Coordinated plant defense responses in Arabidopsis revealed by microarray analysis

Bacterial growth-mediated systems remodelling of Nicotiana benthamiana defines unique signatures of target protein production in molecular pharming

The need for therapeutics to treat a plethora of medical conditions and diseases is on the rise and the demand for alternative approaches to mammalian-based production systems is increasing. Plant-based strategies provide a safe and effective alternative to produce biological drugs but have yet to enter mainstream manufacturing at a competitive level. Limitations associated with batch consistency and target protein production levels are present; however, strategies to overcome these challenges are underway. In this study, we apply state-of-the-art mass spectrometry-based proteomics to define proteome remodelling of the plant following agroinfiltration with bacteria grown under shake flask or bioreactor conditions. We observed distinct signatures of bacterial protein production corresponding to the different growth conditions that directly influence the plant defence responses and target protein production on a temporal axis. Our integration of proteomic profiling with small molecule detection and quantification reveals the fluctuation of secondary metabolite production over time to provide new insight into the complexities of dual system modulation in molecular pharming. Our findings suggest that bioreactor bacterial growth may promote evasion of early plant defence responses towards Agrobacterium tumefaciens (updated nomenclature to Rhizobium radiobacter). Furthermore, we uncover and explore specific targets for genetic manipulation to suppress host defences and increase recombinant protein production in molecular pharming.

OsEIL2 balances rice immune responses against (hemi)biotrophic and necrotrophic pathogens via the salicylic acid and jasmonic acid synergism

Plants typically activate distinct defense pathways against various pathogens. Heightened resistance to one pathogen often coincides with increased susceptibility to another pathogen. However, the underlying molecular basis of this antagonistic response remains unclear. Here, we demonstrate that mutants defective in the transcription factor ETHYLENE-INSENSITIVE 3-LIKE 2 (OsEIL2) exhibited enhanced resistance to the biotrophic bacterial pathogen Xanthomonas oryzae pv oryzae and to the hemibiotrophic fungal pathogen Magnaporthe oryzae, but enhanced susceptibility to the necrotrophic fungal pathogen Rhizoctonia solani. Furthermore, necrotroph-induced OsEIL2 binds to the promoter of OsWRKY67 with high affinity, leading to the upregulation of salicylic acid (SA)/jasmonic acid (JA) pathway genes and increased SA/JA levels, ultimately resulting in enhanced resistance. However, biotroph- and hemibiotroph-induced OsEIL2 targets OsERF083, resulting in the inhibition of SA/JA pathway genes and decreased SA/JA levels, ultimately leading to reduced resistance. Our findings unveil a previously uncharacterized defense mechanism wherein two distinct transcriptional regulatory modules differentially mediate immunity against pathogens with different lifestyles through the transcriptional reprogramming of phytohormone pathway genes.

CmPIF8-CmERF27-CmACS10-mediated ethylene biosynthesis modulates red light-induced powdery mildew resistance in oriental melon

Powdery mildew is a serious fungal disease in protected melon cultivation that affects the growth, development and production of melon plants. Previous studies have shown that red light can improve oriental melon seedlings resistance to powdery mildew. Here, after inoculation with Podosphaera xanthii, an obligate fungal pathogen eliciting powdery mildew, we found that red light pretreatment increased ethylene production and this improved the resistance of melon seedlings to powdery mildew, and the ethylene biosynthesis gene CmACS10 played an important role in this process. By analysing the CmACS10 promoter, screening yeast one-hybrid library, it was found that CmERF27 positively regulated the expression of CmACS10, increased powdery mildew resistance and interacted with PHYTOCHROME INTERACTING FACTOR8 (CmPIF8) at the protein level to participate in the regulation of ethylene biosynthesis to respond to the red light-induced resistance to P. xanthii, Furthermore, CmPIF8 also directly targeted the promoter of CmACS10, negatively participated in this process. In summary, this study revealed the specific mechanism by which the CmPIF8-CmERF27-CmACS10 module regulates red light-induced ethylene biosynthesis to resist P. xanthii infection, elucidate the interaction between light and plant hormones under biological stress, provide a reference and genetic resources for breeding of disease-resistant melon plants.

MdPRX34L, a class III peroxidase gene, activates the immune response in apple to the fungal pathogen Botryosphaeria dothidea

MAIN CONCLUSION

MdPRX34L enhanced resistance to Botryosphaeria dothidea by increasing salicylic acid (SA) and abscisic acid (ABA) content as well as the expression of related defense genes. The class III peroxidase (PRX) multigene family is involved in complex biological processes. However, the molecular mechanism of PRXs in the pathogen defense of plants against Botryosphaeria dothidea (B. dothidea) remains unclear. Here, we cloned the PRX gene MdPRX34L, which was identified as a positive regulator of the defense response to B. dothidea, from the apple cultivar 'Royal Gala.' Overexpression of MdPRX34L in apple calli decreased sensitivity to salicylic acid (SA) and abscisic acid（ABA). Subsequently, overexpression of MdPRX34L in apple calli increased resistance to B. dothidea infection. In addition, SA contents and the expression levels of genes related to SA synthesis and signaling in apple calli overexpressing MdPRX34L were higher than those in the control after inoculation, suggesting that MdPRX34L enhances resistance to B. dothidea via the SA pathway. Interestingly, infections in apple calli by B. dothidea caused an increase in endogenous levels of ABA followed by induction of ABA-related genes expression. These findings suggest a potential mechanism by which MdPRX34L enhances plant-pathogen defense against B. dothidea by regulating the SA and ABA pathways.

Metarhabditis amsactae: A potential biopesticide isolated from Punjab (India) with potent insecticidal activity and immunomodulatory effects against Galleria mellonella (Lepidoptera: Pyralidae)

A survey was undertaken to isolate entomopathogenic nematodes from Amritsar district of Punjab, India. Out of 20 soil samples collected, two were found positive for the presence of nematodes. 18S and ITS rDNA gene sequencing revealed their identity as Metarhabditis amsactae. To assess its biocontrol potential, Galleria mellonella larvae were treated with concentrations of 20, 40, 80 and 160 IJs/L (infective juveniles/larva) and mortality was recorded from 24 h up to 96 h of nematode exposure. Distilled water without nematodes was used as an untreated control. M. amsactae showed potent larvicidal activity against G. mellonella that was found to be concentration and time dependent. Nematode infection caused 93.33 % larval mortality at 80 IJs/L after 72 h of treatment. 100 % mortality was observed after 96 h. No mortality was observed in control. To evaluate the immunomodulatory effects of M. amsactae, G. mellonella larvae were infected with 100 IJs/L and activities of antioxidant and detoxifying enzymes viz., superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX), phenol oxidase (PO), glutathione-S-transferase (GST) and acetylcholine esterase (AChE) were appraised after 12, 24, 36 and 48 h of nematode exposure. Malondialdehyde content was also determined. The results obtained demonstrated a significant elevation in all the enzyme activities at all time intervals in treated larvae when compared with untreated control. MDA levels were also enhanced in response to nematode infection. Thus, the present study revealed high insecticidal potential and immunomodulatory effects of M. amsactae on G. mellonella that should be further explored on other insect pests as well.

Defense signaling pathways in resistance to plant viruses: Crosstalk and finger pointing

Resistance to infection by plant viruses involves proteins encoded by plant resistance (R) genes, viz., nucleotide-binding leucine-rich repeats (NLRs), immune receptors. These sensor NLRs are activated either directly or indirectly by viral protein effectors, in effector-triggered immunity, leading to induction of defense signaling pathways, resulting in the synthesis of numerous downstream plant effector molecules that inhibit different stages of the infection cycle, as well as the induction of cell death responses mediated by helper NLRs. Early events in this process involve recognition of the activation of the R gene response by various chaperones and the transport of these complexes to the sites of subsequent events. These events include activation of several kinase cascade pathways, and the syntheses of two master transcriptional regulators, EDS1 and NPR1, as well as the phytohormones salicylic acid, jasmonic acid, and ethylene. The phytohormones, which transit from a primed, resting states to active states, regulate the remainder of the defense signaling pathways, both directly and by crosstalk with each other. This regulation results in the turnover of various suppressors of downstream events and the synthesis of various transcription factors that cooperate and/or compete to induce or suppress transcription of either other regulatory proteins, or plant effector molecules. This network of interactions results in the production of defense effectors acting alone or together with cell death in the infected region, with or without the further activation of non-specific, long-distance resistance. Here, we review the current state of knowledge regarding these processes and the components of the local responses, their interactions, regulation, and crosstalk.

