Host-Microbe Interactions: Shaping the Evolution of the Plant Immune Response

Pathogenesis mechanisms of phytopathogen effectors

Plants commonly face the threat of invasion by a wide variety of pathogens and have developed sophisticated immune mechanisms to defend against infectious diseases. However, successful pathogens have evolved diverse mechanisms to overcome host immunity and cause diseases. Different cell structures and unique cellular organelles carried by plant cells endow plant-specific defense mechanisms, in addition to the common framework of innate immune system shared by both plants and animals. Effectors serve as crucial virulence weapons employed by phytopathogens to disarm the plant immune system and promote infection. Here we summarized the many diverse strategies by which phytopathogen effectors overcome plant defense and prospected future perspectives. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology.

An NBS-LRR protein in the Rpp1 locus negates the dominance of Rpp1-mediated resistance against Phakopsora pachyrhizi in soybean

The soybean Rpp1 locus confers resistance to Phakopsora pachyrhizi, causal agent of rust, and resistance is usually dominant over susceptibility. However, dominance of Rpp1-mediated resistance is lost when a resistant genotype (Rpp1 or Rpp1b) is crossed with susceptible line TMG06_0011, and the mechanism of this dominant susceptibility (DS) is unknown. Sequencing the Rpp1 region reveals that the TMG06_0011 Rpp1 locus has a single nucleotide-binding site leucine-rich repeat (NBS-LRR) gene (DS-R), whereas resistant PI 594760B (Rpp1b) is similar to PI 200492 (Rpp1) and has three NBS-LRR resistance gene candidates. Evidence that DS-R is the cause of DS was reflected in virus-induced gene silencing of DS-R in Rpp1b/DS-R or Rpp1/DS-R heterozygous plants with resistance partially restored. In heterozygous Rpp1b/DS-R plants, expression of Rpp1b candidate genes was not significantly altered, indicating no effect of DS-R on transcription. Physical interaction of the DS-R protein with candidate Rpp1b resistance proteins was supported by yeast two-hybrid studies and in silico modeling. Thus, we conclude that suppression of resistance most likely does not occur at the transcript level, but instead probably at the protein level, possibly with Rpp1 function inhibited by binding to the DS-R protein. The DS-R gene was found in other soybean lines, with an estimated allele frequency of 6% in a diverse population, and also found in wild soybean (Glycine soja). The identification of a dominant susceptible NBS-LRR gene provides insight into the behavior of NBS-LRR proteins and serves as a reminder to breeders that the dominance of an R gene can be influenced by a susceptibility allele.

Volatile Organic Compounds from Pythium oligandrum Play a Role in Its Parasitism on Plant-Pathogenic Pythium myriotylum

The oomycete Pythium oligandrum is a soil-inhabiting parasite and predator of both fungi and oomycetes, and uses hydrolytic enzymes extensively to penetrate and hydrolyze its host or prey. Other mechanisms have been studied less, and we investigated the contribution of P. oligandrum-produced volatile organic compounds (VOCs) to parasitism. The growth-inhibiting activity of P. oligandrum VOCs was tested on Pythium myriotylum-a host or prey of P. oligandrum-coupled with electron microscopy, and biochemical and transcriptomic analyses. The P. oligandrum-produced VOCs reduced P. myriotylum growth by 80% and zoospore levels by 60%. Gas chromatography-mass spectrometry (GC-MS) identified 23 VOCs, and methyl heptenone, d-limonene, 2-undecanone, and 1-octanal were potent inhibitors of P. myriotylum growth and led to increased production of reactive oxygen species at a concentration that did not inhibit P. oligandrum growth. Exposure to the P. oligandrum VOCs led to shrinkage of P. myriotylum hyphae and lysis of the cellular membranes and organelles. Transcriptomics of P. myriotylum exposed to the P. oligandrum VOCs at increasing levels of growth inhibition initially showed a strong upregulation of putative detoxification-related genes that was not maintained later. The inhibition of P. myriotylum growth continued immediately after the exposure to the VOCs was discontinued and led to the reduced infection of its plant hosts. The VOCs produced by P. oligandrum could be another factor alongside hydrolytic enzymes contributing to its ecological role as a microbial parasite in particular ecological niches such as in soil, and may also contribute to the biocontrol of diseases using P. oligandrum commercial preparations. IMPORTANCE Microbe-microbe interactions in nature are multifaceted, with multiple mechanisms of action, and are crucial to how plants interact with microbes. Volatile organic compounds (VOCs) have diverse functions, including contributing to parasitism in ecological interactions and potential applications in biocontrol. The microbial parasite P. oligandrum is well known for using hydrolytic enzymes as part of its parasitism. We found that P. oligandrum VOCs reduced the growth of, and caused major damage to, the hyphae of P. myriotylum (a host or prey of P. oligandrum). Transcriptomic analyses of P. myriotylum exposed to the VOCs revealed the upregulation of genes potentially involved in an attempt to detoxify the VOCs. The inhibitory effects of the VOCs had a knock-on effect by reducing the virulence of P. myriotylum toward its plant hosts. The P. oligandrum VOCs could contribute to its ecological role as a microbial parasite. The VOCs analyzed here may also contribute to the biocontrol of diseases using P. oligandrum commercial preparations.

Recent advances on genome-wide association studies (GWAS) and genomic selection (GS); prospects for Fusarium head blight research in Durum wheat

PURPOSE

Wheat is an important cereal crop that is cultivated in different parts of the world. The biotic stresses are the major concerns in wheat-growing nations and are responsible for production loss globally. The change in climate dynamics makes the pathogen more virulent in foothills and tropical regions. There is growing concern about FHB in major wheat-growing nations, and until now, there has been no known potential source of resistance identified in wheat germplasm. The plant pathogen interaction activates the cascade of pathways, genes, TFs, and resistance genes. Pathogenesis-related genes' role in disease resistance is functionally validated in different plant systems. Similarly, Genomewide association Studies (GWAS) and Genomic selection (GS) are promising tools and have led to the discovery of resistance genes, genomic regions, and novel markers. Fusarium graminearum produces deoxynivalenol (DON) mycotoxins in wheat kernels, affecting wheat productivity globally. Modern technology now allows for detecting and managing DON toxin to reduce the risk to humans and animals. This review offers a comprehensive overview of the roles played by GWAS and Genomic selection (GS) in the identification of new genes, genetic variants, molecular markers and DON toxin management strategies.

METHODS

The review offers a comprehensive and in-depth analysis of the function of Fusarium graminearum virulence factors in Durum wheat. The role of GWAS and GS for Fusarium Head Blight (FHB) resistance has been well described. This paper provides a comprehensive description of the various statistical models that are used in GWAS and GS. In this review, we look at how different detection methods have been used to analyze and manage DON toxin exposure.

RESULTS

This review highlights the role of virulent genes in Fusarium disease establishment. The role of genome-based selection offers the identification of novel QTLs in resistant wheat germplasm. The role of GWAS and GS selection has minimized the use of population development through breeding technology. Here, we also emphasized the function of recent technological developments in minimizing the impact of DON toxins and their implications for food safety.

Genome-wide identification, characterization, and expression profile ofNBS-LRRgene family in sweet orange (Citrussinensis)

BACKGROUND

The NBS-LRR (nucleotide-binding site-leucine-rich repeat gene) gene family, known as the plant R (resistance) gene family with the most members, plays a significant role in plant resistance to various external adversity stresses. The NBS-LRR gene family has been researched in many plant species. Citrus is one of the most vital global cash crops, the number one fruit group, and the third most traded agricultural product world wild. However, as one of the largest citrus species, a comprehensive study of the NBS-LRR gene family has not been reported on sweet oranges.

METHODS

In this study, NBS-LRR genes were identified from the Citrus sinensis genome (v3.0), with a comprehensive analysis of this gene family performed, including phylogenetic analysis, gene structure, cis-acting element of a promoter, and chromosomal localization, among others. The expression pattern of NBS-LRR genes was analyzed when sweet orange fruits were infected by Penicillium digitatum, employing experimental data from our research group. It first reported the expression patterns of NBS-LRR genes under abiotic stresses, using three transcript data from NCBI (National Center for Biotechnology Information).

RESULTS

In this study, 111 NBS-LRR genes were identified in the C. sinensis genome (v3.0) and classified into seven subfamilies according to their N-terminal and C-terminal domains. The phylogenetic tree results indicate that genes containing only the NBS structural domain are more ancient in the sweet orange NBS-LRR gene family. The chromosome localization results showed that 111 NBS-LRR genes were distributed unevenly on nine chromosomes, with the most genes distributed on chromosome 1. In addition, we identified a total of 18 tandem duplication gene pairs in the sweet orange NBS-LRR gene family, and based on the Ka/Ks ratio, all of the tandem duplication genes underwent purifying selection. Transcriptome data analysis showed a significant number of NBS-LRR genes expressed under biotic and abiotic stresses, and some reached significantly different levels of expression. It indicates that the NBS-LRR gene family is vital in resistance to biotic and abiotic stresses in sweet oranges.

CONCLUSION

Our study provides the first comprehensive framework on the NBS-LRR family of genes, which provides a basis for further in-depth studies on the biological functions of NBS-LRR in growth, development, and response to abiotic stresses in sweet orange.

