Host Plant Research Articles

Changes in DNA methylation contribute to rapid adaptation in bacterial plant pathogen evolution

Adaptation is usually explained by beneficial genetic mutations that are transmitted from parents to offspring and become fixed in the adapted population. However, genetic mutation analysis alone is not sufficient to fully explain the adaptive processes, and several studies report the existence of nongenetic (or epigenetic) inheritance that can enable adaptation to new environments. In the present work, we tested the hypothesis of the role of DNA methylation, a form of epigenetic modification, in adaptation of the plant pathogen Ralstonia pseudosolanacearum to the host during experimental evolution. Using SMRT-seq technology, we analyzed the methylomes of 31 experimentally evolved clones obtained after serial passages on 5 different plant species during 300 generations. Comparison with the methylome of the ancestral clone revealed a list of 50 differential methylated sites (DMSs) at the GTWWAC motif. Gene expression analysis of the 39 genes targeted by these DMSs revealed limited correlation between differential methylation and differential expression of the corresponding genes. Only 1 gene showed a correlation, the RSp0338 gene encoding the EpsR regulator protein. The MSRE-qPCR technology, used as an alternative approach for DNA methylation analysis, also found the 2 DMSs upstream RSp0338. Using site-directed mutagenesis, we demonstrated the contribution of these 2 DMSs in host adaptation. As these DMSs appeared very early in the experimental evolution, we hypothesize that such fast epigenetic changes can allow rapid adaptation to the plant stem environment. In addition, we found that the change in DNA methylation upstream RSp0338 remains stable at least for 100 generations outside the host and thus can contribute to long-term adaptation to the host plant. To our knowledge, this is the first study showing a direct link between bacterial epigenetic variation and adaptation to a new environment.

Bioactive Compounds Produced by Endophytic Bacteria and Their Plant Hosts—An Insight into the World of Chosen Herbaceous Ruderal Plants in Central Europe

Bioactive Compounds Produced by Endophytic Bacteria and Their Plant Hosts—An Insight into the World of Chosen Herbaceous Ruderal Plants in Central Europe

Plant-parasitic nematode Xiphinema parataylori Lazarova et al., 2019 (Nematoda: Longidoridae) from Poland: first report outside the place of species original description

Plant-parasitic nematodes of the genus Xiphinema Cobb, 1913 constitute a group of soilinhabiting, polyphagous ectoparasites of plant roots, some of which are also vectors of nepoviruses. In this study, 1237 soil samples were taken from different regions of Poland. In two of these samples (0.16% of all collected) Xiphinema parataylori Lazarova et al., 2019 was present, which constitutes not only the first record from Poland but also the first report outside the Czech Republic and Slovakia, where this species was initially described. Specimens from Poland were largely similar to those from the original description except for a slenderer body (maximal body thickness in two populations found 44.8 and 46.8 vs 54, 55 and 56 μm resulting in higher ‘a’ index: 50.0 and 50.8 vs 37.8, 40.7 and 41.2). Specimens from the Polish populations were also characterized based on the ITS1 molecular marker. Finally, both populations recorded from Poland were associated with wild pear (Pyrus pyraster) extending the number of known host plants.

Interactions between host plant quality and non‐consumptive predator effects on oviposition and larval behaviour of Plutella xylostella (Lepidoptera: Plutellidae)

Abstract The presence of predators can induce non‐consumptive effects on prey that result in subsequent changes to prey behaviour and defence. We investigate the interaction between top‐down non‐consumptive effects of various stages of the predator Coccinella septempunctata L.(Coleoptera: Coccinellidae) (larvae and adult) and bottom‐up effects of host nutrition on Plutella xylostella (L.) (Lepidoptera: Plutellidae) oviposition and larval host choice. We also compare the effect of presence of intact predators, predators without mandibles, confined predators and a no predator control treatment on P. xylostella larval growth, survival and herbivory. Host plant nutrition influenced the host choice of adult female P. xylostella; no interaction was observed between bottom‐up host plant nutrition and the presence of C. septempunctata adults or larvae on oviposition or larval host choice by P. xylostella. Predator presence impacted larval feeding and weight gain. The presence of free‐moving C. septempunctata adults without mandibles that could not predate P. xylostella reduced mean leaf consumption by P. xylostella larvae to 1.88 ± 0.21 cm2 and reduced weight gain to 2.12 ± 0.16 mg. Despite differences in leaf damage and larval weight gain, survival remained consistent across the non‐consumptive treatments. Intact C. septempunctata larvae reduced leaf damage and subsequent P. xylostella larval weight gain. The presence of larval predators across the non‐consumptive treatments, however, had no effect on feeding damage or weight gain. Results of our investigation indicate that C. septempunctata causes some non‐consumptive effects on P. xylostella that depend on predator life stage, level of confinement and prey life stage. It is likely that P. xylostella responds to multi‐modal cues in predator detection.