The impact of insect egg deposition on Pinus sylvestris transcriptomic and phytohormonal responses to larval herbivory

Plants can improve their resistance to feeding damage by insects if they have perceived insect egg deposition prior to larval feeding. Molecular analyses of these egg-mediated defence mechanisms have until now focused on angiosperm species. It is unknown how the transcriptome of a gymnosperm species responds to insect eggs and subsequent larval feeding. Scots pine (Pinus sylvestris L.) is known to improve its defences against larvae of the herbivorous sawfly Diprion pini L. if it has previously received sawfly eggs. Here, we analysed the transcriptomic and phytohormonal responses of Scots pine needles to D. pini eggs (E-pine), larval feeding (F-pine) and to both eggs and larval feeding (EF-pine). Pine showed strong transcriptomic responses to sawfly eggs and-as expected-to larval feeding. Many egg-responsive genes were also differentially expressed in response to feeding damage, and these genes play an important role in biological processes related to cell wall modification, cell death and jasmonic acid signalling. EF-pine showed fewer transcriptomic changes than F-pine, whereas EF-treated angiosperm species studied so far showed more transcriptional changes to the initial phase of larval feeding than only feeding-damaged F-angiosperms. However, as with responses of EF-angiosperms, EF-pine showed higher salicylic acid concentrations than F-pine. Based on the considerable overlap of the transcriptomes of E- and F-pine, we suggest that the weaker transcriptomic response of EF-pine than F-pine to larval feeding damage is compensated by the strong, egg-induced response, which might result in maintained pine defences against larval feeding.

Genome-wide identification of rubber tree pathogenesis-related 10 (PR-10) proteins with biological relevance to plant defense

Pathogenesis-related 10 (PR-10) is a group of small intracellular proteins that is one of 17 subclasses of pathogenesis-related proteins in plants. The PR-10 proteins have been studied extensively and are well-recognized for their contribution to host defense against phytopathogens in several plant species. Interestingly, the accumulation of PR-10 proteins in the rubber tree, one of the most economically important crops worldwide, after being infected by pathogenic organisms has only recently been reported. In this study, the homologous proteins of the PR-10 family were systemically identified from the recently available rubber tree genomes in the NCBI database. The sequence compositions, structural characteristics, protein physical properties, and phylogenetic relationships of identified PR-10 proteins in rubber trees support their classification into subgroups, which mainly consist of Pru ar 1-like major allergens and major latex-like (MLP) proteins. The rubber tree PR10-encoding genes were majorly clustered on chromosome 15. The potential roles of rubber tree PR-10 proteins are discussed based on previous reports. The homologous proteins in the PR-10 family were identified in the recent genomes of rubber trees and were shown to be crucial in host responses to biotic challenges. The genome-wide identification conducted here will accelerate the future study of rubber tree PR-10 proteins. A better understanding of these defense-related proteins may contribute to alternative ways of developing rubber tree clones with desirable traits in the future.

Genome-Wide Identification and Expression Analysis of Chitinase Genes in Watermelon under Abiotic Stimuli and Fusarium oxysporum Infection

Chitinases, which catalyze the hydrolysis of chitin, the primary components of fungal cell walls, play key roles in defense responses, symbiotic associations, plant growth, and stress tolerance. In this study, 23 chitinase genes were identified in watermelon (Citrullus lanatus [Thunb.]) and classified into five classes through homology search and phylogenetic analysis. The genes with similar exon-intron structures and conserved domains were clustered into the same class. The putative cis-elements involved in the responses to phytohormone, stress, and plant development were identified in their promoter regions. A tissue-specific expression analysis showed that the ClChi genes were primarily expressed in the roots (52.17%), leaves (26.09%), and flowers (34.78%). Moreover, qRT-PCR results indicate that ClChis play multifaceted roles in the interaction between plant/environment. More ClChi members were induced by Race 2 of Fusarium oxysporum f. sp. niveum, and eight genes were expressed at higher levels on the seventh day after inoculation with Races 1 and 2, suggesting that these genes play a key role in the resistance of watermelon to Fusarium wilt. Collectively, these results improve knowledge of the chitinase gene family in watermelon species and help to elucidate the roles played by chitinases in the responses of watermelon to various stresses.

Demography of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) reared on elicitor-treated tomato plants with an innovative comparison of projected population sizes and application of the multinomial theorem for population survival

BACKGROUND

Because of the considerable damage caused by tomato leafminer in tomato crops, the use of integrated methods is recommended. In this study, the effect of three different elicitors, methyl jasmonate, salicylic acid and ascorbic acid, on the life table parameters of Tuta absoluta was evaluated. A paired bootstrap test and different bootstrap percentiles were used to compare projected population sizes on specific dates. Survival probabilities were calculated by innovatively linking life tables and multinomial theorem.

RESULTS

Preadult duration and mortality significantly increased, and the net reproductive rate (R0 ), intrinsic rate of increase (r), and finite rate of increase (λ) significantly decreased in all elicitor treatments. The lowest fecundity (F = 71.89 eggs/female) was observed in the salicylic acid treatment, with an R0 value of 13.48 offspring/individual, r of 0.0932 d-1 , and λ of 1.0977 d-1 . The population projection revealed the stage structure of T. absoluta during population growth, which was significantly reduced by the elicitor treatments. The survival probability of bootstrap samples was significantly lowered, whereas the extinction probabilities increased in elicitor treatments compared with control when the survival criterion was set to two fertile pairs.

CONCLUSION

Our results demonstrated that the application of elicitors could reduce the risk of T. absoluta damage. Furthermore, population projection based on life tables is applicable to obtain the frequency distribution of the population size at different times. Combined application of life tables and multinomial theorem can be used to calculate the risk of pest emergence. © 2023 Society of Chemical Industry.

The expression of the NPR1-dependent defense response pathway genes in Persea americana (Mill.) following infection with Phytophthora cinnamomi

A plant's defense against pathogens involves an extensive set of phytohormone regulated defense signaling pathways. The salicylic acid (SA)-signaling pathway is one of the most well-studied in plant defense. The bulk of SA-related defense gene expression and the subsequent establishment of systemic acquired resistance (SAR) is dependent on the nonexpressor of pathogenesis-related genes 1 (NPR1). Therefore, understanding the NPR1 pathway and all its associations has the potential to provide valuable insights into defense against pathogens. The causal agent of Phytophthora root rot (PRR), Phytophthora cinnamomi, is of particular importance to the avocado (Persea americana) industry, which encounters considerable economic losses on account of this pathogen each year. Furthermore, P. cinnamomi is a hemibiotrophic pathogen, suggesting that the SA-signaling pathway plays an essential role in the initial defense response. Therefore, the NPR1 pathway which regulates downstream SA-induced gene expression would be instrumental in defense against P. cinnamomi. Thus, we identified 92 NPR1 pathway-associated orthologs from the P. americana West Indian pure accession genome and interrogated their expression following P. cinnamomi inoculation, using RNA-sequencing data. In total, 64 and 51 NPR1 pathway-associated genes were temporally regulated in the partially resistant (Dusa®) and susceptible (R0.12) P. americana rootstocks, respectively. Furthermore, 42 NPR1 pathway-associated genes were differentially regulated when comparing Dusa® to R0.12. Although this study suggests that SAR was established successfully in both rootstocks, the evidence presented indicated that Dusa® suppressed SA-signaling more effectively following the induction of SAR. Additionally, contrary to Dusa®, data from R0.12 suggested a substantial lack of SA- and NPR1-related defense gene expression during some of the earliest time-points following P. cinnamomi inoculation. This study represents the most comprehensive investigation of the SA-induced, NPR1-dependent pathway in P. americana to date. Lastly, this work provides novel insights into the likely mechanisms governing P. cinnamomi resistance in P. americana.

Characteristics and function of the pathogenesis-related protein 1 gene family in poplar

The pathogen-associated protein 1 (PR1) plays an important role in plant response to biotic and abiotic stresses. In this study, 17 PtPR1 genes were identified in Populus trichocarpa genome. The 17 PtPR1 genes were distributed on 7 chromosomes, and divided into A, B subfamilies by evolutionary tree analysis. RTqPCR analysis showed that the PtPR1 gene family showed different degrees of response to drought stress. PtPR1 genes showed changes in expression in response to fungal pathogen Septotinia populiperda or insect attacks (Nausinoe geometralis, Hyphantria cunea). Also, we found that subfamily B of PtPR1 may play an important role in response to biotic stress. We identified a new resistance gene PtPR1A. Overexpression of PtPR1A in Arabidopsis thaliana significantly enhanced the resistance to Pseudomonas syringae, while overexpression of PtPR1A in poplar significantly enhanced the resistance to S. populiperda. The present study investigates the expression pattern of the PtPR1 genes under biotic and abiotic stresses, and it found that the characteristics of the PtPR1 genes diverged, which provided a theoretical basis for the further study of the PtPR1 genes in the plant defense response.

Pathogen-induced m6A dynamics affect plant immunity

Posttranscriptional regulation of mRNA mediated by methylation at the N6 position of adenine (N6-methyladenosine [m6A]) has profound effects on transcriptome regulation in plants. Focused studies across eukaryotes offer glimpses into the processes governed by m6A throughout developmental and disease states. However, we lack an understanding of the dynamics and the regulatory potential of m6A during biotic stress in plants. Here, we provide a comprehensive look into the effects of m6A on both the short-term and long-term responses to pathogen signaling in Arabidopsis (Arabidopsis thaliana). We demonstrate that m6A-deficient plants are more resistant to bacterial and fungal pathogen infections and have altered immune responses. Furthermore, m6A deposition is specifically coordinated on transcripts involved in defense and immunity prior to and proceeding the pathogen signal flagellin. Consequently, the dynamic modulation of m6A on specific stress-responsive transcripts is correlated with changes in abundance and cleavage of these transcripts. Overall, we show that the m6A methylome is regulated prior to and during simulated and active pathogen stress and functions in the coordination and balancing of normal growth and pathogen responses.