The responses of poplars to fungal pathogens: A review of the defensive pathway

Long-lived tree species need to cope with changing environments and pathogens during their lifetime. Fungal diseases cause damage to trees growth and forest nurseries. As model system for woody plants, poplars are also hosts of a large variety of fungus. The defense strategies to fungus are generally associated with the type of fungus, therefore, the defense strategies of poplar against necrotrophic and biotrophic fungus are different. Poplars initiate constitutive defenses and induced defenses based on recognition of the fungus, hormone signaling network cascades, activation of defense-related genes and transcription factors and production of phytochemicals. The means of sensing fungus invasion in poplars are similar with herbs, both of which are mediated by receptor proteins and resistance (R) proteins, leading to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), but poplars have evolved some unique defense mechanisms compared with Arabidopsis due to their longevity. In this paper, current researches on poplar defensive responses to necrotrophic and biotrophic fungus, which mainly include the physiological and genetic aspects, and the role of noncoding RNA (ncRNA) in fungal resistance are reviewed. This review also provides strategies to enhance poplar disease resistance and some new insights into future research directions.

Transcriptional Analysis of Tea Plants (Camellia sinensis) in Response to Salicylic Acid Treatment

Salicylic acid (SA) is an important plant hormone and signal required for establishing resistance to diverse pathogens and plant diseases. The abundant polyphenols in tea plants also defend plants from biotic and abiotic stresses. However, whether exogenous SA would increase the resistance of tea plants to adversity and the relationship between SA and polyphenols are still poorly understood. Here, we carried out SA treatment on tea seedlings and performed transcriptome sequencing. SA treatment inhibited the phenylpropanoid and flavonoid metabolic pathways but promoted the lignin metabolic pathways. The increased accumulation of lignin in tea leaves after treating with SA indicated that lignin might coordinate SA, enhance, and improve plant defense and disease resistance. Simultaneously, an SA-inducible flavonoid glucosyltransferase (CsUGT0554) specifically involved in 7-OH site glycosylation was characterized in vitro. These results provided valuable information about the effects of SA on tea seedlings and the molecular basis for SA-mediated immune responses.

Transcriptome analysis reveals key genes involved in the resistance to Cryphonectria parasitica during early disease development in Chinese chestnut

BACKGROUND

Chestnut blight, one of the most serious branch diseases in Castanea caused by Cryphonectria parasitica, which has ravaged across American chestnut and most of European chestnut since the early twentieth century. Interestingly, the Chinese chestnut is strongly resistant to chestnut blight, shedding light on restoring the ecological status of Castanea plants severely affected by chestnut blight. To better explore the early defense of Chinese chestnut elicited in response to C. parasitica, the early stage of infection process of C. parasitica was observed and RNA sequencing-based transcriptomic profiling of responses of the chestnut blight-resistant wild resource 'HBY-1' at 0, 3 and 9 h after C. parasitica inoculation was performed.

RESULTS

First, we found that 9 h was a critical period for Chinese chestnut infected by C. parasitica, which was the basis of further study on transcriptional activation of Chinese chestnut in response to chestnut blight in the early stage. In the transcriptome analysis, a total of 283 differentially expressed genes were identified between T9 h and Mock9 h, and these DEGs were mainly divided into two clusters, one of which was metabolism-related pathways including biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, amino sugar and nucleotide sugar metabolism, and photosynthesis; the other was related to plant-pathogen interaction and MAPK signal transduction. Meanwhile, the two clusters of pathways could be connected through junction among phosphatidylinositol signaling system, phytohormone signaling pathway and α-Linolenic acid metabolism pathway. It is worth noting that genes associated with JA biosynthesis and metabolic pathway were significantly up-regulated, revealing that the entire JA metabolic pathway was activated in Chinese chestnut at the early stage of chestnut blight infection.

CONCLUSION

We identified the important infection nodes of C. parasitica and observed the morphological changes of Chinese chestnut wounds at the early stage of infection. In response to chestnut blight, the plant hormone and MAPK signal transduction pathways, plant-pathogen interaction pathways and metabolism-related pathways were activated at the early stage. JA biosynthesis and metabolic pathway may be particularly involved in the Chinese chestnut resistance to chestnut blight. These results contributes to verifying the key genes involved in the resistance of Chinese chestnut to C. parasitica.

High ultraviolet-B sensitivity due to lower CPD photolyase activity is needed for biotic stress response to the rice blast fungus, Magnaporthe oryzae

Sensitivity to ultraviolet-B (UVB, 280-315 nm) radiation varies widely among rice (Oryza sativa) cultivars due to differences in the activity of cyclobutane pyrimidines dimer (CPD) photolyase. Interestingly, cultivars with high UVB sensitivity and low CPD photolyase activity have been domesticated in tropical areas with high UVB radiation. Here, we investigated how differences in CPD photolyase activity affect plant resistance to the rice blast fungus, Magnaporthe oryzae, which is one of the other major stresses. We used Asian and African rice cultivars and transgenic lines with different CPD photolyase activities to evaluate the interaction effects of CPD photolyase activity on resistance to M. oryzae. In UVB-resistant rice plants overexpressing CPD photolyase, 12 h of low-dose UVB (0.4 W m^-2) pretreatment enhanced sensitivity to M. oryzae. In contrast, UVB-sensitive rice (transgenic rice with antisense CPD photolyase, A-S; and rice cultivars with low CPD photolyase activity) showed resistance to M. oryzae. Several defense-related genes were upregulated in UVB-sensitive rice compared to UVB-resistant rice. UVB-pretreated A-S plants showed decreased multicellular infection and robust accumulation of reactive oxygen species. High UVB-induced CPD accumulation promoted defense responses and cross-protection mechanisms against rice blast disease. This may indicate a trade-off between high UVB sensitivity and biotic stress tolerance in tropical rice cultivars.

A highly polymorphic effector protein promotes fungal virulence through suppression of plant-associated Actinobacteria

Plant pathogens secrete effector proteins to support host colonization through a wide range of molecular mechanisms, while plant immune systems evolved receptors to recognize effectors or their activities to mount immune responses to halt pathogens. Importantly, plants do not act as single organisms, but rather as holobionts that actively shape their microbiota as a determinant of health. The soil-borne fungal pathogen Verticillium dahliae was recently demonstrated to exploit the VdAve1 effector to manipulate the host microbiota to promote vascular wilt disease in the absence of the corresponding immune receptor Ve1. We identify a multiallelic V. dahliae gene displaying c. 65% sequence similarity to VdAve1, named VdAve1-like (VdAve1L), which shows extreme sequence variation, including alleles that encode dysfunctional proteins, indicative of selection pressure to overcome host recognition. We show that the orphan cell surface receptor Ve2, encoded at the Ve locus, does not recognize VdAve1L. Additionally, we demonstrate that the full-length variant VdAve1L2 possesses antimicrobial activity, like VdAve1, yet with a divergent activity spectrum, that is exploited by V. dahliae to mediate tomato colonization through the direct suppression of antagonistic Actinobacteria in the host microbiota. Our findings open up strategies for more targeted biocontrol against microbial plant pathogens.

The LeEIX Locus Determines Pathogen Resistance in Tomato

The mechanisms underlying the ability of plants to differentiate between pathogens and commensals in their environment are currently unresolved. It has been suggested that spatiotemporal regulation of pattern-recognition receptor (PRR) content could be one of the components providing plants with the ability to distinguish between pathogens and nonpathogenic microbes. The LeEIX PRRs recognize xylanases derived from beneficial or commensal plant colonizers of Trichoderma species, including the xylanase known as EIX. Here, we investigated possible general roles of PRRs from the LeEIX locus in immunity and pathogen resistance in tomato. Mutating the inhibitory PRR LeEIX1, or overexpressing the activating PRR LeEIX2, resulted in resistance to a wide range of pathogens and increased basal and elicited immunity. LeEIX1 knockout caused increases in the expression level of several tested PRRs, including FLS2, as well as bacterial pathogen resistance coupled with an increase in flg22-mediated immunity. The wild tomato relative Solanum pennellii contains inactive LeEIX PRR variants. S. pennellii does not respond to elicitation with the LeEIX PRR ligand EIX. Given that EIX is derived from a mostly nonpathogenic microbe, the connection of its PRRs to disease resistance has not previously been investigated directly. Here, we observed that compared with S. lycopersicum cultivar M82, S. pennellii was more sensitive to several fungal and bacterial pathogens. Our results suggest that the LeEIX locus might determine resistance to fungal necrotrophs, whereas the resistance to biotrophs is effected in combination with a gene/quantitative trait locus not within the LeEIX locus.

A key virulence effector from cyst nematodes targets host autophagy to promote nematode parasitism

Autophagy, an intracellular degradation system conserved in eukaryotes, has been increasingly recognized as a key battlefield in plant-pathogen interactions. However, the role of plant autophagy in nematode parasitism is mostly unknown. We report here the identification of a novel and conserved effector, Nematode Manipulator of Autophagy System 1 (NMAS1), from plant-parasitic cyst nematodes (Heterodera and Globodera spp.). We used molecular and genetic analyses to demonstrate that NMAS1 is required for nematode parasitism. The NMAS1 effectors are potent suppressors of reactive oxygen species (ROS) induced by flg22 and cell death mediated by immune receptors in Nicotiana benthamiana, suggesting a key role of NMAS1 effectors in nematode virulence. Arabidopsis atg mutants defective in autophagy showed reduced susceptibility to nematode infection. The NMAS1 effectors contain predicted AuTophaGy-related protein 8 (ATG8)-interacting motif (AIM) sequences. In planta protein-protein interaction assays further demonstrated that NMAS1 effectors specifically interact with host plant ATG8 proteins. Interestingly, mutation in AIM2 of GrNMAS1 from the potato cyst nematode Globodera rostochiensis abolishes its interaction with potato StATG8 proteins and its activity in ROS suppression. Collectively, our results reveal for the first time that cyst nematodes employ a conserved AIM-containing virulence effector capable of targeting a key component of host autophagy to promote disease.