Taxonogenomic analysis of the Xanthomonas translucens complex leads to the descriptions of Xanthomonas cerealis sp. nov. and Xanthomonas graminis sp. nov.

The pathovar-based taxonomy of the Xanthomonas translucens group is very confusing due to an overlap of plant host ranges and level of host specificity. Here, whole-genome sequence-based parameters (digital DNA–DNA hybridization and blast-based average nucleotide identity), phylogenomic, biochemical and phenotypical data were used to taxonomically analyse the 11 known pathovars of the X. translucens complex. This polyphasic approach taxonomically assigned the 11 pathovars of X. translucens complex into three distinct species, two of which are new: X. translucens, X. cerealis sp. nov. and X. graminis sp. nov. X. translucens consists of three pathovars: pv. translucens (=pv. hordei), pv. pistaciae strain A ICMP 16316PT and pv. undulosa (=pv. secalis). X. cerealis sp. nov. encompasses the pv. cerealis strain LMG 679PT and pv. pistaciae strain B ICMP 16317PT with genome similarity of 92.7% (dDDH) and 99.0% (ANIb) suggesting taxonomically similar genotypes. The other new species, X. graminis sp. nov., consists of the remaining five designated pathovars (pv. graminis, pv. arrhenatheri, pv. poae, pv. phleipratensis and pv. phlei) with highly variable dDDH and ANIb values ranging from 74.5 to 93.0% and from 96.7 to 99.2%, respectively, an indication of a very divergent taxonomic group. Only strains of pvs. phlei and phleipratensis showed the highest genomic similarities of 93.0% (dDDH) and 99.2% (ANIb), suggesting synonymic pathovars as both infect the same plant hosts. The dDDH and ANI data were corroborated by phylogenomics clustering. The fatty acid contents were similar but the type strain of X. graminis sp. nov. exhibited 20% less C15 : 0 iso and 40% more C17 : 0 iso fatty acids than the other species. Based on phenotypic, biochemical and whole-genome sequence data, we propose two new species, Xanthomonas cerealis sp. nov. and Xanthomonas graminis sp. nov. with type strains LMG 679T (=NCPPB 1944T) and LMG 726T (=NCPPB 2700T), respectively.

Whole genome regulatory effect of MoISW2 and consequences for the evolution of the rice plant pathogenic fungus Magnaporthe oryzae.

