantially higher in plants inoculated with both X. fastidiosa and strain PsJN compared with that in plants inoculated only with the pathogen or strain PsJN, suggesting that this biological control agent reduces disease by priming expression of innate disease resistance pathways in plants that otherwise would have exhibited minimal responses to the pathogen. Strain PsJN thus appears highly efficacious for the control of Pierce's disease when used as an eradicant treatment that can be easily made even by spray application.

Insect egg deposition renders plant defence against hatching larvae more effective in a salicylic acid-dependent manner.

Plants can improve their antiherbivore defence by taking insect egg deposition as cue of impending feeding damage. Previous studies showed that Pieris brassicae larvae feeding upon egg-deposited Brassicaceae perform worse and gain less weight than larvae on egg-free plants. We investigated how P.brassicae oviposition on Arabidopsis thaliana affects the plant's molecular and chemical responses to larvae. A transcriptome comparison of feeding-damaged leaves without and with prior oviposition revealed about 200 differently expressed genes, including enhanced expression of PR5, which is involved in salicylic acid (SA)-signalling. SA levels were induced by larval feeding to a slightly greater extent in egg-deposited than egg-free plants. The adverse effect of egg-deposited wild-type (WT) plants on larval weight was absent in an egg-deposited PR5-deficient mutant or other mutants impaired in SA-mediated signalling, that is, sid2/ics1, ald1, and pad4. In contrast, the adverse effect of egg-deposited WT plants on larvae was retained in egg-deposited npr1 and wrky70 mutants impaired further downstream in SA-signalling. Oviposition induced accumulation of flavonols in WT plants with and without feeding damage, but not in the PR5-deficient mutant. We demonstrated that egg-mediated improvement of A.thaliana's antiherbivore defence involves SA-signalling in an NPR1-independent manner and is associated with accumulation of flavonols.

PFLP-Intensified Disease Resistance Against Bacterial Soft Rot Through the MAPK Pathway in PAMP-Triggered Immunity

Bacterial soft rot is a devastating disease affecting a variety of vegetable crops worldwide. One strategy for controlling this disease could be the ectopic expression of the plant ferredoxin-like protein (pflp) gene. PFLP was previously shown to intensify pathogen-associated molecular pattern-triggered immunity (PTI), an immune response triggered, for example, by the flagellin epitope flg22. To gain further insight into how PFLP intensifies PTI, flg22 was used as an elicitor in Arabidopsis thaliana. First, PFLP was confirmed to intensify the rapid generation of H2O2, callose deposition, and the hypersensitive response when coinfiltrated with flg22. This response correlated with increased expression of the FLG22-induced receptor kinase 1 gene, which is part of the mitogen-activated protein kinase (MAPK) pathway. Although the increased response to flg22 alone did not depend on the MAPK pathway genes MEKK1, MKK5, and MPK6, the protective effect of PFLP decreased when plants mutated in these genes were inoculated with Pectobacterium carotovorum subsp. carotovorum. Furthermore, expression of PR1 and PDF1.2 also increased upon treatment with flg22 in the presence of PFLP. Taken together, these results suggest that activation of the MAPK pathway contributes to the increased resistance to bacterial soft rot observed in plants treated with PFLP.

Identification of a strawberry NPR-like gene involved in negative regulation of the salicylic acid-mediated defense pathway.

Hormonal modulation plays a central role in triggering various resistant responses to biotic and abiotic stresses in plants. In cultivated strawberry (Fragaria x ananassa), the salicylic acid (SA)-dependent defense pathway has been associated with resistance to Colletotrichum spp. and the other pathogens. To better understand the SA-mediated defense mechanisms in strawberry, we analyzed two strawberry cultivars treated with SA for their resistance to anthracnose and gene expression profiles at 6, 12, 24, and 48 hr post-treatment. Strawberry genes related to SA biosynthesis, perception, and signaling were identified from SA-responsive transcriptomes of the two cultivars, and the induction of 17 candidate genes upon SA treatment was confirmed by qRT-PCR. Given the pivotal role of the non-expressor of pathogenesis-related (NPR) family in controlling the SA-mediated defense signaling pathway, we then analyzed NPR orthologous genes in strawberry. From the expression profile, FaNPRL-1 [ortholog of FvNPRL-1 (gene20070 in F. vesca)] was identified as an NPR-like gene significantly induced after SA treatment in both cultivars. With a conserved BTB/POZ domain, ankyrin repeat domain, and nuclear localization signal, FvNPRL-1 was found phylogenetically closer to NPR3/NPR4 than NPR1 in Arabidopsis. Ectopic expression of FvNPRL-1 in the Arabidopsis thaliana wild type suppressed the SA-mediated PR1 expression and the resistance to Pseudomonas syringae pv. tomato DC3000. Transient expression of FvNPRL-1 fused with green fluorescent protein in Arabidopsis protoplasts showed that SA affected nuclear translocation of FvNPRL-1. FvNPRL-1 likely functions similar to Arabidopsis NPR3/NPR4 as a negative regulator of the SA-mediated defense.