Transcriptomic and metabolic profiling of watermelon uncovers the role of salicylic acid and flavonoids in the resistance to cucumber green mottle mosaic virus

Understanding the mechanisms underlying plant resistance to virus infections is crucial for viral disease management in agriculture. However, the defense mechanism of watermelon (Citrullus lanatus) against cucumber green mottle mosaic virus (CGMMV) infection remains largely unknown. In this study, we performed transcriptomic, metabolomic, and phytohormone analyses of a CGMMV susceptible watermelon cultivar 'Zhengkang No.2' ('ZK') and a CGMMV resistant wild watermelon accession PI 220778 (PI) to identify the key regulatory genes, metabolites, and phytohormones responsible for CGMMV resistance. We then tested several phytohormones and metabolites for their roles in watermelon CGMMV resistance via foliar application, followed by CGMMV inoculation. Several phenylpropanoid metabolism-associated genes and metabolites, especially those involved in the flavonoid biosynthesis pathway, were found to be significantly enriched in the CGMMV-infected PI plants compared with the CGMMV-infected 'ZK' plants. We also identified a gene encoding UDP-glycosyltransferase (UGT) that is involved in kaempferol-3-O-sophoroside biosynthesis and controls disease resistance, as well as plant height. Additionally, salicylic acid (SA) biogenesis increased in the CGMMV-infected 'ZK' plants, resulting in the activation of a downstream signaling cascade. SA levels in the tested watermelon plants correlated with that of total flavonoids, and SA pre-treatment up-regulated the expression of flavonoid biosynthesis genes, thus increasing the total flavonoid content. Furthermore, application of exogenous SA or flavonoids extracted from watermelon leaves suppressed CGMMV infection. In summary, our study demonstrates the role of SA-induced flavonoid biosynthesis in plant development and CGMMV resistance, which could be used to breed for CGMMV resistance in watermelon.

Identification and characterization of novel sesquiterpene synthases TPS9 and TPS12 from Aquilaria sinensis

Sesquiterpenes are characteristic components and important quality criterions for agarwood. Although sesquiterpenes are well-known to be biosynthesized by sesquiterpene synthases (TPSs), to date, only a few TPS genes involved in agarwood formation have been reported. Here, two new TPS genes, namely, TPS9 and TPS12, were isolated from Aquilaria sinensis (Lour.) Gilg, and their functions were examined in Escherichia coli BL21(DE3), with farnesyl pyrophosphate (FPP) and geranyl pyrophosphate (GPP) as the substrate of the corresponding enzyme activities. They were both identified as a multiproduct enzymes. After incubation with FPP, TPS9 liberated β-farnesene and cis-sesquisabinene hydrate as main products, with cedrol and another unidentified sesquiterpene as minor products. TPS12 catalyzes the formation of β-farnesene, nerolidol, γ-eudesmol, and hinesol. After incubation with GPP, TPS9 generated citronellol and geraniol as main products, with seven minor products. TPS12 converted GPP into four monoterpenes, with citral as the main product, and three minor products. Both TPS9 and TPS12 showed much higher expression in the two major tissues emitting floral volatiles: flowers and agarwood. Further, RT-PCR analysis showed TPS9 and TPS12 are typical genes mainly expressed during later stages of stress response, which is better known than that of chromone derivatives. This study will advance our understanding of agarwood formation and provide a solid theoretical foundation for clarifying its mechanism in A. sinensis.

A snapshot of the transcriptome of Medicago truncatula (Fabales: Fabaceae) shoots and roots in response to an arbuscular mycorrhizal fungus and the pea aphid (Acyrthosiphon pisum) (Hemiptera: Aphididae)

Plants simultaneously interact with belowground symbionts such as arbuscular mycorrhizal (AM) fungi and aboveground antagonists such as aphids. Generally, plants gain access to valuable resources including nutrients and water through the AM symbiosis and are more resistant to pests. Nevertheless, aphids' performance improves on mycorrhizal plants, and it remains unclear whether a more nutritious food source and/or attenuated defenses are the contributing factors. This study examined the shoot and root transcriptome of barrel medic (Medicago truncatula Gaertn.) plants highly colonized by the AM fungus Rhizophagus irregularis (Blaszk., Wubet, Renker, and Buscot) C. Walker and A. Schüßler (Glomerales: Glomeraceae) and exposed to 7 days of mixed age pea aphid (Acyrthosiphon pisum (Harris)) herbivory. The RNA-seq samples chosen for this study showed that aphids were heavier when fed mycorrhizal plants compared to nonmycorrhizal plants. We hypothesized that (i) insect-related plant defense pathways will be downregulated in shoots of mycorrhizal plants with aphids compared to nonmycorrhizal plants with aphids; (ii) pathways involved in nutrient acquisition, carbohydrate-related and amino acid transport will be upregulated in shoots of mycorrhizal plants with aphids compared to nonmycorrhizal plants with aphids; and (iii) roots of mycorrhizal plants with aphids will exhibit mycorrhiza-induced resistance. The transcriptome data revealed that the gene repertoire related to defenses, nutrient transport, and carbohydrates differs between nonmycorrhizal and mycorrhizal plants with aphids, which could explain the weight gain in aphids. We also identified novel candidate genes that are differentially expressed in nonmycorrhizal plants with aphids, thus setting the stage for future functional studies.

Variation in the Outcome of Plant-Mediated Pathogen Interactions in Potato: Effects of Initial Infections on Conspecific vs. Heterospecific Subsequent Infections

Plants are often attacked sequentially by multiple enemies. Pathogen sequential co-infections can lead to indirect interactions mediated by plant induced responses whose outcome is contingent on differences in the magnitude and type of plant induced defences elicited by different species or guilds. To date, however, most studies have tested unidirectional effects of one pathogen on another, not discerning between conspecific vs. heterospecific infections, and often not measuring plant induced responses underlying such outcomes. To address this, we conducted a greenhouse experiment testing for the impact of initial infection by two leaf pathogens (Alternaria solani and Phytophthora infestans) on subsequent infection by each of these pathogens on potato (Solanum tuberosum) plants, and also measured induced plant defences (phenolic compounds) to inform on interaction outcomes. We found contrasting results depending on the identity of the initially infecting pathogen. Specifically, initial infection by A. solani drove induced resistance (lower necrosis) by subsequently infecting A. solani (conspecific induced resistance) but had no effect on subsequent infection by P. infestans. In contrast, initial infection by P. infestans drove induced resistance to subsequent infection by both conspecifics and A. solani. Patterns of plant induced defences correlated with (and potentially explained) induced resistance to conspecific but not heterospecific (e.g., in the case of P. infestans) subsequent infection. Overall, these results further our understanding of plant-mediated pathogen interactions by showing that plant-mediated interactions between pathogen species can be asymmetrical and in some cases not reciprocal, that pathogen species can vary in the importance of conspecific vs. heterospecific effects, and shed mechanistic insight into the role of plant induced responses driving such interactions.

A wound inducible chalcone synthase gene from Dysoxylum gotadhora (DbCHS) regulates flavonoid biosynthesis

Chalcone synthase (CHS) is a type III polyketide synthase and a key enzyme of the phenylpropanoid pathway that generates precursors for flavonoid biosynthesis. The tree species D. gotadhora is known for having an abundance of rohitukine, which has anti-inflammatory and immune-modulating effects. In this study, we used the leaves of D. gotadhora to clone CHS gene (DbCHS). The 1188-bp open reading frame (ORF) was part of the 1373-bp full-length DbCHS clone. Compared to other parts of the plant, DbCHS is expressed more in the leaves and fruits. This is linked to anti-microbial action against a panel of microbes in these tissues. The leaves and seeds extracts inhibit Bacillus subtilis, Streptococcus pyogenes, Bacillus cereus, and Candida albicans. When a plant is hurt, it leaves its tissues open to attack by microbes. To protect themselves, plants often make chemicals that kill microbes. We found that wounding had a big effect on the production of DbCHS. Based on these tests and the results of phylogenetic analysis and molecular docking, we believe that DbCHS is a wound-inducible enzyme that is needed to make flavonoids, which may give the plant antimicrobial properties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01344-2.

GDSL Esterase/Lipase GELP1 Involved in the Defense of Apple Leaves against Colletotrichum gloeosporioides Infection

GDSL esterases/lipases are a subclass of lipolytic enzymes that play critical roles in plant growth and development, stress response, and pathogen defense. However, the GDSL esterase/lipase genes involved in the pathogen response of apple remain to be identified and characterized. Thus, in this study, we aimed to analyze the phenotypic difference between the resistant variety, Fuji, and susceptible variety, Gala, during infection with C. gloeosporioides, screen for anti-disease-associated proteins in Fuji leaves, and elucidate the underlying mechanisms. The results showed that GDSL esterase/lipase protein GELP1 contributed to C. gloeosporioides infection defense in apple. During C. gloeosporioides infection, GELP1 expression was significantly upregulated in Fuji. Fuji leaves exhibited a highly resistant phenotype compared with Gala leaves. The formation of infection hyphae of C. gloeosporioides was inhibited in Fuji. Moreover, recombinant His:GELP1 protein suppressed hyphal formation during infection in vitro. Transient expression in Nicotiana benthamiana showed that GELP1-eGFP localized to the endoplasmic reticulum and chloroplasts. GELP1 overexpression in GL-3 plants increased resistance to C. gloeosporioides. MdWRKY15 expression was upregulated in the transgenic lines. Notably, GELP1 transcript levels were elevated in GL-3 after salicylic acid treatment. These results suggest that GELP1 increases apple resistance to C. gloeosporioides by indirectly regulating salicylic acid biosynthesis.