Isw2 proteins, ubiquitous across eukaryotes, exhibit a propensity for DNA binding and exert dynamic influences on local chromosome condensation in an ATP-dependent fashion, thereby modulating the accessibility of neighboring genes to transcriptional machinery. Here, we report the deletion of a putative MoISW2 gene, yielding substantial ramifications on plant pathogenicity. Subsequent gene complementation and chromatin immunoprecipitation sequencing (ChIP-seq) analyses were conducted to delineate binding sites. RNA sequencing (RNA-seq) assays revealed discernible impacts on global gene regulation along chromosomes in both mutant and wild-type strains, with comparative analyses against 55 external RNA-seq data sets corroborating these findings. Notably, MoIsw2-mediated binding and activities delineate genomic loci characterized by pronounced gene expression variability proximal to MoIsw2 binding sites, juxtaposed with comparatively stable expression in surrounding regions. The contingent genes influenced by MoIsw2 activity predominantly encompass niche-determinant genes, including those encoding secreted proteins, secondary metabolites, and stress-responsive elements, alongside avirulence genes. Furthermore, our investigations unveil a spatial correlation between MoIsw2 binding motifs and known transposable elements (TEs), suggesting a potential interplay wherein TE transposition at these loci could modulate the transcriptional landscape of Magnaporthe oryzae in a strain-specific manner. Collectively, these findings position MoIsw2 as a plausible master regulator orchestrating the delicate equilibrium between genes vital for biomass proliferation, akin to housekeeping genes, and niche-specific determinants crucial for ecological adaptability. Stress-induced TE transposition, in conjunction with MoIsw2 activity, emerges as a putative mechanism fostering enhanced mutagenesis and accelerated evolution of niche-determinant genes relative to housekeeping counterparts.IMPORTANCEIsw2 proteins are conserved in plants, fungi, animals, and other eukaryotes. We show that a fungal Isw2 protein in the rice pathogen Magnaporthe oryzae binds to retrotransposon (RT) DNA motifs and affects the epigenetic gene expression landscape of the fungal genome. Mainly ecological niche determinant genes close to the binding motifs are affected. RT elements occur frequently in DNA between genes in most organisms. They move place and multiply in the genome, especially under physiological stress. We further discuss the Isw2 and RT combined activities as a possible sought-after mechanism that can cause biased mutation rates and faster evolution of genes necessary for reacting to abiotic and biotic challenges. The most important biotic challenges for plant pathogens are the ones from the host plants' innate immunity. The overall result of these combined activities will be an adaptation-directed evolution of niche-determinant genes.

First report of Rhizoctonia blight caused by Rhizoctonia solani on Chinese cabbage (Brassica rapa subsp. chinensis) in India.

During January and February 2021, foliar blight symptoms were observed on the leaves of Chinese cabbage (Pak choi) at Lembucherra research farm, College of Agriculture, Tripura, India. The incidence of disease symptoms ranged from 5 to 10% of the plants observed in the field. The symptomatic leaves showed grayish colored water-soaked lesions with an irreguar shape and size. A total of 10 symptomatic leaves (1 leaf per plant) from Chinese cabbage infected plant were sampled, surface decontaminated with 1% NaOCl, washed twice in sterile water, plated on 2% water agar, and incubated at 25 ± 2°C. Hyphal tips from mycelium of 7-day old culture (2 isolates from two different plants) with right-angled branching were transferred to potato dextrose agar (PDA) media (SRL, India). Cream or light brown hyphae that branched at right angles, with septa near the point of the origin of hyphae, and a slight constriction at the base of the branch) were visible under a microscope. Olive-brown sclerotia were observed after 5 days of incubation. Multiple nuclei per cell were visible after staining with 4', 6-diamidino-2-phenylindole (Estandarte et al. 2016). Based on morphological characteristics (Parmeter et al. 1970) the isolates TP36 and TP37 were identified as Rhizoctonia solani. The internal transcribed spacer (ITS) region and glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH) were amplified with ITS1& ITS4 (White et al. 1990) and (GAPDH F-5'- CAAGGAGAACCCAGGTGTTAAG-3' and GAPDH R- 5'-GGCGTCGAAGATAGAAGAGTGT-3') respectively for both isolates and sequenced (accession #. PP458158, PP458159, PP425343, PP425344). BLASTn analysis showed 99.26%( 668/673 nt) to 99.46% (659/664 nt) identity with R. solani sequences (GenBank MG397062.1 and KX674524.1) for ITS and 98.42% (552/562 nt) to 100% 540/540 nt)identity with R. solani sequences (GenBank HQ425709.1 and CP102644.1) for GAPDH. Isolates TP36 and TP37 were deposited in the Indian Type Culture Collection (ITCC), New Delhi as R. solani (nos. 9154 and 9319, respectively). Both isolates were amplified using (anastomosis group) AG1 subgroup specific primers (Matsumoto 2002; Prashantha et al. 2021) to identify their AG. The presence of a 265 bp amplicon for both isolates suggested that they belong to AG1-IA. A multilocus analysis of R. solani isolates from different host plants with concatenated sequences ITS and GAPH showed that TP36 and TP37 are closely related to rice isolate RS107. A pathogenicity test on five plants per treatment was conducted and repeated twice on one month old Chinese cabbage plants (hybrid, TOKITA, India) grown under glasshouse conditions in a sterilized mixture of soil and sand (3:1) at 27-28oC during January 2024 at ICAR-IARI, New Delhi. R. solani isolates TP36 and TP37 were grown on PDA and plants were inoculated by placing single sclerotia of 10-day old colony on different plant parts and covering it with moist cotton. After 7 day, typical lesions of R. solani infection were visible. No symptoms were observed on the control plants. The fungus was reisolated from the inoculated plants and identified as R. solani based on morphology. R. solani has previously been reported to cause disease on some members of Brassicaceae in different countries (Budge et al. 2009; Hua et al. 2014). Based on literature available this is the first report of R. solani infecting Chinese cabbage in India.