Transcriptome analysis of sugarcane reveals rapid defense response of SES208 to Xanthomonas albilineans in early infection

BACKGROUND

Diseases are the major factor affecting the quality and yield of sugarcane during its growth and development. However, our knowledge about the factors regulating disease responses remain limited. The present study focuses on identifying genes regulating transcriptional mechanisms responsible for resistance to leaf scald caused by Xanthomonas albilineans in S. spontaneum and S. officinarum.

RESULTS

After inoculation of the two sugarcane varieties SES208 (S. spontaneum) and LA Purple (S. officinarum) with Xanthomonas albilineans, SES208 exhibited significantly greater resistance to leaf scald caused by X. albilineans than did LA Purple. Using transcriptome analysis, we identified a total of 4323 and 1755 differentially expressed genes (DEGs) in inoculated samples of SES208 and LA Purple, respectively. Significantly, 262 DEGs were specifically identified in SES208 that were enriched for KEGG pathway terms such as plant-pathogen interaction, MAPK signaling pathway, and plant hormone signal transduction. Furthermore, we built a transcriptional regulatory co-expression network that specifically identified 16 and 25 hub genes in SES208 that were enriched for putative functions in plant-pathogen interactions, MAPK signaling, and plant hormone signal transduction. All of these essential genes might be significantly involved in resistance-regulating responses in SES208 after X. albilineans inoculation. In addition, we found allele-specific expression in SES208 that was associated with the resistance phenotype of SES208 when infected by X. albilineans. After infection with X. albilineans, a great number of DEGs associated with the KEGG pathways 'phenylpropanoid biosynthesis' and 'flavonoid biosynthesis' exhibited significant expression changes in SES208 compared to LA Purple that might contribute to superior leaf scald resistance in SES208.

CONCLUSIONS

We provided the first systematical transcriptome map that the higher resistance of SES208 is associated with and elicited by the rapid activation of multiple clusters of defense response genes after infection by X. albilineans and not merely due to changes in the expression of genes generically associated with stress resistance. These results will serve as the foundation for further understanding of the molecular mechanisms of resistance against X. albilineans in S. spontaneum.

Appressoria-Small but Incredibly Powerful Structures in Plant-Pathogen Interactions

Plant-pathogenic fungi are responsible for many of the most severe crop diseases in the world and remain very challenging to control. Improving current protection strategies or designating new measures based on an overall understanding of molecular host-pathogen interaction mechanisms could be helpful for disease management. The attachment and penetration of the plant surface are the most important events among diverse plant-fungi interactions. Fungi evolved as small but incredibly powerful infection structure appressoria to facilitate attachment and penetration. Appressoria are indispensable for many diseases, such as rusts, powdery mildews, and blast diseases, as well as devastating oomycete diseases. Investigation into the formation of plant-pathogen appressoria contributes to improving the understanding of the molecular mechanisms of plant-pathogen interactions. Fungal host attachment is a vital step of fungal pathogenesis. Here, we review recent advances in the molecular mechanisms regulating the formation of appressoria. Additionally, some biocontrol agents were revealed to act on appressorium. The regulation of fungal adhesion during the infective process by acting on appressoria formation is expected to prevent the occurrence of crop disease caused by some pathogenic fungi.

Comprehensive Analysis and Functional Verification of the Pinus massoniana NBS-LRR Gene Family Involved in the Resistance to Bursaphelenchus xylophilus

Pinus massoniana Lamb. is a crucial timber and resin conifer in China, but its plantation industry is threatened by outbreaks of pine wilt disease (PWD) caused by Bursaphelenchus xylophilus (pinewood nematode; PWN). However, as of yet, there is no comprehensive analysis of NBS-LRR genes in P. massoniana involved in its defense against PWN. In this study, 507 NBS genes were identified in the transcriptome of resistant and susceptible P. masoniana inoculated with the PWN. The phylogenetic analysis and expression profiles of resistant and susceptible P. massoniana revealed that the up-regulated PmNBS-LRR97 gene was involved in conferring resistance to PWN. The results of real-time quantitative PCR (qRT-PCR) showed that PmNBS-LRR97 was significantly up-regulated after PWN infection, especially in the stems. Subcellular localization indicated that PmNBS-LRR97 located to the cell membrane. PmNBS-LRR97 significantly activated the expression of reactive oxygen species (ROS)-related genes in P. massoniana. In addition, the overexpression of PmNBS-LRR97 was capable of promoting the production of ROS, aiding in plant growth and development. In summary, PmNBS-LRR97 participates in the defense response to PWN and plays an active role in conferring resistance in P. massoniana. This finding provides new insight into the regulatory mechanism of the R gene in P. massoniana.

Wheat leaf rust fungus effector Pt13024 is avirulent to TcLr30

Wheat leaf rust, caused by Puccinia triticina Eriks. (Pt), is a global wheat disease threatening wheat production. Dissecting how Pt effector proteins interact with wheat has great significance in understanding the pathogenicity mechanisms of Pt. In the study, the cDNA of Pt 13-5-72 interacting with susceptible cultivar Thatcher was used as template to amplify Pt13024 gene. The expression pattern and structure of Pt13024 were analyzed by qRT-PCR and online softwares. The secretion function of Pt13024 signal peptide was verified by the yeast system. Subcellular localization of Pt13024 was analyzed using transient expression on Nicotiana benthamiana. The verification that Pt13024 inhibited programmed cell death (PCD) was conducted on N. benthamiana and wheat. The deletion mutation of Pt13024 was used to identify the virulence function motif. The transient transformation of wheat mediated by the type III secretion system (TTSS) was used to analyze the activity of regulating the host defense response of Pt13024. Pt13024 gene silencing was performed by host-induced gene silencing (HIGS). The results showed that Pt13024 was identified as an effector and localized in the cytoplasm and nucleus on the N. benthamiana. It can inhibit PCD induced by the Bcl-2-associated X protein (BAX) from mice and infestans 1 (INF1) from Phytophthora infestans on N. benthamiana, and it can also inhibit PCD induced by DC3000 on wheat. The amino acids 22 to 41 at N-terminal of the Pt13024 are essential for the inhibition of programmed cell death (PCD) induced by BAX. The accumulation of reactive oxygen species and deposition of callose in near-isogenic line TcLr30, which is in Thatcher background with Lr30, induced by Pt13024 was higher than that in 41 wheat leaf rust-resistant near-isogenic lines (monogenic lines) with different resistance genes and Thatcher. Silencing of Pt13024 reduced the leaf rust resistance of Lr30 during the interaction between Pt and TcLr30. We can conclude that Pt13024 is avirulent to TcLr30 when Pt interacts with TcLr30. These findings lay the foundation for further investigations into the role of Pt effector proteins in pathogenesis and their regulatory mechanisms.

miRNAs and lncRNAs in tomato: Roles in biotic and abiotic stress responses

Plants are continuously exposed to various biotic and abiotic stresses in the natural environment. To cope with these stresses, they have evolved a multitude of defenses mechanisms. With the rapid development of genome sequencing technologies, a large number of non-coding RNA (ncRNAs) have been identified in tomato, like microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Recently, more and more evidence indicates that many ncRNAs are involved in plant response to biotic and abiotic stresses in tomato. In this review, we summarize recent updates on the regulatory roles of ncRNAs in tomato abiotic/biotic responses, including abiotic (high temperature, drought, cold, salinization, etc.) and biotic (bacteria, fungi, viruses, insects, etc.) stresses. Understanding the molecular mechanisms mediated by ncRNAs in response to these stresses will help us to clarify the future directions for ncRNA research and resistance breeding in tomato.

Genome-wide identification and analysis of the NLR gene family in Medicago ruthenica

Medicago ruthenica, important forage in the legume family, possesses high nutritional value and carries abundant tolerance genes. This study used whole-genome data of M. ruthenica to perform a genome-wide analysis of the nucleotide-binding site-leucine-rich repeat receptor (NLR) gene family, which is the largest family of plant disease resistance genes (R genes). A total of 338 NLR genes were identified in the M. ruthenica genome, including 160 typical genes that contained 80 coiled-coil (CC)-NBS-LRR (CNL) genes, 76 toll/interleukin-1 receptor (TIR)-NBS-LRR (TNL) genes, four resistance to powdery mildew 8 (RPW8)-NBS-LRR (RNL) subclass genes, and 178 atypical NLR genes encoding proteins without at least one important domain. Among its eight chromosomes, M. ruthenica chromosomes 3 and 8 contained most of the NLR genes. More than 40% of all NLR genes were located on these two chromosomes, mainly in multigene clusters. The NLR proteins of M. ruthenica had six highly conserved motifs: P-loop, GLPL, RNBS-D, kinase-2, RNBS-C, and MHDV. Phylogenetic analysis revealed that the NLR genes of M. ruthenica formed three deeply separated clades according to the N-terminal domain of the proteins encoded by these genes. Gene duplication and syntenic analysis suggested four gene duplication types in the NLR genes of M. ruthenica, namely, tandem, proximal, dispersed, and segmental duplicates, which involved 189, 49, 59, and 41 genes, respectively. A total of 41 segmental duplication genes formed 23 NLR gene pairs located on syntenic chromosomal blocks mainly between chromosomes 6 and 7. In addition, syntenic analysis between M. truncatula and M. ruthenica revealed 193 gene pairs located on syntenic chromosomal blocks of the two species. The expression analysis of M. ruthenica NLR genes showed that 303 (89.6%) of the NLR genes were expressed in different varieties. Overall, this study described the full NLR profile of the M. ruthenica genome to provide an important resource for mining disease-resistant genes and disease-resistant breeding.