An unexpected role for tomato threonine deaminase 2 in host defense against bacterial infection

The hormones salicylic acid (SA) and jasmonic acid (JA) often act antagonistically in controlling plant defense pathways in response to hemibiotrophs/biotrophs (hemi/biotroph) and herbivores/necrotrophs, respectively. Threonine deaminase (TD) converts threonine to α-ketobutyrate and ammonia as the committed step in isoleucine (Ile) biosynthesis and contributes to JA responses by producing the Ile needed to make the bioactive JA-Ile conjugate. Tomato (Solanum lycopersicum) plants have two TD genes: TD1 and TD2. A defensive role for TD2 against herbivores has been characterized in relation to JA-Ile production. However, it remains unknown whether TD2 is also involved in host defense against bacterial hemi/biotrophic and necrotrophic pathogens. Here, we show that in response to the bacterial pathogen-associated molecular pattern (PAMP) flagellin flg22 peptide, an activator of SA-based defense responses, TD2 activity is compromised, possibly through carboxy-terminal cleavage. TD2 knockdown (KD) plants showed increased resistance to the hemibiotrophic bacterial pathogen Pseudomonas syringae but were more susceptible to the necrotrophic fungal pathogen Botrytis cinerea, suggesting TD2 plays opposite roles in response to hemibiotrophic and necrotrophic pathogens. This TD2 KD plant differential response to different pathogens is consistent with SA- and JA-regulated defense gene expression. flg22-treated TD2 KD plants showed high expression levels of SA-responsive genes, whereas TD2 KD plants treated with the fungal PAMP chitin showed low expression levels of JA-responsive genes. This study indicates TD2 acts negatively in defense against hemibiotrophs and positively against necrotrophs and provides insight into a new TD2 function in the elaborate crosstalk between SA and JA signaling induced by pathogen infection.

Rhizobacterial Colonization and Management of Bacterial Speck Pathogen in Tomato by Pseudomonas spp

Plants and soil microorganisms interact at every stage of growth. Pseudomonas spp. are highly regarded for their ability to increase crop production and protection from diseases. The aim of this study is to understand the mechanisms of the rhizobacterial colonization of tomato roots via chemotaxis assay and the activation of tomato resistance against the pathogenic bacterium, Pseudomonas syringae pv. tomato DC3000 (Pst). The capillary assay was used to evaluate the chemotaxis response of PGPRs (plant growth-promoting rhizobacteria). The activities of defense enzymes and the expressions of PR (pathogenesis-related) genes were measured using real-time qPCR. Chemotactic responses to malic and citric acids (the most important root exudates found in different plant species) at low concentrations varied substantially among the rhizobacterial isolates (63 species). Beneficial isolates including Pseudomonas resinovorans A5, P. vranovensis A30, P. resinovorans A28, P. umsongensis O26, P. stutzeri N42, and P. putida T15 reacted well to different concentrations of root exudates. P. putida T15 demonstrated the most potent anti-Pst activity. At three and six days after inoculation, the greatest levels of polyphenol oxidase and peroxidase activity were reported in the A5 and T15 groups. In tomato, transcript levels of four PR (pathogenesis-related) genes were elevated by rhizobacterial treatments. PGPR isolates alone or in combination with BABA (β-amino butyric acid) up-regulated the transcriptions of PR1, PR2, LOX, and PAL genes. Treatments with N42 and T15 resulted in the greatest improvements in tomato growth and yield traits. In conclusion, the results explain the mechanisms of rhizobacterial colonization for the improved management of Pst. Rhizobacterial isolates play a role in tomato's resistance to Pst via salicylic acid and jasmonic acid pathways.

NbMLP43 Ubiquitination and Proteasomal Degradation via the Light Responsive Factor NbBBX24 to Promote Viral Infection

The ubiquitin-proteasome system (UPS) plays an important role in virus-host interactions. However, the mechanism by which the UPS is involved in innate immunity remains unclear. In this study, we identified a novel major latex protein-like protein 43 (NbMLP43) that conferred resistance to Nicotiana benthamiana against potato virus Y (PVY) infection. PVY infection strongly induced NbMLP43 transcription but decreased NbMLP43 at the protein level. We verified that B-box zinc finger protein 24 (NbBBX24) interacted directly with NbMLP43 and that NbBBX24, a light responsive factor, acted as an essential intermediate component targeting NbMLP43 for its ubiquitination and degradation via the UPS. PVY, tobacco mosaic virus, (TMV) and cucumber mosaic virus (CMV) infections could promote NbMLP43 ubiquitination and proteasomal degradation to enhance viral infection. Ubiquitination occurred at lysine 38 (K38) within NbMLP43, and non-ubiquitinated NbMLP43(K38R) conferred stronger resistance to RNA viruses. Overall, our results indicate that the novel NbMLP43 protein is a target of the UPS in the competition between defense and viral anti-defense and enriches existing theoretical studies on the use of UPS by viruses to promote infection.

GmWAK1, Novel Wall-Associated Protein Kinase, Positively Regulates Response of Soybean to Phytophthora sojae Infection

Phytophthora root rot is a destructive soybean disease worldwide, which is caused by the oomycete pathogen Phytophthora sojae (P. sojae). Wall-associated protein kinase (WAK) genes, a family of the receptor-like protein kinase (RLK) genes, play important roles in the plant signaling pathways that regulate stress responses and pathogen resistance. In our study, we found a putative Glycine max wall-associated protein kinase, GmWAK1, which we identified by soybean GmLHP1 RNA-sequencing. The expression of GmWAK1 was significantly increased by P. sojae and salicylic acid (SA). Overexpression of GmWAK1 in soybean significantly improved resistance to P. sojae, and the levels of phenylalanine ammonia-lyase (PAL), SA, and SA-biosynthesis-related genes were markedly higher than in the wild-type (WT) soybean. The activities of enzymatic superoxide dismutase (SOD) and peroxidase (POD) antioxidants in GmWAK1-overexpressing (OE) plants were significantly higher than those in in WT plants treated with P. sojae; reactive oxygen species (ROS) and hydrogen peroxide (H₂O₂) accumulation was considerably lower in GmWAK1-OE after P. sojae infection. GmWAK1 interacted with annexin-like protein RJ, GmANNRJ4, which improved resistance to P. sojae and increased intracellular free-calcium accumulation. In GmANNRJ4-OE transgenic soybean, the calmodulin-dependent kinase gene GmMPK6 and several pathogenesis-related (PR) genes were constitutively activated. Collectively, these results indicated that GmWAK1 interacts with GmANNRJ4, and GmWAK1 plays a positive role in soybean resistance to P. sojae via a process that might be dependent on SA and involved in alleviating damage caused by oxidative stress.

Overexpression of a Cinnamyl Alcohol Dehydrogenase-Coding Gene, GsCAD1, from Wild Soybean Enhances Resistance to Soybean Mosaic Virus

Soybean mosaic virus (SMV) is the most prevalent soybean viral disease in the world. As a critical enzyme in the secondary metabolism of plants, especially in lignin synthesis, cinnamyl alcohol dehydrogenase (CAD) is widely involved in plant growth and development, and in defense against pathogen infestation. Here, we performed RNAseq-based transcriptome analyses of a highly SMV-resistant accession (BYO-15) of wild soybean (Glycine soja) and a SMV-susceptible soybean cultivar (Williams 82), also sequenced together with a resistant plant and a susceptible plant of their hybrid descendants at the F3 generation at 7 and 14 days post-inoculation with SMV. We found that the expression of GsCAD1 (from G. soja) was significantly up-regulated in the wild soybean and the resistant F3 plant, while the GmCAD1 from the cultivated soybean (G. max) did not show a significant and persistent induction in the soybean cultivar and the susceptible F3 plant, suggesting that GsCAD1 might play an important role in SMV resistance. We cloned GsCAD1 and overexpressed it in the SMV-susceptible cultivar Williams 82, and we found that two independent GsCAD1-overexpression (OE) lines showed significantly enhanced SMV resistance compared with the non-transformed wild-type (WT) control. Intriguingly, the lignin contents in both OE lines were higher than the WT control. Further liquid chromatography (HPLC) analysis showed that the contents of salicylic acid (SA) were significantly more improved in the OE lines than that of the wild-type (WT), coinciding with the up-regulated expression of an SA marker gene. Finally, we observed that GsCAD1-overexpression affected the accumulation of SMV in leaves. Collectively, our results suggest that GsCAD1 enhances resistance to SMV in soybeans, most likely by affecting the contents of lignin and SA.