Transcriptomic profiling reveals the complex interaction between a bipartite begomovirus and a cucurbitaceous host plant

BackgroundBegomoviruses are major constraint in the production of many crops. Upon infection, begomoviruses may substantially modulate plant biological processes. While how monopartite begomoviruses interact with their plant hosts has been investigated extensively, bipartite begomoviruses-plant interactions are understudied. Moreover, as one of the major groups of hosts, cucurbitaceous plants have been seldom examined in the interaction with begomoviruses.ResultsWe profiled the zucchini transcriptomic changes induced by a bipartite begomovirus squash leaf curl China virus (SLCCNV). We identified 2275 differentially-expressed genes (DEGs), of which 1310 were upregulated and 965 were downregulated. KEGG enrichment analysis of the DEGs revealed that many pathways related to primary and secondary metabolisms were enriched. qRT-PCR verified the transcriptional changes of twelve selected DEGs induced by SLCCNV infection. Close examination revealed that the expression levels of all the DEGs of the pathway Photosynthesis were downregulated upon SLCCNV infection. Most DEGs in the pathway Plant-pathogen interaction were upregulated, including some positive regulators of plant defenses. Moreover, the majority of DEGs in the MAPK signaling pathway-plant were upregulated.ConclusionOur findings indicates that SLCCNV actively interact with its cucurbitaceous plant host by suppressing the conversion of light energy to chemical energy and inducing immune responses. Our study not only provides new insights into the interactions between begomoviruses and host plants, but also adds to our knowledge on virus-plant interactions in general.

Endophytic Fungi: A Treasure Trove of Antifungal Metabolites

Emerging and reemerging fungal infections are very common in nosocomial and non-nosocomial settings in people having poor immunogenic profiles either due to hematopoietic stem cell transplants or are using immunomodulators to treat chronic inflammatory disease or autoimmune disorders, undergoing cancer therapy or suffering from an immune weakening disease like HIV. The refractory behavior of opportunistic fungi has necessitated the discovery of unconventional antifungals. The emergence of black fungus infection during COVID-19 also triggered the antifungal discovery program. Natural products are one of the alternative sources of antifungals. Endophytic fungi reside and co-evolve within their host plants and, therefore, offer a unique bioresource of novel chemical scaffolds with an array of bioactivities. Hence, immense possibilities exist that these unique chemical scaffolds expressed by the endophytic fungi may play a crucial role in overcoming the burgeoning antimicrobial resistance. These chemical scaffolds so expressed by these endophytic fungi comprise an array of chemical classes beginning from cyclic peptides, sesquiterpenoids, phenols, anthraquinones, coumarins, etc. In this study, endophytic fungi reported in the last six years (2018–2023) have been explored to document the antifungal entities they produce. Approximately 244 antifungal metabolites have been documented in this period by different groups of fungi existing as endophytes. Various aspects of these antifungal metabolites, such as antifungal potential and their chemical structures, have been presented. Yet another unique aspect of this review is the exploration of volatile antifungal compounds produced by these endophytic fungi. Further strategies like epigenetic modifications by chemical as well as biological methods and OSMAC to induce the silent gene clusters have also been presented to generate unprecedented bioactive compounds from these endophytic fungi.