Aphid infestation in the phyllosphere affects primary metabolic profiles in the arbuscular mycorrhizal hyphosphere

While effects of (a)biotic stress events in the phyllosphere have been studied intensively, possible influences of stress on the arbuscular mycorrhizal hyphosphere has scarcely been investigated. We hypothesised that stress challenge in the phyllosphere could alter primary metabolite profiles of the hyphosphere - the mycelial network connecting plants. Donor plants, connected to receiver plants by mycelial networks, were aphid-challenged during 84 h. Primary metabolite profiles in the hyphosphere were investigated. Gene-expression of plant defence gene PR1 was measured in one of the receiver plants during the challenge. Hexose levels in the hyphosphere increased when donor plants were aphid-challenged. This change in metabolic profile was influenced by leaf sampling from receiver plant. PR1 expression increased in donor plants 48 h after challenge, and consequently 60 h after, in receiver plants. We conclude that aphid infestation of donor plants modified primary carbon metabolism in the hyphosphere. Plant defence response in receiver plants, occurred 12 h after detection of response in the aphid-challenged donor plants. While this work is the first to reveal primary metabolic profiles of the AM hyphosphere, more work is needed to elucidate the possible role of transient changes of hexose metabolism in stress response and signalling processes in the hyphosphere of connected plants.

Characterization of salicylic acid-mediated modulation of the drought stress responses: Reactive oxygen species, proline, and redox state in Brassica napus

The goal of this study was to characterize hormonal regulation of drought stress-induced responses and salicylic acid (SA)-mediated stress responses, focusing on redox control. The responses of reactive oxygen species (ROS) and proline metabolism, antioxidant activity, and redox status to SA pretreatment and/or drought imposition were interpreted as being linked to those of endogenous hormonal levels and their signaling genes, especially in redox control processes. Drought enhanced the endogenous levels of abscisic acid (ABA) and jasmonic acid (JA) resulting in an increase of ABA/SA and (ABA + JA)/SA. The changes in endogenous hormonal balance were concomitant with an accumulation of ROS and proline, accompanied by a loss of reducing potential [NAD(P)H/NAD(P)+ and GSH/GSSG]. SA pretreatment scavenged drought-induced O2− accumulation (but not H2O2) and led to an additional proline accumulation with enhanced expression of proline synthesis-related genes (P5CS1, P5CS2 and P5CR) and NADPH oxidase, and a reset of reducing potential with enhanced expression of redox regulating genes (TRXh5 and GRXC9). SA-mediated stress responses coincided with the enhanced expression of NPR1 and PR-1, with an antagonistic depression of ABA- and JA-related genes (NCED3, MYC2, and PDF1.2). These results indicate that the SA-modulated NPR1-dependent signalling pathway and proline synthesis are an integrative process of redox control under drought.

Salicylic acid in Populus tomentosa is a remote signalling molecule induced by Botryosphaeria dothidea infection

The salicylic acid (SA) plays a critical role during the establishment of systemic acquired resistance (SAR) in uninfected plant tissues after localised exposure to a pathogen. Here, we studied SA in Populus tomentosa infected by the plant pathogen Botryosphaeria dothidea. The accumulation of SA and methyl salicylate (MeSA) occurred in chronological order in P. tomentosa. The SA and MeSA contents were greater at infected than uninfected sites. Additionally, a gene expression analysis indicated that SA might be accumulated by phenylalanine ammonialyase (PAL) and converted to MeSA by SA carboxyl methyltransferase (SAMT), while MeSA might convert to SA by SA-binding protein 2 (SABP2). The expressions of SAMT at infected sites and SABP2 at uninfected sites, respectively, were significantly up-regulated. Thus, SA might be converted to MeSA at infected sites and transported as a signalling molecule to uninfected sites, where it is converted to SA for SAR. Moreover, the expressions of pathogenesis-related genes PR-1, PR-2 and PR-5 in P. tomentosa were up-regulated by the B. dothidea infection. Our study determined that variations in SA and MeSA contents occur at infected and uninfected sites in poplar after pathogen infection and contributed to the remote signals for poplar SAR.

Species-specific plant\u2013soil feedbacks alter herbivore-induced gene expression and defense chemistry in Plantago lanceolata

Plants actively interact with antagonists and beneficial organisms occurring in the above- and belowground domains of terrestrial ecosystems. In the past decade, studies have focused on the role of plant–soil feedbacks (PSF) in a broad range of ecological processes. However, PSF and its legacy effects on plant defense traits, such as induction of defense-related genes and production of defensive secondary metabolites, have not received much attention. Here, we study soil legacy effects created by twelve common grassland plant species on the induction of four defense-related genes, involved in jasmonic acid signaling, related to chewing herbivore defense (LOX2, PPO7), and in salicylic acid signaling, related to pathogen defense (PR1 and PR2) in Plantago lanceolata in response to aboveground herbivory by Mamestra brassicae. We also assessed soil legacy and herbivory effects on the production of terpenoid defense compounds (the iridoid glycosides aucubin and catalpol) in P. lanceolata. Our results show that both soil legacy and herbivory influence phenotypes of P. lanceolata in terms of induction of Pl PPO7 and Pl LOX2, whereas the expression of Pl PR1 and Pl PR2-1 is not affected by soil legacies, nor by herbivory. We also find species-specific soil legacy effects on the production of aucubin. Moreover, P. lanceolata accumulates more catalpol when they are grown in soils conditioned by grass species. Our study highlights that PSF can influence aboveground plant–insect interactions through the impacts on plant defense traits and suggests that aboveground plant defense responses can be determined, at least partly, by plant-specific legacy effects induced by belowground organisms.