Loss-of-function of NITROGEN LIMITATION ADAPTATION confers disease resistance in Arabidopsis by modulating hormone signaling and camalexin content

Phosphorus is an important macronutrient required for plant growth and development. It is absorbed by the roots in the form of inorganic phosphate (Pi). Under Pi limiting conditions, plants activate the Phosphate Starvation Response (PSR) system to enhance Pi acquisition. The NITROGEN LIMITATION ADAPTION (NLA) gene is a component of the Arabidopsis PSR, and its expression is post-transcriptionally regulated by miR827. We show that loss-of-function of NLA and MIR827 overexpression increases Pi level and enhances resistance to infection by the fungal pathogen Plectosphaerella cucumerina in Arabidopsis. Upon pathogen infection, high Pi plants (e.g. nla plants and wild type plants grown under high Pi supply) showed enhanced callose deposition. High Pi plants also exhibited superinduction of camalexin biosynthesis genes which is consistent with increased levels of camalexin during pathogen infection. Pathogen infection and treatment with fungal elicitors, triggered up-regulation of MIR827 and down-regulation of NLA expression. Under non-infection conditions, the nla plants showed increased levels of SA and JA compared with wild type plants, their levels further increasing upon pathogen infection. Overall, the outcomes of this study suggest that NLA plays a role in Arabidopsis immunity, while supporting convergence between Pi signaling and immune signaling in Arabidopsis.

Interference between ER stress-related bZIP-type and jasmonate-inducible bHLH-type transcription factors in the regulation of triterpene saponin biosynthesis in Medicago truncatula

Triterpene saponins (TS) are a structurally diverse group of metabolites that are widely distributed in plants. They primarily serve as defense compounds and their production is often triggered by biotic stresses through signaling cascades that are modulated by phytohormones such as the jasmonates (JA). Two JA-modulated basic helix-loop-helix (bHLH) transcription factors (TFs), triterpene saponin biosynthesis activating regulator 1 (TSAR1) and TSAR2, have previously been identified as direct activators of TS biosynthesis in the model legume Medicago truncatula. Here, we report on the involvement of the core endoplasmic reticulum (ER) stress-related basic leucine zipper (bZIP) TFs bZIP17 and bZIP60 in the regulation of TS biosynthesis. Expression and processing of M. truncatula bZIP17 and bZIP60 proteins were altered in roots with perturbed TS biosynthesis or treated with JA. Accordingly, such roots displayed an altered ER network structure. M. truncatula bZIP17 and bZIP60 proteins were shown to localize in the nucleus and appeared to be capable of interfering with the TSAR-mediated transactivation of TS biosynthesis genes. Furthermore, interference between ER stress-related bZIP and JA-modulated bHLH TFs in the regulation of JA-dependent terpene biosynthetic pathways may be widespread in the plant kingdom, as we demonstrate that it also occurs in the regulation of monoterpene indole alkaloid biosynthesis in the medicinal plant Catharanthus roseus.

Identification of genes controlling compatible and incompatible reactions of pearl millet (Pennisetum glaucum) against blast (Magnaporthe grisea) pathogen through RNA-Seq

Blast [Magnaporthe grisea (Herbert) Barr] is an economically important disease in Asian pearl millet production ecologies. The recurrent occurrence of blast in the past one decade has caused enormous strain on grain and forage production. Identification of resistance genes is an important step to develop durable varieties. The present study is the first attempt to use RNA-Seq to investigate the transcript dynamics in a pearl millet inbred ICMB 93333, which had a unique differential reaction to two isolates-Pg 45 (avirulent) and Pg 174 (virulent) of M. grisea. The inbred was inoculated by both isolates and samples taken at six different time intervals for genome-wide RNA-Seq experiment. The transcriptome results revealed the differential expression of more than 2,300 genes. The time-specific comparison showed activation or repression of specific genes in various pathways. Genes and transcriptions factors related to pathogenesis-related proteins, reactive oxygen species generating and its scavenging genes, cell wall defense, primary and secondary metabolic pathways, and signaling pathways were identified by comparing the host-plant compatible and incompatible interactions. The genes identified from this experiment could be useful to understand the host-plant resistance and design novel strategies to manage blast disease in pearl millet.

Lack of antagonism between salicylic acid and jasmonate signalling pathways in poplar

Salicylic acid (SA) and jasmonic acid (JA) often play distinct roles in plant defence against pathogens. Research from Arabidopsis thaliana has established that SA- and JA-mediated defences are more effective against biotrophs and necrotrophs, respectively. These two hormones often interact antagonistically in response to particular attackers, with the induction of one leading to suppression of the other. Here, we report a contrasting pattern in the woody perennial Populus: positive SA-JA interplay. Using genetically engineered high SA lines of black poplar and wild-type lines after exogenous hormone application, we quantified SA and JA metabolites, signalling gene transcripts, antifungal flavonoids and resistance to rust (Melampsora larici-populina). Salicylic acid and JA metabolites were induced concurrently upon rust infection in poplar genotypes with varying resistance levels. Analysis of SA-hyperaccumulating transgenic poplar lines showed increased jasmonate levels, elevated flavonoid content and enhanced rust resistance, but no discernible reduction in growth. Exogenous application of either SA or JA triggered the accumulation of the other hormone. Expression of pathogenesis-related (PR) genes, frequently used as markers for SA signalling, was not correlated with SA content, but rather activated in proportion to pathogen infection. We conclude that SA and JA pathways interact positively in poplar resulting in the accumulation of flavonoid phytoalexins.

Oviposition by a Specialist Herbivore Increases Susceptibility of Canola to Herbivory by a Generalist Herbivore

Oviposition by specialist herbivores can alter the suitability of the host plant to subsequent infestation by other herbivores. In this study, we tested the effect of previous oviposition on canola, Brassica napus L., by a Brassica specialist, the diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), on subsequent herbivory by the generalist feeder, the bertha armyworm (BAW), Mamestra configurata Walker (Lepidoptera: Noctuidae). The effect of DBM oviposition on subsequent BAW oviposition and larval feeding was tested in no-choice and choice experiments. Oviposition of BAW was not altered by DBM eggs on canola plants, however, BAW had increased larval feeding on plants with DBM eggs. These results suggest that oviposition by a specialist herbivore increased the susceptibility of the host plant to generalist herbivory. In a preliminary experiment, salicylic acid, jasmonic acid, and its conjugates were not altered by DBM oviposition on canola, however, further experimentation is needed to determine if oviposition affects expression of plant defense pathways and other plant traits.

Molecular evolution and functional characterization of chitinase gene family in Populus trichocarpa

Chitinases, the chitin-degrading enzymes, have been shown to play important role in defense against the chitin-containing fungal pathogens. In this study, we identified 48 chitinase-coding genes from the woody model plant Populus trichocarpa. Based on phylogenetic analysis, the Populus chitinases were classified into seven groups. Different gene structures and protein domain architectures were found among the seven Populus chitinase groups. Selection pressure analysis indicated that all the seven groups are under purifying selection. Phylogenetic analysis combined with chromosome location analysis showed that Populus chitinase gene family mainly expanded through tandem duplication. The Populus chitinase gene family underwent marked expression divergence and is inducibly expressed in response to treatments, such as chitosan, chitin, salicylic acid and methyl jasmonate. Protein enzymatic activity analysis showed that Populus chitinases had activity towards both chitin and chitosan. By integrating sequence characteristic, phylogenetic, selection pressure, gene expression and protein activity analysis, this study shed light on the evolution and function of chitinase family in poplar.

Large-Scale Protein and Phosphoprotein Profiling to Explore Potato Resistance Mechanisms to Spongospora subterranea Infection

Potato is one of the most important food crops for human consumption. The soilborne pathogen Spongospora subterranea infects potato roots and tubers, resulting in considerable economic losses from diminished tuber yields and quality. A comprehensive understanding of how potato plants respond to S. subterranea infection is essential for the development of pathogen-resistant crops. Here, we employed label-free proteomics and phosphoproteomics to quantify systemically expressed protein-level responses to S. subterranea root infection in potato foliage of the susceptible and resistant potato cultivars. A total of 2,669 proteins and 1,498 phosphoproteins were quantified in the leaf samples of the different treatment groups. Following statistical analysis of the proteomic data, we identified oxidoreductase activity, electron transfer, and photosynthesis as significant processes that differentially changed upon root infection specifically in the resistant cultivar and not in the susceptible cultivar. The phosphoproteomics results indicated increased activity of signal transduction and defense response functions in the resistant cultivar. In contrast, the majority of increased phosphoproteins in the susceptible cultivar were related to transporter activity and sub-cellular localization. This study provides new insight into the molecular mechanisms and systemic signals involved in potato resistance to S. subterranea infection and has identified new roles for protein phosphorylation in the regulation of potato immune response.

Comparative Transcriptome Analysis of Onion in Response to Infection by Alternaria porri (Ellis) Cifferi

Purple blotch (PB) is one of the most destructive foliar diseases of onion and other alliums, caused by a necrotrophic fungal pathogen Alternaria porri. There are no reports on the molecular response of onion to PB infection. To elucidate the response of onion to A. porri infection, we consequently carried out an RNAseq analysis of the resistant (Arka Kalyan; AK) and susceptible (Agrifound rose; AFR) genotype after an artificial infection. Through differential expression analyses between control and pathogen-treated plants, we identified 8,064 upregulated and 248 downregulated genes in AFR, while 832 upregulated and 564 downregulated genes were identified in AK. A further significant reprogramming in the gene expression profile was also demonstrated by a functional annotation analysis. Gene ontology (GO) terms, which are particularly involved in defense responses and signaling, are overrepresented in current analyses such as "oxidoreductase activity," "chitin catabolic processes," and "defense response." Several key plant defense genes were differentially expressed on A. porri infection, which includes pathogenesis-related (PR) proteins, receptor-like kinases, phytohormone signaling, cell-wall integrity, cytochrome P450 monooxygenases, and transcription factors. Some of the genes were exclusively overexpressed in resistant genotype, namely, GABA transporter1, ankyrin repeat domain-containing protein, xyloglucan endotransglucosylase/hydrolase, and PR-5 (thaumatin-like). Antioxidant enzyme activities were observed to be increased after infection in both genotypes but higher activity was found in the resistant genotype, AK. This is the first report of transcriptome profiling in onion in response to PB infection and will serve as a resource for future studies to elucidate the molecular mechanism of onion-A. porri interaction and to improve PB resistance in onions.