Natural immunity stimulation using ELICE16INDURES® plant conditioner in field culture of soybean

Recently, climate change has had an increasing impact on the world. Innate defense mechanisms operating in plants - such as PAMP-triggered Immunity (PTI) - help to reduce the adverse effects caused by various abiotic and biotic stressors. In this study, the effects of ELICE16INDURES® plant conditioner for organic farming, developed by the Research Institute for Medicinal Plants and Herbs Ltd. Budakalász Hungary, were studied in a soybean population in Northern Hungary. The active compounds and ingredients of this product were selected in such a way as to facilitate the triggering of general plant immunity without the presence and harmful effects of pathogens, thereby strengthening the healthy plant population and preparing it for possible stress effects. In practice, treatments of this agent were applied at two different time points and two concentrations. The conditioning effect was well demonstrated by using agro-drone and ENDVI determination in the soybean field. The genetic background of healthier plants was investigated by NGS sequencing, and by the expression levels of genes encoding enzymes involved in the catalysis of metabolic pathways regulating PTI. The genome-wide transcriptional profiling resulted in 13 contigs related to PAMP-triggered immunity and activated as a result of the treatments. Further analyses showed 16 additional PTI-related contigs whose gene expression changed positively as a result of the treatments. The gene expression values of genes encoded in these contigs were determined by in silico mRNA quantification and validated by RT-qPCR. Both - relatively low and high treatments - showed an increase in gene expression of key genes involving AOC, IFS, MAPK4, MEKK, and GST. Transcriptomic results indicated that the biosyntheses of jasmonic acid (JA), salicylic acid (SA), phenylpropanoid, flavonoid, phytoalexin, and cellular detoxification processes were triggered in the appropriate molecular steps and suggested that plant immune reactions may be activated also artificially, and innate immunity can be enhanced with proper plant biostimulants.

The C-terminal stretch of glycine-rich proline-rich protein (SbGPRP1) from Sorghum bicolor serves as an antimicrobial peptide by targeting the bacterial outer membrane protein

The C-terminal stretch in SbGPRP1 (Sorghum glycine-rich proline-rich protein) acts as an antimicrobial peptide in the host innate defense mechanism. Cationic antimicrobial proteins or peptides can either bind to the bacterial membrane or target a specific protein on the bacterial membrane thus leading to membrane perturbation. The 197 amino acid polypeptide of SbGPRP1 showed disordered structure at the N-terminal end and ordered conformation at the C-terminal end. In the present study, the expression of N-SbGPRP1, C-SbGPRP1, and ∆SbGPRP1 followed by antimicrobial assays showed potential antimicrobial property of the C-terminal peptide against gram-positive bacteria Bacillus subtilis and phytopathogen Rhodococcus fascians. The SbGPRP1 protein loses its antimicrobial property when the 23 amino acid sequence (GHGGHGVFGGGYGHGGYGHGYGG) from position 136 to 158 is deleted from the protein. Thus, it can be concluded that the 23 amino acid sequence is vital for the said antimicrobial property. NPN assay, SEM analysis, and electrolyte leakage assays showed potent antimicrobial activity for C-SbGPRP1. Overexpression of the C-SbGPRP1 mutant protein in tobacco followed by infection with Rhodococcus fascians inhibited bacterial growth as shown by SEM analysis. To determine if C-SbGPRP1 might target any protein on the bacterial membrane we isolated the bacterial membrane protein from both Bacillus subtilis and Rhodococcus fascians. Bacterial membrane protein that interacted with the column-bound C-SbGPRP1 was eluted and subjected to LC-MS/MS. LC-MS/MS data analysis showed peptide hit with membrane protein YszA from Bacillus subtilis and a membrane protein from Rhodococcus fascians. Isolated bacterial membrane protein from Bacillus subtilis or Rhodococcus fascians was able to reduce the antimicrobial activity of C-SbGPRP1. Furthermore, BiFC experiments showed interactions between C-SbGPRP1 and YszA protein from Bacillus subtilis leading to the conclusion that bacterial membrane protein was targeted in such membrane perturbation leading to antimicrobial activity.

PBS3: a versatile player in and beyond salicylic acid biosynthesis in Arabidopsis

AVRPPHB SUSCEPTIBLE 3 (PBS3) belongs to the GH3 family of acyl acid amido synthetases, which conjugates amino acids to diverse acyl acid substrates. Recent studies demonstrate that PBS3 in Arabidopsis plays a key role in the biosynthesis of plant defense hormone salicylic acid (SA) by catalyzing the conjugation of glutamate to isochorismate to form isochorismate-9-glutamate, which is then used to produce SA through spontaneous decay or ENHANCED PSEUDOMONAS SUSCEPTIBILITY (EPS1) catalysis. Consistent with its function as an essential enzyme for SA biosynthesis, PBS3 is well known to be a positive regulator of plant immunity in Arabidopsis. Additionally, PBS3 is also involved in the trade-off between abiotic and biotic stress responses in Arabidopsis by suppressing the inhibitory effect of abscisic acid on SA-mediated plant immunity. Besides stress responses, PBS3 also plays a role in plant development. Under long-day conditions, PBS3 influences Arabidopsis flowering time by regulating the expression of flowering regulators FLOWERING LOCUS C and FLOWERING LOCUS T. Taken together, PBS3 functions in the signaling network of plant development and responses to biotic and/or abiotic stresses, but the molecular mechanisms underlying its diverse roles remain obscure.

The Puccinia striiformis effector Hasp98 facilitates pathogenicity by blocking the kinase activity of wheat TaMAPK4

The obligate biotrophic fungus Puccinia striiformis f. sp. tritici (Pst) employs virulence effectors to disturb host immunity and causes devastating stripe rust disease. However, our understanding of how Pst effectors regulate host defense responses remains limited. In this study, we determined that the Pst effector Hasp98, which is highly expressed in Pst haustoria, inhibits plant immune responses triggered by flg22 or nonpathogenic bacteria. Overexpression of Hasp98 in wheat (Triticum aestivum) suppressed avirulent Pst-triggered immunity, leading to decreased H₂ O₂ accumulation and promoting P. striiformis infection, whereas stable silencing of Hasp98 impaired P. striiformis pathogenicity. Hasp98 interacts with the wheat mitogen-activated protein kinase TaMAPK4, a positive regulator of plant resistance to stripe rust. The conserved TEY motif of TaMAPK4 is important for its kinase activity, which is required for the resistance function. We demonstrate that Hasp98 inhibits the kinase activity of TaMAPK4 and that the stable silencing of TaMAPK4 compromises wheat resistance against P. striiformis. These results suggest that Hasp98 acts as a virulence effector to interfere with the MAPK signaling pathway in wheat, thereby promoting P. striiformis infection.

Structural insight into chitin perception by chitin elicitor receptor kinase 1 of Oryza sativa

Plants have developed innate immune systems to fight against pathogenic fungi by monitoring pathogenic signals known as pathogen-associated molecular patterns (PAMP) and have established endo symbiosis with arbuscular mycorrhizal (AM) fungi through recognition of mycorrhizal (Myc) factors. Chitin elicitor receptor kinase 1 of Oryza sativa subsp. Japonica (OsCERK1) plays a bifunctional role in mediating both chitin-triggered immunity and symbiotic relationships with AM fungi. However, it remains unclear whether OsCERK1 can directly recognize chitin molecules. In this study, we show that OsCERK1 binds to the chitin hexamer ((NAG)₆ ) and tetramer ((NAG)₄ ) directly and determine the crystal structure of the OsCERK1-(NAG)₆ complex at 2 Å. The structure shows that one OsCERK1 is associated with one (NAG)₆ . Upon recognition, chitin hexamer binds OsCERK1 by interacting with the shallow groove on the surface of LysM2. These structural findings, complemented by mutational analyses, demonstrate that LysM2 is crucial for recognition of both (NAG)₆ and (NAG)₄ . Altogether, these findings provide structural insights into the ability of OsCERK1 in chitin perception, which will lead to a better understanding of the role of OsCERK1 in mediating both immunity and symbiosis in rice.

Bioinformatics analysis and function prediction of NBS-LRR gene family in Broussonetia papyrifera

Most of the currently available disease resistance (R) genes have NBS (nucleotide-binding site) and LRR (leucine-rich-repeat) domain which belongs to the NBS-LRR gene family. The whole genome sequencing of Broussonetia papyrifera provides an important bioinformatics database for the study of the NBS-LRR gene family. In this study, 328 NBS-LRR family genes were identified and classified in B. papyrifera according to different classification schemes, where there are 92 N types, 47 CN type, 54 CNL type, 29 NL types, 55 TN type, and 51 TNL type. Subsequently, we conducted bioinformatics analysis of the NBS-LRR gene family. Classification, motif analysis of protein sequences, and phylogenetic tree studies of the NBS-LRR genes in B. papyrifera provide important basis for the functional study of NBS-LRR family genes. Additionally, we performed structural analysis of the chromosomal location, physicochemical properties, and sequences identified by genetic characterization. In addition, through the analysis of GO enrichment, it was found that NBS-LRR genes were involved in defense responses and were significantly enriched in biological stimulation, immune response, and abiotic stress. In addition, we found that Bp06g0955 was the most sensitive to low temperature and encoded the RPM1 protein by analyzing the low temperature transcriptome data of B. papyrifera. Quantitative results of gene expression after 48 h of Fusarium infection showed that Bp01g3293 increased 14 times after infection, which encodes RPM1 protein. The potential of NBS-LRR gene responsive to biotic and abiotic stresses can be exploited to improve the resistance of B. papyrifera.