Mycologists and Virologists Align: Proposing Botrytis cinerea for Global Mycovirus Studies

Mycoviruses are highly genetically diverse and can significantly change their fungal host’s phenotype, yet they are generally under-described in genotypic and biological studies. We propose Botrytis cinerea as a model mycovirus system in which to develop a deeper understanding of mycovirus epidemiology including diversity, impact, and the associated cellular biology of the host and virus interaction. Over 100 mycoviruses have been described in this fungal host. B. cinerea is an ideal model fungus for mycovirology as it has highly tractable characteristics—it is easy to culture, has a worldwide distribution, infects a wide range of host plants, can be transformed and gene-edited, and has an existing depth of biological resources including annotated genomes, transcriptomes, and isolates with gene knockouts. Focusing on a model system for mycoviruses will enable the research community to address deep research questions that cannot be answered in a non-systematic manner. Since B. cinerea is a major plant pathogen, new insights may have immediate utility as well as creating new knowledge that complements and extends the knowledge of mycovirus interactions in other fungi, alone or with their respective plant hosts. In this review, we set out some of the critical steps required to develop B. cinerea as a model mycovirus system and how this may be used in the future.

A remarkable new species of the genus Digitivalva Gaedike, 1970 (Lepidoptera, Glyphipterigidae, Acrolepiinae) from Japan

A new species of the genus Digitivalva Gaedike, 1970 from Japan, D. bella Zhang, Yagi & Hirowatari, sp. nov., is described. The host plant of this species is identified as Carpesium divaricatum Sieb. & Zucc. (Asteraceae). Larvae of this species pupate beneath the host tissue; this habit is for the first time reported for the genus Digitivalva in Japan. Adult specimens with male and female genitalia and pupae are illustrated and described in detail. Although the wing markings differ, the new species is considered closely related to D. arnicella (Heyden, 1863) from Europe, with which it shares similar biological and morphological features.

Influences of Salt Stress on Cotton Metabolism and Its Consequential Effects on the Development and Fecundity of Aphis gossypii Glover

The degree of global soil salinization is gradually deepening, which will inevitably affect agricultural ecology. It has been found that salt stress induces the resistance of host plants to phytophagous pests. However, little is known about the effects of salt-stressed cotton plants on the fitness of cotton aphids (Aphis gossypii Glover). In this study, we investigated the differences between cotton metabolomes under mild (75 mM NaCl) and moderate (150 mM NaCl) salinity conditions and their effects on the fitness of cotton aphids. The results showed that 49 metabolites exhibited significant upregulation, while 86 metabolites were downregulated, with the increasing NaCl concentration. The duration of nymphal aphids under 150 mM NaCl significantly extended to 6.31 days when compared with the control (0 mM NaCl, 4.10 days). Meanwhile, the longevity of adult aphids decreased significantly under 75 and 150 mM NaCl, with an average of 10.38 days (0 mM NaCl) reduced to 8.55 and 4.89 days, respectively. Additionally, the total reproduction number of single females decreased from 31.31 (0 mM NaCl) to 21.13 (75 mM NaCl) and 10.75 (150 mM NaCl), whereas the survival rate of aphids decreased from 81.25% (0 mM NaCl) to 56.25% (75 mM NaCl) and 34.38% (150 mM NaCl) on the 12th day. These results support the hypothesis that plants growing under salt stress are better defended against herbivores. Furthermore, 49 differential metabolites were found to be negatively correlated with the longevity and fecundity of adult aphids, while 86 different metabolites showed the opposite trend. These results provide insights into the occurrence and control of cotton aphids amidst the escalating issue of secondary salinization.

Arbuscular mycorrhizal fungal spore communities and co-occurrence networks demonstrate host-specific variation throughout the growing season.

Microbial community assembly involves a series of ecological filtering mechanisms that determine the composition of microbial communities. While the importance of both broad and local level factors on microbial communities has been reasonably well studied, this work often is limited to single observations and neglects to consider how communities change over time (i.e., seasonal variation). Because seasonal variation is an important determinant of community assembly and determines the relative importance of community assembly filters, this represents a key knowledge gap. Due to their close associations with seasonal variation in plant growth and fitness, arbuscular mycorrhizal (AM) fungi are useful groups for assessing the importance of seasonal dynamics in microbial community assembly. We tested how seasonal variation (spring vs. summer), plant life history stage (vegetative vs. flowering), and host plant species (Baptisia bracteata var. leucophaea & Andropogon gerardii) influenced AM fungal spore community assembly. AM fungal spore community temporal dynamics were closely linked to plant host species and life history stage. While AM fungal spore communities demonstrated strong turnover between the spring (e.g., higher sporulation) and late summer (e.g., higher diversity), the strength and direction of these changes was modified by host plant species. Here we demonstrate the importance of considering temporal variation in microbial community assembly, and also show how plant-microbe interactions can modify seasonal trends in microbial community dynamics.