The necrotroph Botrytis cinerea promotes disease development in Panax ginseng by manipulating plant defense signals and antifungal metabolites degradation

Background

Panax ginseng Meyer is one of the most valuable medicinal plants which is enriched in anti-microbe secondary metabolites and widely used in traditional medicine. Botrytis cinerea is a necrotrophic fungus that causes gray mold disease in a broad range of hosts. B. cinerea could overcome the ginseng defense and cause serious leaf and root diseases with unknown mechanism.

Methods

We conducted simultaneous transcriptomic and metabolomic analysis of the host to investigate the defense response of ginseng affected by B. cinerea. The gene deletion and replacement were then performed to study the pathogenic gene in B. cinerea during ginseng - fungi interaction.

Results

Upon B. cinerea infection, ginseng defense responses were switched from the activation to repression, thus the expression of many defense genes decreased and the biosynthesis of antifungal metabolites were reduced. Particularly, ginseng metabolites like kaempferol, quercetin and luteolin which could inhibit fungi growth were decreased after B. cinerea infection. B. cinerea quercetin dioxygenase (Qdo) involved in catalyzing flavonoids degradation and △BcQdo mutants showed increased substrates accumulation and reduced disease development.

Conclusion

This work indicates the flavonoids play a role in ginseng defense and BcQdo involves in B. cinerea virulence towards the P. ginseng. B. cinerea promotes disease development in ginseng by suppressing of defense related genes expression and reduction of antifungal metabolites biosynthesis.

AP2/ERF Transcription Factor NbERF-IX-33 Is Involved in the Regulation of Phytoalexin Production for the Resistance of Nicotiana benthamiana to Phytophthora infestans

Plants recognize molecular patterns unique to a certain group of microbes to induce effective resistance mechanisms. Elicitins are secretory proteins produced by plant pathogenic oomycete genera including Phytophthora and Pythium. Treatment of INF1 (an elicitin produced by P. infestans) induces a series of defense responses in Nicotiana species, including reactive oxygen species (ROS) production, transient induction of ethylene production, hypersensitive cell death and accumulation of the sesquiterpenoid phytoalexin capsidiol. In this study, we analyzed the expression profiles of N. benthamiana genes after INF1 treatment by RNAseq analysis. Based on their expression patterns, N. benthamiana genes were categorized into 20 clusters and 4,761 (8.3%) out of 57,140 genes were assigned to the clusters for INF1-induced genes. All genes encoding enzymes dedicated to capsidiol production, 5-epi-aristolochene (EA) synthase (NbEAS, 10 copies) and EA dehydrogenase (NbEAH, 6 copies), and some genes for ethylene production, such as 1-aminocyclopropane 1-carboxylate (ACC) synthase (NbACS) and ACC oxidase (NbACO), were significantly upregulated by INF1 treatment. Analysis of NbEAS1 and NbEAS4 promoters revealed that AGACGCC (GCC box-like motif) is the essential cis-element required for INF1-induced expression of NbEAS genes. Given that the GCC box is known to be targeted by ERF (ethylene-responsive factor) transcription factors, we created a complete list of N. benthamiana genes encoding AP2/ERF family transcription factors, and identified 45 out of 337 AP2/ERF genes in the clusters for INF1-induced genes. Among INF1-induced NbERF genes, silencing of NbERF-IX-33 compromised resistance against P. infestans and INF1-induced production of capsidiol. Recombinant NbERF-IX-33 protein can bind to the promoter sequence of NbEAS4, suggesting that NbERF-IX-33 is a transcription factor directly regulating the expression of genes for phytoalexin production.

Defence Responses Associated with Elicitor-Induced, Cultivar-Associated Resistance to Latania Scale in Kiwifruit

Latania scale insect is a pest of global significance affecting kiwifruit. The sessile insect (life stage: settled crawler-mature adult) is covered with a waxy cap that protects it from topical pesticides, so increasingly, a selection of resistant cultivars and application of elicitors are being used in pest control. Thus far, the application of a salicylic acid (SA) phytohormone pathway elicitor, acibenzolar-S-methyl (ASM), has been shown to reduce insect development (as indicated by cap size) on one kiwifruit cultivar ('Hayward'). To investigate how cultivar-associated resistance is affected by the ability to respond to different elicitors, we measured phytohormones (by LCMS) and gene expression (by qPCR and NanoString) on latania scale-tolerant 'Hort16A' and susceptible 'Hayward' kiwifruit over two seasons. Potted plants in the presence/absence of settled latania scales were treated with ASM (0.2 g/L) or methyl jasmonate (MeJA, 0.05% v/v), representing elicitors of the SA and JA signalling pathways, respectively. 'Hort16A' cultivar resistance to latania scale was associated with elevated expression of SA and SA-related defence genes (PR1 and two PR2 family genes) in the ASM treatment. MeJA treatments did not significantly affect insect development in 'Hayward' (latania scale did not survive on 'Hort16A') and did not correlate with phytohormone and gene expression measurements in either cultivar. 'Hayward' had greater concentrations than 'Hort16A' of inert storage forms of both SA and JA across all treatments. This information contributes to the selection of tolerant cultivars and the effective use of elicitors for control of latania scale in kiwifruit.

Gibberellic Acid and Jasmonic Acid Improve Salt Tolerance in Summer Squash by Modulating Some Physiological Parameters Symptomatic for Oxidative Stress and Mineral Nutrition

Gibberellic acid (GA) and jasmonic acid (JA) are considered to be endogenous regulators that play a vital role in regulating plant responses to stress conditions. This study investigated the ameliorative role of GA, JA, and the GA + JA mixture in mitigating the detrimental effect of salinity on the summer squash plant. In order to explore the physiological mechanisms of salt stress alleviation carried out by exogenous GA and JA, seed priming with 1.5 mM GA, 0.005 mM JA, and their mixture was performed; then the germinated summer squash seedlings were exposed to 50 mM NaCl. The results showed that a 50 mM NaCl treatment significantly reduced shoot and root fresh and dry weight, water content (%), the concentration of carotenoid (Car), nucleic acids, K+, and Mg++, the K+/Na+ ratio, and the activity of catalase (CAT) and ascorbate peroxidase (APX), while it increased the concentration of proline, thiobarbituric acid reactive substances (TBARS), Na+, and Cl- in summer squash plants, when compared with the control. However, seed priming with GA, JA and the GA + JA mixture significantly improved summer squash salt tolerance by reducing the concentration of Na+ and Cl-, TBARS, and the Chl a/b ratio and by increasing the activity of superoxide dismutase, CAT, and APX, the quantities of K+ and Mg++, the K+/Na+ ratio, and the quantities of RNA, DNA, chlorophyll b, and Car, which, in turn, ameliorated the growth of salinized plants. These findings suggest that GA and JA are able to efficiently defend summer squash plants from salinity destruction by adjusting nutrient uptake and increasing the activity of antioxidant enzymes in order to decrease reactive oxygen species accumulation due to salinity stress; these findings offer a practical intervention for summer squash cultivation in salt-affected soils. Synergistic effects of the GA and JA combination were not clearly observed, and JA alleviated most of the studied traits associated with salinity stress induced in summer squash more efficiently than GA or the GA + JA mixture.

[Ribosomal profiling as a tool for studying translation in plants: main results, problems and future prospects]

The expression of eukaryotic genes can be regulated at several stages, including the translation of mRNA. It is known that the structure of mRNA can affect both the efficiency of interaction with the translation apparatus in general and the choice of translation initiation sites. To study the translated fraction of the transcriptome, experimental methods of analysis were developed, the most informative of which is ribosomal profiling (RP, Ribo-seq). Originally developed for use in yeast systems, this method has been adapted for research in translation mechanisms in many plant species. This technology includes the isolation of the polysomal fraction and high-performance sequencing of a pool of mRNA fragments associated with ribosomes. Comparing the results of transcript coverage with reads obtained using the ribosome profiling with the transcriptional efficiency of genes allows the translation efficiency to be evaluated for each transcript. The exact positions of ribosomes determined on mRNA sequences allow determining the translation of open reading frames and switching between the translation of several reading frames - a phenomenon in which two or more overlapping frames are read from one mRNA and different proteins are synthesized. The advantage of this method is that it provides quantitative estimates of ribosome coverage of mRNA and can detect relatively rare translation events. Using this technology, it was possible to identify and classify plant genes by the type of regulation of their expression at the transcription, translation, or both levels. Features of the mRNA structure that affect translation levels have been revealed: the formation of G2 quadruplexes and the presence of specific motifs in the 5'-UTR region, GC content, the presence of alternative translation starts, and the influence of uORFs on the translation of downstream mORFs. In this review, we briefly reviewed the RP methodology and the prospects for its application to study the structural and functional organization and regulation of plant gene expression.