Citrus Canker Pathogen, Its Mechanism of Infection, Eradication, and Impacts

Citrus canker is a ravaging bacterial disease threatening citrus crops. Its major types are Asiatic Canker, Cancrosis B, and Cancrosis C, caused by Xanthomonas citri pv. citri (Xcc), Xanthomonas citri pv. aurantifolii pathotype-B (XauB), and pathotype-C (XauC), respectively. The bacterium enters its host through stomata and wounds, from which it invades the intercellular spaces in the apoplast. It produces erumpent corky necrotic lesions often surrounded by a chlorotic halo on the leaves, young stems, and fruits, which causes dark spots, defoliation, reduced photosynthetic rate, rupture of leaf epidermis, dieback, and premature fruit drop in severe cases. Its main pathogenicity determinant gene is pthA, whose variants are present in all citrus canker-causing pathogens. Countries where citrus canker is not endemic adopt different methods to prevent the introduction of the pathogen into the region, eradicate the pathogen, and minimize its dissemination, whereas endemic regions require an integrated management program to control the disease. The main aim of the present manuscript is to shed light on the pathogen profile, its mechanism of infection, and fruitful strategies for disease management. Although an adequate method to completely eradicate citrus canker has not been introduced so far, many new methods are under research to abate the disease.

Plant Signals Anticipate the Induction of the Type III Secretion System in Pseudomonas syringae pv. actinidiae, Facilitating Efficient Temperature-Dependent Effector Translocation

Disease resistance in plants depends on a molecular dialogue with microbes that involves many known chemical effectors, but the time course of the interaction and the influence of the environment are largely unknown. The outcome of host-pathogen interactions is thought to reflect the offensive and defensive capabilities of both players. When plants interact with Pseudomonas syringae, several well-characterized virulence factors contribute to early bacterial pathogenicity, including the type III secretion system (T3SS), which must be activated by signals from the plant and environment to allow the secretion of virulence effectors. The manner in which these signals regulate T3SS activity is still unclear. Here, we strengthen the paradigm of the plant-pathogen molecular dialogue by addressing overlooked details concerning the timing of interactions, specifically the role of plant signals and temperature on the regulation of bacterial virulence during the first few hours of the interaction. Whole-genome expression profiling after 1 h revealed that the perception of plant signals from kiwifruit or tomato extracts anticipated T3SS expression in P. syringae pv. actinidiae compared to apoplast-like conditions, facilitating more efficient effector transport in planta, as revealed by the induction of a temperature-dependent hypersensitive response in the nonhost plant Arabidopsis thaliana Columbia-0 (Col-0). Our results show that in the arms race between plants and bacteria, the temperature-dependent timing of bacterial virulence versus the induction of plant defenses is probably one of the fundamental parameters governing the outcome of the interaction. IMPORTANCE Plant diseases-their occurrence and severity-result from the impact of three factors: the host, the pathogen, and the environmental conditions, interconnected in the disease triangle. Time was further included as a fourth factor accounting for plant disease, leading to a more realistic three-dimensional disease pyramid to represent the evolution of disease over time. However, this representation still considers time only as a parameter determining when and to what extent a disease will occur, at a scale from days to months. Here, we show that time is a factor regulating the arms race between plants and pathogens, at a scale from minutes to hours, and strictly depends on environmental factors. Thus, besides the arms possessed by pathogens and plants per se, the opportunity and the timing of arms mobilization make the difference in determining the outcome of an interaction and thus the occurrence of plant disease.

Foliar Pathogen Infection Manipulates Soil Health through Root Exudate-Modified Rhizosphere Microbiome

Negative plant-soil feedback (NPSF) due to the buildup of soilborne pathogens in soil is a major obstacle in sustainable agricultural systems. Beneficial rhizosphere microfloras are recruited by plants, and mediating this has become a strategic priority to manipulate plant health. Here, we found that foliar infection of Panax notoginseng by Alternaria panax changed plant-soil feedback from negative to positive. Foliar infection modified the rhizosphere soil microbial community and reversed the direction of the buildup of the soilborne pathogen Ilyonectria destructans and beneficial microbes, including Trichoderma, Bacillus, and Streptomyces, in rhizosphere soil. These beneficial microbes not only showed antagonistic ability against the pathogen I. destructans but also enhanced the resistance of plants to A. panax. Foliar infection enhanced the exudation of short- and long-chain organic acids, sugars, and amino acids from roots. In vitro and in vivo experiments validated that short- and long-chain organic acids and sugars play dual roles in simultaneously suppressing pathogens but enriching beneficial microbes. In summary, foliar infection could change root secretion to drive shifts in the rhizosphere microbial community to enhance soil health, providing a new strategy to alleviate belowground disease in plants through aboveground inducement. IMPORTANCE Belowground soilborne disease is the main factor limiting sustainable agricultural production and is difficult to manage due to the complexity of the soil environment. Here, we found that aboveground parts of plants infected by foliar pathogens could enhance the secretion of organic acids, sugars, and amino acids in root exudates to suppress soilborne pathogens and enrich beneficial microbes, eventually changing the plant and soil feedback from negative to positive and alleviating belowground soilborne disease. This is an exciting strategy by which to achieve belowground soilborne disease management by manipulating the aboveground state through aboveground stimulation.

Continuous monitoring of chemical signals in plants under stress

Time is an often-neglected variable in biological research. Plants respond to biotic and abiotic stressors with a range of chemical signals, but as plants are non-equilibrium systems, single-point measurements often cannot provide sufficient temporal resolution to capture these time-dependent signals. In this article, we critically review the advances in continuous monitoring of chemical signals in living plants under stress. We discuss methods for sustained measurement of the most important chemical species, including ions, organic molecules, inorganic molecules and radicals. We examine analytical and modelling approaches currently used to identify and predict stress in plants. We also explore how the methods discussed can be used for applications beyond a research laboratory, in agricultural settings. Finally, we present the current challenges and future perspectives for the continuous monitoring of chemical signals in plants.

MdWRKY120 Enhance Apple Susceptibility to Alternaria alternata

Alternaria alternata (A. alternata) is a common pathogen that greatly influences apples' quantity and quality. However, chemical treatments produce increased health risks along with decreased food and environmental safety. Advancements in plant molecular biology, such as transgenic technology, have increased apple trees' resistance to pathogens and have therefore attracted widespread attention. WRKY transcription factors are involved in abiotic and biotic stress regulation; however, their biological role in non-model plants such as apple, is still unknown. In this investigation, MdWRKY120 was isolated from the 'GL-3' apple to determine its function during Alternaria alternate infection. The MdWRKY120-GFP fusion protein was located in the nucleus. MdWRKY120 in yeast cells exhibited activating transcriptional activity, meaning it is a transcription activator. MdWRKY120 overexpression transgenic plants were more sensitive to A. alternata, while RNAi transgenic plants showed increased resistance to A. alternata. This investigation demonstrates that MdWRKY120 enhances the susceptibility of apples to A. alternata.

SH3P2, an SH3 domain-containing protein that interacts with both Pib and AvrPib, suppresses effector-triggered, Pib-mediated immunity in rice

Plants usually keep resistance (R) proteins in a static state under normal conditions to avoid autoimmunity and save energy for growth, but R proteins can be rapidly activated upon perceiving pathogen invasion. Pib, the first cloned blast disease R gene in rice, encoding a nucleotide-binding leucine-rich repeat (NLR) protein, mediates resistance to the blast fungal (Magnaporthe oryzae) isolates carrying the avirulence gene AvrPib. However, the molecular mechanisms about how Pib recognizes AvrPib and how it is inactivated and activated remain largely unclear. In this study, through map-based cloning and CRISPR-Cas9 gene editing, we proved that Pib contributes to the blast disease resistance of rice cultivar Yunyin (YY). Furthermore, an SH3 domain-containing protein, SH3P2, was found to associate with Pib mainly at clathrin-coated vesicles in rice cells, via direct binding with the coiled-coil (CC) domain of Pib. Interestingly, overexpression of SH3P2 in YY compromised Pib-mediated resistance to M. oryzae isolates carrying AvrPib and Pib-AvrPib recognition-induced cell death. SH3P2 competitively inhibits the self-association of the Pib CC domain in vitro, suggesting that binding of SH3P2 with Pib undermines its homodimerization. Moreover, SH3P2 can also interact with AvrPib and displays higher affinity to AvrPib than to Pib, which leads to dissociation of SH3P2 from Pib in the presence of AvrPib. Taken together, our results suggest that SH3P2 functions as a "protector" to keep Pib in a static state by direct interaction during normal growth but could be triggered off by the invasion of AvrPib-carrying M. oryzae isolates. Our study reveals a new mechanism about how an NLR protein is inactivated under normal conditions but is activated upon pathogen infection.

Sigma factor binding protein 1 (CsSIB1) is a putative candidate of the major-effect QTL dm5.3 for downy mildew resistance in cucumber (Cucumis sativus)

The dm5.3 major-effect QTL in cucumber encodes a homolog of Arabidopsis sigma factor binding protein 1 (CsSIB1). CsSIB1 positively regulates defense responses against downy mildew in cucumber through the salicylic acid (SA) biosynthesis/signaling pathway. Downy mildew (DM) caused by the oomycete pathogen Pseudoperonospora cubensis is an important disease of cucumber and other cucurbits. Our knowledge on molecular mechanisms of DM resistance is still limited. In this study, we reported identification and functional characterization of the candidate gene for the major-effect QTL, dm5.3 for DM resistance originated from PI 197088. The dm5.3 QTL was Modelized through marker-assisted development of near isogenic lines (NILs). NIL-derived segregating populations were used for fine mapping which narrowed the dm5.3 locus down to a 144 kb region. Based on multiple lines of evidence, we show that CsSIB1 (CsGy5G027140) that encodes the VQ motif-containing sigma factor binding protein 1 as the most likely candidate for dm5.3. Local association analysis identified a haplotype consisting of 7 SNPs inside the coding and promoter region of CsSIB1 that was associated with DM resistance. Expression of CsSIB1 was up-regulated with P. cubensis infection. Transcriptome profiling of NILs in response to P. cubensis inoculation revealed key players and associated gene networks in which increased expression of CsSIB1 antagonistically promoted salicylic acid (SA) but suppressed jasmonic acid (JA) biosynthesis/signaling pathways. Our work provides novel insights into the function of CsSIB1/dm5.3 as a disease resistance (R) gene. The roles of sigma factor binding protein genes in pathogen defense in cucumber were also discussed.