Histone deacetylase HDAC3 regulates ergosterol production for oxidative stress tolerance in the entomopathogenic and endophytic fungus Metarhizium robertsii.

Oxidative stress is encountered by fungi in almost all niches, resulting in fungal degeneration or even death. Fungal tolerance to oxidative stress has been extensively studied, but the current understanding of the mechanisms regulating oxidative stress tolerance in fungi remains limited. The entomopathogenic and endophytic fungus Metarhizium robertsii encounters oxidative stress when it infects insects and develops a symbiotic relationship with plants, and we found that host reactive oxygen species (ROSs) greatly limited fungal growth in both insects and plants. We identified a histone H3 deacetylase (HDAC3) that catalyzed the deacetylation of lysine 56 of histone H3. Deleting Hdac3 significantly reduced the tolerance of M. robertsii to oxidative stress from insects and plants, thereby decreasing fungal ability to colonize the insect hemocoel and plant roots. HDAC3 achieved this by regulating the expression of three genes in the ergosterol biosynthesis pathway, which includes the lanosterol synthase gene Las1. The deletion of Hdac3 or Las1 reduced the ergosterol content and impaired cell membrane integrity. This resulted in an increase in ROS accumulation in fungal cells that were thus more sensitive to oxidative stress. We further showed that HDAC3 regulated the expression of the three ergosterol biosynthesis genes in an indirect manner. Our work significantly advances insights into the epigenetic regulation of oxidative stress tolerance and the interactions between M. robertsii and its plant and insect hosts.IMPORTANCEOxidative stress is a common challenge encountered by fungi that have evolved sophisticated mechanisms underlying tolerance to this stress. Although fungal tolerance to oxidative stress has been extensively investigated, the current understanding of the mechanisms for fungi to regulate oxidative stress tolerance remains limited. In the model entomopathogenic and plant symbiotic fungus Metarhizium robertsii, we found that the histone H3 deacetylase HDAC3 regulates the production of ergosterol, an essential cell membrane component. This maintains the cell membrane integrity to resist the oxidative stress derived from the insect and plant hosts for successful infection of insects and development of symbiotic associates with plants. Our work provides significant insights into the regulation of oxidative stress tolerance in M. robertsii and its interactions with insects and plants.

The phytopathogen Xanthomonas campestris senses and effluxes salicylic acid via a sensor HepR and an RND family efflux pump to promote virulence in host plants

AbstractSalicylic acid (SA) plays an essential role in plant defense against biotrophic and semi‐biotrophic pathogens. Following pathogen recognition, SA biosynthesis dramatically increases at the infection site of the host plant. The manner in which pathogens sense and tolerate the onslaught of SA stress to survive in the plant following infection remains to be understood. The objective of this work was to determine how the model phytopathogen Xanthomonas campestris pv. campestris (Xcc) senses and effluxes SA during infection inside host plants. First, RNA‐Seq analysis identified an SA‐responsive operon Xcc4167–Xcc4171, encoding a MarR family transcription factor HepR and an RND (resistance‐nodulation‐cell division) family efflux pump HepABCD in Xcc. Electrophoretic mobility shift assays and DNase I footprint analysis revealed that HepR negatively regulated hepABCD expression by specifically binding to an AT‐rich region of the promoter of the hepRABCD operon, Phep. Second, isothermal titration calorimetry and further genetic analysis suggest that HepR is a novel SA sensor. SA binding released HepR from its cognate promoter Phep and then induced the expression of hepABCD. Third, the RND family efflux pump HepABCD was responsible for SA efflux. The hepRABCD cluster was also involved in the regulation of culture pH and quorum sensing signal diffusible signaling factor turnover. Finally, the hepRABCD cluster was transcribed during the XC1 infection of Chinese radish and was required for the full virulence of Xcc in Chinese radish and cabbage. These findings suggest that the ability of Xcc to co‐opt the plant defense signal SA to activate the multidrug efflux pump may have evolved to ensure Xcc survival and virulence in susceptible host plants.