Responses to larval herbivory in the phenylpropanoid pathway of Ulmus minor are boosted by prior insect egg deposition

Elms, which have received insect eggs as a 'warning' of larval herbivory, enhance their anti-herbivore defences by accumulating salicylic acid and amplifying phenylpropanoid-related transcriptional and metabolic responses to hatching larvae. Plant responses to insect eggs can result in intensified defences against hatching larvae. In annual plants, this egg-mediated effect is known to be associated with changes in leaf phenylpropanoid levels. However, little is known about how trees-long-living, perennial plants-improve their egg-mediated, anti-herbivore defences. The role of phytohormones and the phenylpropanoid pathway in egg-primed anti-herbivore defences of a tree species has until now been left unexplored. Using targeted and untargeted metabolome analyses we studied how the phenylpropanoid pathway of Ulmus minor responds to egg-laying by the elm leaf beetle and subsequent larval feeding. We found that when compared to untreated leaves, kaempferol and quercetin concentrations increased in feeding-damaged leaves with prior egg deposition, but not in feeding-damaged leaves without eggs. PCR analyses revealed that prior insect egg deposition intensified feeding-induced expression of phenylalanine ammonia lyase (PAL), encoding the gateway enzyme of the phenylpropanoid pathway. Salicylic acid (SA) concentrations were higher in egg-treated, feeding-damaged leaves than in egg-free, feeding-damaged leaves, but SA levels did not increase in response to egg deposition alone-in contrast to observations made of Arabidopsis thaliana. Our results indicate that prior egg deposition induces a SA-mediated response in elms to feeding damage. Furthermore, egg deposition boosts phenylpropanoid biosynthesis in subsequently feeding-damaged leaves by enhanced PAL expression, which results in the accumulation of phenylpropanoid derivatives. As such, the elm tree shows similar, yet distinct, responses to insect eggs and larval feeding as the annual model plant A. thaliana.

The transcription factor ORA59 exhibits dual DNA binding specificity that differentially regulates ethylene- and jasmonic acid-induced genes in plant immunity

Jasmonic acid (JA) and ethylene (ET) signaling modulate plant defense against necrotrophic pathogens in a synergistic and interdependent manner, while JA and ET also have independent roles in certain processes, e.g. in responses to wounding and flooding, respectively. These hormone pathways lead to transcriptional reprogramming, which is a major part of plant immunity and requires the roles of transcription factors. ET response factors are responsible for the transcriptional regulation of JA/ET-responsive defense genes, of which ORA59 functions as a key regulator of this process and has been implicated in the JA-ET crosstalk. We previously demonstrated that Arabidopsis (Arabidopsis thaliana) GDSL LIPASE 1 (GLIP1) depends on ET for gene expression and pathogen resistance. Here, promoter analysis of GLIP1 revealed ERELEE4 as the critical cis-element for ET-responsive GLIP1 expression. In a yeast one-hybrid screening, ORA59 was isolated as a specific transcription factor that binds to the ERELEE4 element, in addition to the well-characterized GCC box. We found that ORA59 regulates JA/ET-responsive genes through direct binding to these elements in gene promoters. Notably, ORA59 exhibited a differential preference for GCC box and ERELEE4, depending on whether ORA59 activation is achieved by JA and ET, respectively. JA and ET induced ORA59 phosphorylation, which was required for both activity and specificity of ORA59. Furthermore, RNA-seq and virus-induced gene silencing analyses led to the identification of ORA59 target genes of distinct functional categories in JA and ET pathways. Our results provide insights into how ORA59 can generate specific patterns of gene expression dynamics through JA and ET hormone pathways.

Expression profiling of pathogenesis-related Protein-1 (PR-1) genes from Solanum tuberosum reveals its critical role in phytophthora infestans infection

Pathogen-related (PR) proteins are an integral part of plants' defense mechanisms against various types of biotic and abiotic stresses. A little is known about the importance of these PR proteins in potato defense mechanisms. In the current study, a total of 22 pathogenesis-related 1 genes were identified in the potato genome. All identified proteins possessed the CAP superfamily domain with some other motifs. The cis-acting elements analysis identified several stress-responsive elements, including MYB, ABRE, and MeJRE. The gene duplication events demonstrated purifying and positive selection pressure. Expression profiling showed high transcripts level in root compared to other tissues; however, some genes have tissue-specific expression. Furthermore, the PR-1-5 gene is transcriptionally induced under Phytophthora infestans stress and hormonal (ABA and IAA) treatments. The Real-Time qPCR analysis also validated the RNA-seq data results of genes with maximum expression in roots compared to leaves and stems. The current study results provided basic data for functional characterization and can also use as a reference study for other important crops.

Functional Verification of Two Genes Related to Stripe Rust Resistance in the Wheat-Leymus mollis Introgression Line M8664-3

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most widespread and destructive fungal diseases of wheat worldwide. The cultivation and growth of resistant wheat varieties are the most economical, effective, and environmental friendly methods to control stripe rust. Therefore, it is necessary to use new resistance genes to breed resistant wheat varieties. A single dominant gene temporarily designated as YrM8664-3, from a wheat-Leymus mollis introgression line M8664-3 highly resistant to Chinese predominant Pst races, is a potentially valuable source of stripe rust resistance for breeding. Herein, based on previous YrM8664-3 chromosome location results (bin 4AL13-0.59-0.66 close to 4AL12-0.43-0.59) and expression change information of candidate genes and bioinformatics analysis, several candidate genes with significantly different expression changes were then selected and verified by virus-induced gene silencing (VIGS). Two of the candidate genes temporarily designated as TaFBN [containing plastid lipid-associated proteins (PAP)_fibrillin domain in its protein] and Ta_Pes_BRCT [containing Pescadillo and breast cancer tumour suppressor protein C-terminus (BRCT) domain in its protein], produced the most significant resistance changes in the wheat-Pst interaction system after silencing. These two genes were further verified by Agrobacterium-mediated wheat genetic transformation technology. According to the identification of disease resistance, the resistance function of the candidate gene TaFBN was further verified. Then, the expression of TaFBN under hormone treatment indicated that TaFBN may be related to the salicylic acid (SA) and abscisic acid (ABA) signaling pathways. Combined with the expression of TaFBN in response to environmental stress stimulation, it can be reasonably speculated that TaFBN plays an important role in the resistance of wheat to Pst and is involved in abiotic stress pathways.

A Plant Stress-Responsive Bioreporter Coupled With Transcriptomic Analysis Allows Rapid Screening for Biocontrols of Necrotrophic Fungal Pathogens

Streptomyces are soil-borne Actinobacteria known to produce a wide range of enzymes, phytohormones, and metabolites including antifungal compounds, making these microbes fitting for use as biocontrol agents in agriculture. In this study, a plant reporter gene construct comprising the biotic stress-responsive glutathione S-transferase promoter GSTF7 linked to a luciferase output (GSTF7:luc) was used to screen a collection of Actinobacteria candidates for manipulation of plant biotic stress responses and their potential as biocontrol agents. We identified a Streptomyces isolate (KB001) as a strong candidate and demonstrated successful protection against two necrotrophic fungal pathogens, Sclerotinia sclerotiorum and Rhizoctonia solani, but not against a bacterial pathogen (Pseudomonas syringe). Treatment of Arabidopsis plants with either KB001 microbial culture or its secreted compounds induced a range of stress and defense response-related genes like pathogenesis-related (PR) and hormone signaling pathways. Global transcriptomic analysis showed that both treatments shared highly induced expression of reactive oxygen species and auxin signaling pathways at 6 and 24 h posttreatment, while some other responses were treatment specific. This study demonstrates that GSTF7 is a suitable marker for the rapid and preliminary screening of beneficial bacteria and selection of candidates with potential for application as biocontrols in agriculture, including the Streptomyces KB001 that was characterized here, and could provide protection against necrotrophic fungal pathogens.

Multi-tissue transcriptome analysis of two Begonia species reveals dynamic patterns of evolution in the chalcone synthase gene family

Begonia is an important horticultural plant group, as well as one of the most speciose Angiosperm genera, with over 2000 described species. Genus wide studies of genome size have shown that Begonia has a highly variable genome size, and analysis of paralog pairs has previously suggested that Begonia underwent a whole genome duplication. We address the contribution of gene duplication to the generation of diversity in Begonia using a multi-tissue RNA-seq approach. We chose to focus on chalcone synthase (CHS), a gene family having been shown to be involved in biotic and abiotic stress responses in other plant species, in particular its importance in maximising the use of variable light levels in tropical plants. We used RNA-seq to sample six tissues across two closely related but ecologically and morphologically divergent species, Begonia conchifolia and B. plebeja, yielding 17,012 and 19,969 annotated unigenes respectively. We identified the chalcone synthase gene family members in our Begonia study species, as well as in Hillebrandia sandwicensis, the monotypic sister genus to Begonia, Cucumis sativus, Arabidopsis thaliana, and Zea mays. Phylogenetic analysis suggested the CHS gene family has high duplicate turnover, all members of CHS identified in Begonia arising recently, after the divergence of Begonia and Cucumis. Expression profiles were similar within orthologous pairs, but we saw high inter-ortholog expression variation. Sequence analysis showed relaxed selective constraints on some ortholog pairs, with substitutions at conserved sites. Evidence of pseudogenisation and species specific duplication indicate that lineage specific differences are already beginning to accumulate since the divergence of our study species. We conclude that there is evidence for a role of gene duplication in generating diversity through sequence and expression divergence in Begonia.