An in-planta comparative study of Plasmopara viticola proteome reveals different infection strategies towards susceptible and Rpv3-mediated resistance hosts

Plasmopara viticola, an obligate biotrophic oomycete, is the causal agent of one of the most harmful grapevine diseases, downy mildew. Within this pathosystem, much information is gathered on the host, as characterization of pathogenicity and infection strategy of a biotrophic pathogen is quite challenging. Molecular insights into P. viticola development and pathogenicity are just beginning to be uncovered, mainly by transcriptomic studies. Plasmopara viticola proteome and secretome were only predicted based on transcriptome data. In this study, we have identified the in-planta proteome of P. viticola during infection of a susceptible ('Trincadeira') and a Rpv3-mediated resistance ('Regent') grapevine cultivar. Four hundred and twenty P. viticola proteins were identified on a label-free mass spectrometry-based approach of the apoplastic fluid of grapevine leaves. Overall, our study suggests that, in the compatible interaction, P. viticola manipulates salicylic-acid pathway and isoprenoid biosynthesis to enhance plant colonization. Furthermore, during the incompatible interaction, development-associated proteins increased while oxidoreductases protect P. viticola from ROS-associated plant defence mechanism. Up to our knowledge this is the first in-planta proteome characterization of this biotrophic pathogen, thus this study will open new insights into our understanding of this pathogen colonization strategy of both susceptible and Rpv3-mediated resistance grapevine genotypes.

RNA-seq Gene Profiling Reveals Transcriptional Changes in the Late Phase during Compatible Interaction between a Korean Soybean Cultivar (Glycine max cv. Kwangan) and Pseudomonas syringae pv. syringae B728a

Soybean (Glycine max (L) Merr.) provides plant-derived proteins, soy vegetable oils, and various beneficial metabolites to humans and livestock. The importance of soybean is highly underlined, especially when carbon-negative sustainable agriculture is noticeable. However, many diseases by pests and pathogens threaten sustainable soybean production. Therefore, understanding molecular interaction between diverse cultivated varieties and pathogens is essential to developing disease-resistant soybean plants. Here, we established a pathosystem of the Korean domestic cultivar Kwangan against Pseudomonas syringae pv. syringae B728a. This bacterial strain caused apparent disease symptoms and grew well in trifoliate leaves of soybean plants. To examine the disease susceptibility of the cultivar, we analyzed transcriptional changes in soybean leaves on day 5 after P. syringae pv. syringae B728a infection. About 8,900 and 7,780 differentially expressed genes (DEGs) were identified in this study, and significant proportions of DEGs were engaged in various primary and secondary metabolisms. On the other hand, soybean orthologs to well-known plant immune-related genes, especially in plant hormone signal transduction, mitogen-activated protein kinase signaling, and plant-pathogen interaction, were mainly reduced in transcript levels at 5 days post inoculation. These findings present the feature of the compatible interaction between cultivar Kwangan and P. syringae pv. syringae B728a, as a hemibiotroph, at the late infection phase. Collectively, we propose that P. syringae pv. syringae B728a successfully inhibits plant immune response in susceptible plants and deregulates host metabolic processes for their colonization and proliferation, whereas host plants employ diverse metabolites to protect themselves against infection with the hemibiotrophic pathogen at the late infection phase.

Pathways to engineering the phyllosphere microbiome for sustainable crop production

Current disease resistance breeding, which is largely dependent on the exploitation of resistance genes in host plants, faces the serious challenges of rapidly evolving phytopathogens. The phyllosphere is the largest biological surface on Earth and an untapped reservoir of functional microbiomes. The phyllosphere microbiome has the potential to defend against plant diseases. However, the mechanisms of how the microbiota assemble and function in the phyllosphere remain largely elusive, and this restricts the exploitation of the targeted beneficial microbes in the field. Here we review the endogenous and exogenous cues impacting microbiota assembly in the phyllosphere and how the phyllosphere microbiota in turn facilitate the disease resistance of host plants. We further construct a holistic framework by integrating of holo-omics, genetic manipulation, culture-dependent characterization and emerging artificial intelligence techniques, such as deep learning, to engineer the phyllosphere microbiome for sustainable crop production.

The function of the plant cell wall in plant-microbe interactions

The plant cell wall is an interface of plant-microbe interactions. The ability of microbes to decompose cell wall polysaccharides contributes to microbial pathogenicity. Plants have evolved mechanisms to prevent cell wall degradation. However, the role of the cell wall in plant-microbe interactions is not well understood. Here, we discuss four functions of the plant cell wall-physical defence, storage of antimicrobial compounds, production of cell wall-derived elicitors, and provision of carbon sources-in the context of plant-microbe interactions. In addition, we discuss the four families of cell surface receptors associated with plant cell walls (malectin-like receptor kinase family, wall-associated kinase family, leucine-rich repeat receptor-like kinase family, and lysin motif receptor-like kinase family) that have been the subject of several important studies in recent years. This review summarises the findings on both plant cell wall and plant immunity, improving our understanding and may provide impetus to various researchers.

Stem and leaf rust-induced miRNAome in bread wheat near-isogenic lines and their comparative analysis

Wheat rusts remain a major threat to global wheat production and food security. The R-gene-mediated resistance has been employed as an efficient approach to develop rust-resistant varieties. However, evolution of new fungal races and infection strategies put forward the urgency of unravelling novel molecular players, including non-coding RNAs for plant response. This study identified microRNAs associated with Sr36 and Lr45 disease resistance genes in response to stem and leaf rust, respectively. Here, small RNA sequencing was performed on susceptible and resistant wheat near-isogenic lines inoculated with stem and leaf rust pathotypes. microRNA mining in stem rust-inoculated cultivars revealed a total of distinct 26 known and 7 novel miRNAs, and leaf rust libraries culminated with 22 known and 4 novel miRNAs. The comparative analysis between two disease sets provides a better understanding of altered miRNA profiles associated with respective R-genes and infections. Temporal differential expression pattern of miRNAs pinpoints their role during the progress of infection. Differential expression pattern of miRNAs among various treatments as well as time-course expression of miRNAs revealed stem and leaf rust-responsive miRNAs and their possible role in balancing disease resistance/susceptibility. Disclosure of guide strand, passenger strand and a variant of novel-Tae-miR02 from different subgenome origins might serve as a potential link between stem and leaf rust defence mechanisms downstream to respective R-genes. The outcome from the analysis of microRNA dynamics among two rust diseases and further characterization of identified microRNAs can contribute to significant novel insights on wheat-rust interactions and rust management. KEY POINTS: • Identification and comparative analysis of stem and leaf rust-responsive miRNAs. • Chromosomal location and functional prediction of miRNAs. • Time-course expression analysis of pathogen-responsive miRNAs.

A single amino acid transporter controls the uptake of priming-inducing beta-amino acids and the associated tradeoff between induced resistance and plant growth

Selected β-amino acids, such as β-aminobutyric acid (BABA) and R-β-homoserine (RBH), can prime plants for resistance against a broad spectrum of diseases. Here, we describe a genome-wide screen of fully annotated Arabidopsis thaliana T-DNA insertion lines for impaired in RBH-induced immunity (iri) mutants against the downy mildew pathogen Hyaloperonospora arabidopsidis, yielding 104 lines that were partially affected and four lines that were completely impaired in RBH-induced resistance (IR). We confirmed the iri1-1 mutant phenotype with an independent T-DNA insertion line in the same gene, encoding the high-affinity amino acid transporter LYSINE HISTIDINE TRANSPORTER 1 (LHT1). Uptake experiments with yeast cells expressing LHT1 and mass spectrometry-based quantification of RBH and BABA in leaves of lht1 mutant and LHT1 overexpression lines revealed that LHT1 acts as the main transporter for cellular uptake and systemic distribution of RBH and BABA. Subsequent characterization of lht1 mutant and LHT1 overexpression lines for IR and growth responses revealed that the levels of LHT1-mediated uptake determine the tradeoff between IR and plant growth by RBH and BABA.

Genetic requirements for infection-specific responses in conferring disease resistance in Arabidopsis

Immunity in plants arises from defense regulatory circuits that can be conceptualized as modules. Both the types (and isolates) of pathogen and the repertoire of plant receptors may cause different modules to be activated and affect the magnitude of activation. Two major defense enzymes of Arabidopsis are ALD1 and ICS1/SID2. ALD1 is an aminotransferase needed for producing the metabolites pipecolic acid, hydroxy-pipecolic acid, and possibly other defense signals. ICS1/SID2 produces isochorismate, an intermediate in the synthesis of salicylic acid (SA) and SA-derivatives. Metabolites resulting from the activation of these enzymes are found in petiole exudates and may serve as priming signals for systemic disease resistance in Arabidopsis. Mutants lacking ALD1 are known to have reduced SA accumulation. To further investigate the role of ALD1 in relation to the SA-related module, immunity phenotypes of double mutants that disrupt ALD1 and ICS1/SID2 or SA perception by NPR1 were compared with each single mutant after infection by different Pseudomonas strains. Exudates collected from these mutants after infection were also evaluated for their ability to confer disease resistance when applied to wild-type plants. During infection with virulent or attenuated strains, the loss of ALD1 does not increase the susceptibility of npr1 or sid2 mutants, suggesting the main role of ALD1 in this context is in amplifying the SA-related module. In contrast, after an infection that leads to strong pathogen recognition via the cytoplasmic immune receptor RPS2, ALD1 acts additively with both NPR1 and ICS1/SID2 to suppress pathogen growth. The additive effects are observed in early basal defense responses as well as SA-related events. Thus, there are specific conditions that dictate whether the modules independently contribute to immunity to provide additive protection during infection. In the exudate experiments, intact NPR1 and ICS1/SID2, but not ALD1 in the donor plants were needed for conferring immunity. Mixing exudates showed that loss of SID2 yields exudates that suppress active exudates from wild-type or ald1 plants. This indicates that ICS1/SID2 may not only lead to positive defense signals, but also prevent a suppressive signal(s).