Plasmodiophora brassicae effector PbPE23 induces necrotic responses in both host and non-host plants.

Plasmodiophora brassicae is an obligate biotroph that causes clubroot disease in cruciferous plants, including canola and Arabidopsis. In contrast to most known bacterial, oomycete and fungal pathogens that colonize at the host apoplastic space, the protist P. brassicae establishes an intracellular colonization within various types of root cells and secretes a plethora of effector proteins to distinct cellular compartments favourable for survival and growth of the pathogen during pathogenesis. Identification and functional characterization of P. brassicae effectors has been hampered by the limited understanding of this unique pathosystem. Here, we report a P. brassicae effector, PbPE23, containing a Ser/Thr kinase domain, that induces necrosis after heterologous expression by leaf infiltration in both host and non-host plants. While PbPE23 is an active kinase, the kinase activity itself is not required for triggering the necrosis in plants. PbPE23 shows a nucleocytoplasmic localization in Nicotiana benthamiana and its N-terminal 25TPdPAQKQ32 sequence, resembling the contiguous hydrophilic TPAP motif and Q-rich region in many Nep1-like proteins (NLPs) from plant-associated microbes, is required for the induction of necrosis. Further, transcript profiling of PbPE23 reveals its high expression at the transition stages from primary to secondary infection, suggesting its potential involvement in the development of clubroot disease.

Modulation of Plant Transcription Factors and Priming of Stress Tolerance by Plant Growth-Promoting Bacteria: A Systematic Review.

Plant growth-promoting bacteria (PGPB) have been shown to improve plant growth and stress tolerance through mechanisms including improved access to nutrients and biotic competition with pathogens. As such, the use of PGPB can help to address challenges to crop productivity, however, information on interactions between PGPB and their plant hosts, especially at the level of gene regulation, is distributed across diverse studies involving several different plants and PGPB. For this review, we analysed recent research publications reporting specifically on plant transcription factor (TF) expression in association with PGPB, to determine if there are any common findings and to identify gaps that offer opportunities for focused future research. The inoculation of plants with PGPB elicits a dynamic and temporal response. Initially, there is an upregulation of defence-responsive TFs, followed by their downregulation in an intermediate phase, and finally, another upregulation, providing longer term stress tolerance. PGPB-priming activates plant defences in the form of induced systemic resistance (ISR), often via the MAMP/MAPK pathways and involving one or more of the major plant hormone-signalling pathways and their crosstalk. Following PGPB-priming, the TFs families most commonly reported as expressed across different plants and for different pathogens are ERF and WRKY, while the TFs most commonly expressed across different plants for different abiotic stresses are ERF and DREB. There were inconsistencies between studies regarding the timing of the shift from the initial phase to the intermediate phase, and some of the TFs expressed during this process have not been fully characterized. This calls for more research to investigate the regulatory functions and phases of TF expression, to enhance crop resilience. Most reports on abiotic stresses have focused on salinity and drought, with fewer studies addressing nutrient deficiency, heavy metals, flooding, and other stresses, highlighting the need for further research in these areas.

The effect of nitrosative stress on histone H3 and H4 acetylation in Phytophthora infestans life cycle

The oomycete Phytophthora infestans is one of the most destructive phytopathogens globally. It has a proven ability to adapt to changing environments rapidly; however, molecular mechanisms responsible for host invasion and adaptation to new environmental conditions still need to be explored. The study aims to understand the epigenetic mechanisms exploited by P. infestans in response to nitrosative stress conditions created by the (micro)environment and the host plant. To characterize reactive nitrogen species (RNS)-dependent acetylation profiles in avirulent/virulent (avr/vr) P. infestans, a transient gene expression, ChIP and immunoblot analyses, and nitric oxide (NO) emission by chemiluminescence were used in combination with the pharmacological approach. Nitrosative stress increased total H3/H4 acetylation and some histone acetylation marks, mainly in sporulating hyphae of diverse (avr/vr) isolates and during potato colonization. These results correlated with transcriptional up-regulation of acetyltransferases PifHAC3 and PifHAM1, catalyzing H3K56 and H4K16 acetylation, respectively. NO or peroxynitrite–mediated changes were also associated with H3K56 and H4K16 mark deposition on the critical pathogenicity-related gene promoters (CesA1, CesA2, CesA3, sPLD-like1, Hmp1, and Avr3a) elevating their expression. Our study highlights RNS-dependent transcriptional reprogramming via histone acetylation of essential gene expression in the sporulating and biotrophic phases of plant colonization by P. infestans as a tool promoting its evolutionary plasticity.