Transcriptome analysis of sesame-Macrophomina phaseolina interactions revealing the distinct genetic components for early defense responses

Sesame (Sesamum indicum L.) is an oilseed crop challenged by many biotic stresses. Charcoal rot caused by Macrophomina phaseolina (MP) is one of the most devastating diseases of sesame. Till date, molecular mechanisms of resistance to charcoal rot in sesame is not yet reported. In this study, two sesame variety GT-10 (resistant) and RT-373 (susceptible) were identified with contrasting disease incidence when infected with MP. To get the molecular insight, root samples were collected at 0, 24, 48- and 72-h post inoculation (hpi) with the pathogen and generated RNAseq data was analyzed. A total of 1153 and 1226 differentially expressed genes (DEGS) were identified in GT-10 and RT-373, respectively. During the inoculation with MP, resistant genotype showed high number DEGs at early time point of 24 hpi and when compared to late expression in susceptible genotype at 48 hpi. Distinct clusters were represented for each time period represented by cytochrome P450 83B1-like, single anchor, hypothetical protein C4D60, kirola like and heat shock proteins in the resistant genotype contributing for resistance. Analysis of differentially expressed genes, catalogued the genes involved in synthesis of pathogenesis-related (PR) proteins, MYB, WRKY, leucine zipper protein, bHLH, bZIP and NAC transcription factors, ABC transporters (B, C and G subfamily), glutathione metabolism, secondary metabolites, fatty acid biosynthesis and phytohormones like auxin, abscisic acid, ethylene and gibberellic acid. Additionally, in the resistant response we have found three unique GO terms including ATP binding, ribonucleotide binding and nucleic acid binding in molecular function category. The molecular clues generated through this work will provide an important resource of genes contributing for disease resistance and could prioritize genes for functional validation in the important oil crop.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-01039-6.

Genome-wide association analysis for response of Senegalese sorghum accessions to Texas isolates of anthracnose

Anthracnose disease of sorghum is caused by Colletotrichum sublineola, a filamentous fungus. The genetic basis of resistance to anthracnose in sorghum is largely unclear, especially in Senegalese sorghum germplasm. In this study, 163 Senegalese sorghum accessions were evaluated for response to C. sublineola, and a genome-wide association study (GWAS) was performed to identify genetic variation associated with response to C. sublineola using 193,727 single nucleotide polymorphisms (SNPs) throughout the genome. Germplasm diversity analysis showed low genetic diversity and slow linkage disequilibrium (LD) decay among the Senegalese accessions. Phenotypic analysis resulted in relatively low differences to C. sublineola among the tested population. Genome-wide association study did not identify any significant association based on a strict threshold for the number of SNPs available. However, individual analysis of the top eight SNPs associated with relative susceptibility and resistance identified candidate genes that have been shown to play important roles in plant stress tolerance in previous studies. This study identifies sorghum genes whose annotated properties have known roles in host defense and thus identify them as candidates for use in breeding for resistance to anthracnose.

Feeding of pea leafminer larvae simultaneously activates jasmonic and salicylic acid pathways in plants to release a terpenoid for indirect defense

The pea leafminer, Liriomyza huidobrensis, is an important pest species affecting ornamental crops worldwide. Plant damage consists of oviposition and feeding punctures created by female adult flies as well as larva-bored mines in leaf mesophyll tissues. How plants indirectly defend themselves from these two types of leafminer damage has not been sufficiently investigated. In this study, we compared the indirect defense responses of bean plants infested by either female adults or larvae. Puncturing of leaves by adults released green leaf volatiles and terpenoids, while larval feeding caused plants to additionally emit methyl salicylate and (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT). Puncturing of plants by female adults induced increases in jasmonic acid (JA) and JA-related gene expressions but reduced the expressions of salicylic acid (SA)-related genes. In contrast, JA and SA and their-related gene expression levels were increased significantly by larval feeding. The exogenous application of JA+SA significantly triggered TMTT emission, thereby significantly inducing the orientation behavior of parasitoids. Our study has confirmed that larval feeding can trigger TMTT emission through the activation of both JA and SA pathways to attract parasitoids; however, TMTT alone is less attractive than the complete blend of volatiles released by infested plants.

Overexpression of the Apple (Malus × domestica) MdERF100 in Arabidopsis Increases Resistance to Powdery Mildew

APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factors play important roles in plant development and stress response. Although AP2/ERF genes have been extensively investigated in model plants such as Arabidopsis thaliana, little is known about their role in biotic stress response in perennial fruit tree crops such as apple (Malus × domestica). Here, we investigated the role of MdERF100 in powdery mildew resistance in apple. MdERF100 localized to the nucleus but showed no transcriptional activation activity. The heterologous expression of MdERF100 in Arabidopsis not only enhanced powdery mildew resistance but also increased reactive oxygen species (ROS) accumulation and cell death. Furthermore, MdERF100-overexpressing Arabidopsis plants exhibited differential expressions of genes involved in jasmonic acid (JA) and salicylic acid (SA) signaling when infected with the powdery mildew pathogen. Additionally, yeast two-hybrid and bimolecular fluorescence complementation assays confirmed that MdERF100 physically interacts with the basic helix-loop-helix (bHLH) protein MdbHLH92. These results suggest that MdERF100 mediates powdery mildew resistance by regulating the JA and SA signaling pathways, and MdbHLH92 is involved in plant defense against powdery mildew. Overall, this study enhances our understanding of the role of MdERF genes in disease resistance, and provides novel insights into the molecular mechanisms of powdery mildew resistance in apple.

Identification of maize kernel resistance proteins against Aspergillus flavus by a statistical approach: A predictive model of resistance capacity

Although kernel infection by Aspergillus flavus and pre-harvest aflatoxin contamination of Zea mays grain is a significant crop production problem, not only in Venezuela but also around the world, little progress has been made in identifying proteins and metabolic pathways associated with this pathogen resistance. Usually, a protein with a two-fold expression between control and condition is considered a biomarker of some phenomena, but we think it is essential to evaluate its contribution to resistance. That is why we decided to determine the behavior's resistance capacity in terms of expression levels of an identified protein of maize kernels infected with A. flavus by using a multivariate approach. In this work, we identify 47 of 66 differentially expressed spots with a remarkable contribution to resistance against the fungus Aspergillus flavus. We finally test this approach to know if it can be used as a predictive resistance model and probe it by including theoretical and experimental protein expression profiles of other inoculated maize lines.

AtWAKL10, a Cell Wall Associated Receptor-Like Kinase, Negatively Regulates Leaf Senescence in Arabidopsis thaliana

Receptor-like kinases (RLKs) constitute a large group of cell surface receptors that play crucial roles in multiple biological processes. However, the function of most RLKs in plants has not been extensively explored, and much less for the class of cell wall associated kinases (WAKs) and WAK-like kinases (WAKLs). In this study, analyses of developmental expression patterns uncovered a putative role of AtWAKL10 in modulating leaf senescence, which was further investigated at physiological and molecular levels. The expression level of AtWAKL10 increased with the developmental progression and was rapidly upregulated in senescing leaf tissues. The promoter of AtWAKL10 contains various defense and hormone responsive elements, and its expression could be significantly induced by exogenous ABA, JA and SA. Moreover, the loss-of-function atwakl10 mutant showed earlier senescence along the course of natural development and accelerated leaf senescence under darkness and hormonal stresses, while plants overexpressing AtWAKL10 showed an opposite trend. Additionally, some defense and senescence related WRKY transcription factors could bind to the promoter of AtWAKL10. In addition, deletion and overexpression of AtWAKL10 caused several specific transcriptional alterations, including genes involved in cell extension, cell wall modification, defense response and senescence related WRKYs, which may be implicated in regulatory mechanisms adopted by AtWAKL10 in controlling leaf senescence. Taken together, these results revealed that AtWAKL10 negatively regulated leaf senescence.

Review: Biological functions of major latex-like proteins in plants

Major latex-like proteins (MLPs) have been identified in dicots and monocots. They are members of the birch pollen allergen Bet v 1 family as well as pathogenesis-related proteins class 10. MLPs have two main features. One is binding affinity toward various hydrophobic compounds, such as long-chain fatty acids, steroids, and systemic acquired resistance signals, via its internal hydrophobic cavity or hydrophobic residues on its surface. MLPs transport such compounds to other organs via phloem and xylem vessels and contribute to the expression of physiologically important ligands' activity in the particular organs. The second feature is responses to abiotic and biotic stresses. MLPs are involved in drought and salt tolerance through the mediation of plant hormone signaling pathways. MLPs generate resistance against pathogens by the induction of pathogenesis-related protein genes. Therefore, MLPs play crucial roles in drought and salt tolerance and resistance against pathogens. However, knowledge of MLPs is fragmented, and an overview of them is needed. Herein, we summarize the current knowledge of the biological functions of MLPs, which to our knowledge, is the first review about MLPs that has been reported.