Climate change impedes plant immunity mechanisms

Rapid climate change caused by human activity is threatening global crop production and food security worldwide. In particular, the emergence of new infectious plant pathogens and the geographical expansion of plant disease incidence result in serious yield losses of major crops annually. Since climate change has accelerated recently and is expected to worsen in the future, we have reached an inflection point where comprehensive preparations to cope with the upcoming crisis can no longer be delayed. Development of new plant breeding technologies including site-directed nucleases offers the opportunity to mitigate the effects of the changing climate. Therefore, understanding the effects of climate change on plant innate immunity and identification of elite genes conferring disease resistance are crucial for the engineering of new crop cultivars and plant improvement strategies. Here, we summarize and discuss the effects of major environmental factors such as temperature, humidity, and carbon dioxide concentration on plant immunity systems. This review provides a strategy for securing crop-based nutrition against severe pathogen attacks in the era of climate change.

A Bacillus licheniformis Glycoside Hydrolase 43 Protein Is Recognized as a MAMP

Glycoside hydrolases from pathogens have often been reported as inducers of immune responses. However, the roles of glycoside hydrolase from plant-growth-promoting rhizobacteria (PGPR) in the resistance of plants against pathogens is not well studied. In this study, we identified a glycoside hydrolase 43 protein, H1AD43, produced by Bacillus licheniformis BL06 that can trigger defense responses, including cell death. Ion-exchange and size-exclusion chromatography were used for separation, and the amino acid sequence was identified by mass spectrometry. The recombinant protein generated by prokaryotic expression was able to elicit a hypersensitive response (HR) in Nicotiana benthamiana and trigger early defense responses, including reactive oxygen species (ROS) burst, callose accumulation, and the induction of defense genes. In addition, the protein could induce resistance in N. benthamiana, in which it inhibited infection by Phytophthora capsici Leonian and tobacco mosaic virus-green fluorescent protein (TMV-GFP) expression. H1AD43 thus represents a microbe-associated molecular pattern (MAMP) of PGPR that induces plant disease resistance and may provide a new method for the biological control of plant disease.

The Gain-of-Function Mutation, OsSpl26, Positively Regulates Plant Immunity in Rice

Rice spotted-leaf mutants are ideal materials to study the molecular mechanism underlying programmed cell death and disease resistance in plants. LOC_Os07g04820 has previously been identified as the candidate gene responsible for the spotted-leaf phenotype in rice Spotted-leaf 26 (Spl26) mutant. Here, we cloned and validated that LOC_Os07g04820 is the locus controlling the spotted-leaf phenotype of Spl26 by reverse functional complementation and CRISPR/Cas9-mediated knockout of the mutant allele. The recessive wild-type spl26 allele (Oryza sativa spotted-leaf 26, Osspl26) is highly conservative in grass species and encodes a putative G-type lectin S-receptor-like serine/threonine protein kinase with 444 amino acid residuals. OsSPL26 localizes to the plasma membrane and can be detected constitutively in roots, stems, leaves, sheaths and panicles. The single base substitution from T to A at position 293 leads to phenylalanine/tyrosine replacement at position 98 in the encoded protein in the mutant and induces excessive accumulation of H₂O₂, leading to oxidative damage to cells, and finally, formation of the spotted-leaf phenotype in Spl26. The formation of lesions not only affects the growth and development of the plants but also activates the defense response and enhances the resistance to the bacterial blight pathogen, Xanthomonas oryzae pv. oryzae. Our results indicate that the gain-of-function by the mutant allele OsSpl26 positively regulates cell death and immunity in rice.

Enhanced Resistance to Sclerotinia sclerotiorum in Brassica rapa by Activating Host Immunity through Exogenous Verticillium dahliae Aspf2-like Protein (VDAL) Treatment

Sclerotinia stem rot caused by Sclerotinia sclerotiorum is one of the most destructive diseases in Brassica rapa. Verticillium dahliae Aspf2-like protein (VDAL) is a secretory protein of V. dahliae which has been shown to enhance the resistance against fungal infections in several plants. Nonetheless, the molecular mechanisms of VDAL-primed disease resistance are still poorly understood. In this study, we performed physiological, biochemical, and transcriptomic analyses of Brassica rapa in order to understand how VDAL confers resistance to S. sclerotiorumn infections in plants. The results showed that foliar application of VDAL significantly reduced the plaque area on leaves inoculated with S. sclerotiorum. It also enhanced antioxidant capacity by increasing activities of superoxide dismutase (SOD), peroxidase (POD), peroxidase (APX), glutathione reductase (GR), protoporphyrinogen oxidase (PPO), and defense-related enzymes β-1,3-glucanase and chitinase during the infection periods. This occurred in parallel with significantly reduced relative conductivity at different periods and lower malondialdehyde (MDA) content as compared to sole S. sclerotiorum inoculation. Transcriptomic analysis showed a total of 146 (81 up-regulated and 65 down-regulated) differentially expressed genes (DEGs) in VDAL-treated leaves compared to the control. The most enriched three Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the mitogen-activated protein kinase (MAPK) signaling pathway, plant hormone signal transduction, and plant-pathogen interaction, all of which were associated with plant immunity. DEGs associated with MAPK and hormone signal transduction pathways were ethylene response sensor ERS2, EIN3 (Ethylene Insensitive3)-binding F-box protein 2 (EBF2), ethylene-responsive transcription factor ERF94, MAPK 9 (MKK9), protein phosphatase 2C (PP2C37), auxin-responsive proteins (AUX/IAA1 and 19), serine/threonine-protein kinase CTR1, and abscisic acid receptors (PLY 4 and 5). Among the DEGs linked with the plant-pathogen interaction pathway were calmodulin-like proteins (CML5, 24, 27), PTI1-like tyrosine protein kinase 3 (Pti13) and transcription factor MYB30, all of which are known to play key roles in pathogen-associated molecular pattern (PAMP)-triggered immunity and effector-triggered immunity (ETI) for hypersensitive response (HR), cell wall reinforcement, and stomatal closure in plants. Overall, VDLA treatment triggered repression of the auxin and ABA signaling pathways and de-repression of the ethylene signaling pathways in young B. rapa seedlings to increase plant innate immunity. Our results showed that VDAL holds great potential to enhance fungal disease resistance in B. rapa crop.

Predicting Cloned Disease Resistance Gene Homologs (CDRHs) in Radish, Underutilised Oilseeds, and Wild Brassicaceae Species

Brassicaceae crops, including Brassica, Camelina and Raphanus species, are among the most economically important crops globally; however, their production is affected by several diseases. To predict cloned disease resistance (R) gene homologs (CDRHs), we used the protein sequences of 49 cloned R genes against fungal and bacterial diseases in Brassicaceae species. In this study, using 20 Brassicaceae genomes (17 wild and 3 domesticated species), 3172 resistance gene analogs (RGAs) (2062 nucleotide binding-site leucine-rich repeats (NLRs), 497 receptor-like protein kinases (RLKs) and 613 receptor-like proteins (RLPs)) were identified. CDRH clusters were also observed in Arabis alpina, Camelina sativa and Cardamine hirsuta with assigned chromosomes, consisting of 62 homogeneous (38 NLR, 17 RLK and 7 RLP clusters) and 10 heterogeneous RGA clusters. This study highlights the prevalence of CDRHs in the wild relatives of the Brassicaceae family, which may lay the foundation for rapid identification of functional genes and genomics-assisted breeding to develop improved disease-resistant Brassicaceae crop cultivars.

Salicylic acid inhibits gibberellin signaling through receptor interactions

It is well known that plants activate defense responses at the cost of growth. However, the underlying molecular mechanisms are not well understood. The phytohormones salicylic acid (SA) and gibberellin (GA) promote defense response and growth, respectively. Here we show that SA inhibits GA signaling to repress plant growth. We found that the SA receptor NPR1 interacts with the GA receptor GID1. Further biochemical studies revealed that NPR1 functions as an adaptor of ubiquitin E3 ligase to promote the polyubiquitination and degradation of GID1, which enhances the stability of DELLA proteins, the negative regulators of GA signaling. Genetic analysis suggested that NPR1, GID1, and DELLA proteins are all required for the SA-mediated growth inhibition. Collectively, our study not only uncovers a novel regulatory mechanism of growth-defense trade-off but also reveals the interaction of hormone receptors as a new mode of hormonal crosstalk.