Specialists regulate microbial network and community assembly in subtropical seagrass sediments under differing land use conditions

Microorganisms in the sediment play a pivotal role in the functioning and stability of seagrass ecosystems and their dynamics are influenced by the nutrient acquisition strategies of host plants. While the distinct impacts of microbial generalists and specialists on community dynamics are recognized, their distribution patterns and ecological roles within seagrass ecosystems remain largely unexplored. To address this issue, we conducted an analysis of community assembly processes and co-occurrence relationships of both microbial generalists and specialists within sediment profiles (0–100 cm) from seagrass habitats subjected to differing land use conditions. The results revealed that seagrasses in Yifeng Estuary experienced the large proportion of cultivated land and exhibited higher organic carbon content in the 0–20 cm surface sediment layer. Nitrogen-cycling bacteria were predominantly associated with seagrasses from Yifeng Estuary, whereas Vibrio spp. was more prevalent in seagrasses from Liusha Bay. Notably, seagrass Halophia beccarii (YHB) in Yifeng Estuary harbored higher niche breadths for both microbial generalist and specialist compared to Halodule uninervis (LHU) and Halophia ovalis (LHO) from Liusha Bay. Stochastic processes were pivotal in shaping seagrass sediment microbial communities, with a higher immigration rate observed in YHB, suggesting greater microbial turnover in this area. Additionally, YHB sediment presented lower drift and higher dispersal limitation among generalists compared to LHU and LHO, whereas the pattern was reversed among specialists. Specialists were found to play a crucial role in shaping microbial interactions within YHB sediment, with genera Halioglobus identified as keystone species in the network. The specialists were further found to significantly influence microbial β-diversity in seagrass sediment directly. Overall, our findings illustrated how microbial generalists and specialists were distributed in seagrass sediments in response to land use changes and provided new insights into the potential roles of microbial regulation in degraded seagrass ecosystems.

Mechanistic insights to Paenibacillus lentimorbus mediated biocontrol of Alternaria solani in Solanum lycopersicum L. through carbohydrate reallocation and sweet immunity suppression

Researchers envisaged that PGPR (plant growth promoting rhizobacteria) has vast possibilities as a bioinoculant that will lead to revolution. However, it's still very far from becoming commercially successful. Here, the information regarding the root colonization of PGPR in host plants and plant response towards PGPR is inadequate. It can provide valuable information for developing successful biofertilizers and biocontrol agents. PGPR (Paenibacillus lentimorbus NRRL B-30488 or CHM12) has been previously reported as a successful commercial biofertilizer and biocontrol agent. However, the exact mechanism of plant growth promotion and biocontrol is poorly studied. So, CHM12 was appraised for biotic stress amelioration of pathogen Alternaria solani in Tomato (Solanum lycopersicum L.) var. S-22 plants. PGPR CHM12 was assessed for various plant growth parameters such as proline, sugar content, etc. in pathogen A. solani (AS) challenged plants and compared with the CHM12 treated plants in a greenhouse study. Then, the metabolomics tool (GC-MS) was used to identify metabolites and their respective genes playing pivotal roles in colonization tactics availed by PGPR. Further, gene expression analysis was done to affirm the involvement of various genes related to metabolites providing biotic stress tolerance in Tomato plants. The current research discerned that PGPR CHM12 revealed significant differences in different plant growth parameters studied. There were 33 distinct metabolites identified, which stipulated the involvement of carbohydrate metabolism mainly in combating biotic stress in this study. Thus, our study reconfirmed very few reported previous results through gene expression analysis, suggesting the downregulation of carbohydrate metabolism genes in PGPR-treated plants. This downregulation of carbohydrate genes might be the critical factor for suppressing the plant's immune response to gaining entry inside the host plant. This also helps in retaining and reallocating carbohydrates in plant cells to reduce pathogen proliferation.