Transcriptome Profiling of the Resistance Response of Musa acuminata subsp. burmannicoides, var. Calcutta 4 to Pseudocercospora musae

Banana (Musa spp.), which is one of the world’s most popular and most traded fruits, is highly susceptible to pests and diseases. Pseudocercospora musae, responsible for Sigatoka leaf spot disease, is a principal fungal pathogen of Musa spp., resulting in serious economic damage to cultivars in the Cavendish subgroup. The aim of this study was to characterize genetic components of the early immune response to P. musae in Musa acuminata subsp. burmannicoides, var. Calcutta 4, a resistant wild diploid. Leaf RNA samples were extracted from Calcutta 4 three days after inoculation with fungal conidiospores, with paired-end sequencing conducted in inoculated and non-inoculated controls using lllumina HiSeq 4000 technology. Following mapping to the reference M. acuminata ssp. malaccensis var. Pahang genome, differentially expressed genes (DEGs) were identified and expression representation analyzed on the basis of gene ontology enrichment, Kyoto Encyclopedia of Genes and Genomes orthology and MapMan pathway analysis. Sequence data mapped to 29,757 gene transcript models in the reference Musa genome. A total of 1073 DEGs were identified in pathogen-inoculated cDNA libraries, in comparison to non-inoculated controls, with 32% overexpressed. GO enrichment analysis revealed common assignment to terms that included chitin binding, chitinase activity, pattern binding, oxidoreductase activity and transcription factor (TF) activity. Allocation to KEGG pathways revealed DEGs associated with environmental information processing, signaling, biosynthesis of secondary metabolites, and metabolism of terpenoids and polyketides. With 144 up-regulated DEGs potentially involved in biotic stress response pathways, including genes involved in cell wall reinforcement, PTI responses, TF regulation, phytohormone signaling and secondary metabolism, data demonstrated diverse early-stage defense responses to P. musae. With increased understanding of the defense responses occurring during the incompatible interaction in resistant Calcutta 4, these data are appropriate for the development of effective disease management approaches based on genetic improvement through introgression of candidate genes in superior cultivars.

Digital gene expression profiling of the transcriptional response to Sclerotinia sclerotiorum and its antagonistic bacterium Bacillus amyloliquefaciens in soybean

Soybean Sclerotinia stem rot caused by Sclerotinia sclerotiorum is a common disease in soybean, and effective biological control is urgently needed. We have previously confirmed that Bacillus amyloliquefaciens can effectively antagonize S. sclerotiorum in a plate competition experiment and a soybean seedling inoculation experiment. In this study, the mechanisms underlying plant death caused by S. sclerotiorum and soybean resistance to S. sclerotiorum induced by B. amyloliquefaciens were evaluated. The stems of potted soybean seedlings were inoculated with S. sclerotiorum (Gm-Ss), B. amyloliquefaciens (Gm-Ba), and their combination (Gm-Ba-Ss), using scratch treatments as a control, followed by dual RNA sequencing and bioinformatics analyses. Global gene expression levels in the Gm-Ss treatment were much lower than those in the Gm-Ba, Gm-Ba-Ss, and Gm groups, suggesting that S. sclerotiorum strongly inhibited global gene expression in soybean. In a pairwise comparison of Gm-Ss vs. Gm, 19983 differentially expressed genes (DEGs) were identified. Down-regulated DEGs were involved in various KEGG pathways, including ko01110 (biosynthesis of secondary metabolites), ko01100 (metabolic pathways), ko01120 (microbial metabolism in diverse environments), ko00500 (starch and sucrose metabolism), and ko04075 (plant hormone signal transmission), suggesting that S. sclerotiorum inoculation had a serious negative effect on soybean metabolism. In Gm-Ba vs. Gm, 13091 DEGs were identified, and these DEGs were significantly enriched in ko03010 (ribosome) and ko03008 (ribosome biogenesis in eucaryotes). Our results suggest that B. amyloliquefaciens increases the expression of genes encoding the ribosomal subunit, promotes cell wall biogenesis, and induces systemic resistance. S. sclerotiorum strongly inhibited metabolism in soybean, inhibited the synthesis of the cytoskeleton, and induced the up-regulation of programmed death and senescence-related genes via an ethylene signal transduction pathway. These results improve our understanding of S. sclerotiorum-induced plant death and soybean resistance to S. sclerotiorum induced by B. amyloliquefaciens and may contribute to the improvement of strategies to avoid yield losses.

Genome-Based Multi-Antigenic Epitopes Vaccine Construct Designing against Staphylococcus hominis Using Reverse Vaccinology and Biophysical Approaches

Staphylococcus hominis is a Gram-positive bacterium from the staphylococcus genus; it is also a member of coagulase-negative staphylococci because of its opportunistic nature and ability to cause life-threatening bloodstream infections in immunocompromised patients. Gram-positive and opportunistic bacteria have become a major concern for the medical community. It has also drawn the attention of scientists due to the evaluation of immune evasion tactics and the development of multidrug-resistant strains. This prompted the need to explore novel therapeutic approaches as an alternative to antibiotics. The current study aimed to develop a broad-spectrum, multi-epitope vaccine to control bacterial infections and reduce the burden on healthcare systems. A computational framework was designed to filter the immunogenic potent vaccine candidate. This framework consists of pan-genomics, subtractive proteomics, and immunoinformatics approaches to prioritize vaccine candidates. A total of 12,285 core proteins were obtained using a pan-genome analysis of all strains. The screening of the core proteins resulted in the selection of only two proteins for the next epitope prediction phase. Eleven B-cell derived T-cell epitopes were selected that met the criteria of different immunoinformatics approaches such as allergenicity, antigenicity, immunogenicity, and toxicity. A vaccine construct was formulated using EAAAK and GPGPG linkers and a cholera toxin B subunit. This formulated vaccine construct was further used for downward analysis. The vaccine was loop refined and improved for structure stability through disulfide engineering. For an efficient expression, the codons were optimized as per the usage pattern of the E coli (K12) expression system. The top three refined docked complexes of the vaccine that docked with the MHC-I, MHC-II, and TLR-4 receptors were selected, which proved the best binding potential of the vaccine with immune receptors; this was followed by molecular dynamic simulations. The results indicate the best intermolecular bonding between immune receptors and vaccine epitopes and that they are exposed to the host’s immune system. Finally, the binding energies were calculated to confirm the binding stability of the docked complexes. This work aimed to provide a manageable list of immunogenic and antigenic epitopes that could be used as potent vaccine candidates for experimental in vivo and in vitro studies.

Melatonin and Indole-3-Acetic Acid Synergistically Regulate Plant Growth and Stress Resistance

Plant growth and development exhibit plasticity, and plants can adapt to environmental changes and stress. Various phytohormones interact synergistically or antagonistically to regulate these responses. Melatonin and indole-3-acetic acid (IAA) are widespread across plant kingdom. Melatonin, an important member of the neuroendocrine immune regulatory network, can confer autoimmunity and protect against viral invasion. Melatonin functions as a plant growth regulator and biostimulant, with an important role in enhancing plant stress tolerance. IAA has a highly complex stress response mechanism, which participates in a series of stress induced physiological changes. This article reviews studies on the signaling pathways of melatonin and IAA, focusing on specific regulatory mechanisms. We discuss how these hormones coordinate plant growth and development and stress responses. Furthermore, the interactions between melatonin and IAA and their upstream and downstream transcriptional regulation are discussed from the perspective of modulating plant development and stress adaptation. The reviewed studies suggest that, at low concentrations, melatonin promotes IAA synthesis, whereas at high levels it reduces IAA levels. Similarly to IAA, melatonin promotes plant growth and development. IAA suppresses the melatonin induced inhibition of germination. IAA signaling plays an important role in plant growth and development, whereas melatonin signaling plays an important role in stress responses.

Bio-Inspired Rhamnolipids, Cyclic Lipopeptides and a Chito-Oligosaccharide Confer Protection against Wheat Powdery Mildew and Inhibit Conidia Germination

Plant protection is mainly based on the application of synthetic pesticides to limit yield losses resulting from diseases. However, the use of more eco-friendly strategies for sustainable plant protection has become a necessity that could contribute to controlling pathogens through a direct antimicrobial effect and/or an induction of plant resistance. Three different families of natural or bioinspired compounds originated from bacterial or fungal strains have been evaluated to protect wheat against powdery mildew, caused by the biotrophic Blumeria graminis f.sp. tritici (Bgt). Thus, three bio-inspired mono-rhamnolipids (smRLs), three cyclic lipopeptides (CLPs, mycosubtilin (M), fengycin (F), surfactin (S)) applied individually and in mixtures (M + F and M + F + S), as well as a chitosan oligosaccharide (COS) BioA187 were tested against Bgt, in planta and in vitro. Only the three smRLs (Rh-Eth-C12, Rh-Est-C12 and Rh-Succ-C12), the two CLP mixtures and the BioA187 led to a partial protection of wheat against Bgt. The higher inhibitor effects on the germination of Bgt spores in vitro were observed from smRLs Rh-Eth-C12 and Rh-Succ-C12, mycosubtilin and the two CLP mixtures. Taking together, these results revealed that such molecules could constitute promising tools for a more eco-friendly agriculture.

Acidovorax citrulli Effector AopV Suppresses Plant Immunity and Interacts with Aromatic Dehydratase ADT6 in Watermelon

Bacterial fruit blotch (BFB) is a disease of cucurbit plants caused by Acidovorax citrulli. Although A. citrulli has great destructive potential, the molecular mechanisms of pathogenicity of A. citrulli are not clear, particularly with regard to its type III secreted effectors. In this study, we characterized the type III secreted effector protein, AopV, from A. citrulli strain Aac5. We show that AopV significantly inhibits reactive oxygen species and the expression of PTI marker genes, and helps the growth of Pseudomonas syringae D36E in Nicotiana benthamiana. In addition, we found that the aromatic dehydratase ADT6 from watermelon was a target of AopV. AopV interacts with ADT6 in vivo and in vitro. Subcellular localization indicated ADT6 and AopV were co-located at the cell membrane. Together, our results reveal that AopV suppresses plant immunity and targets ADT6 in the cell membrane. These findings provide an new characterization of the molecular interaction of A. citrulli effector protein AopV with host cells.