Molecular Plant-Microbe Interactions

Phenylhydrazine (PHZ), a potent chemical causes toxicity on various tissues at various levels. Administration of phenylhydrazine mainly causes haematotoxicity which leads to the haemolytic anemia. In mammals PHZ induced anemia increased the iron absorption in spleen, liver and duodenum and finally iron metabolism was altered. Local demand and supply of Fe would increase erythropoeitic activity of the spleen so the size of spleen was increased that create the splenomegaly. PHZ induced anemia activate immune response which triggers phagocytosis in the spleen and liver. Apart from this administration of PHZ interfere the binding of erythropoietin (EPO) with erythropoietin receptors (EPOR) so that JAK-STAT would be affected.PHZ also showed genotoxic effect by creating single strand DNA damage.

One of the major issues facing humankind is global food security. A changing climate, coupled with a heightened consumer awareness of how food is produced and legislative changes governing the usage of agrichemicals for improving plant health and yield, means that alternative, more integrated and sustainable approaches are needed for crop management practices. To this end, there is increasing recognition of the value of the role of microbial inoculants in agriculture. The focus of this review is to understand how plant-growth-promoting bacteria and arbuscular mycorrhizal fungi can play a part in improving crop yield by promoting the health status of the plant through the sequestration of various nutrients and in the control of plant diseases.

Laporan Praktikum Disusun oleh Emil Rahim, Prodi Agroteknologi, fakultas Pertanian, Universitas Jenderal Soedirman. Laporan praktikum mata kuliah Mikrobiologi Pertanian. Terdiri atas 14  acara diantaranya :
1. Acara I mengenai Pengenalan Alat.
2. Acara II mengenai Kalibrasi mikrometer Okuler dan Pengukuran Sel.
3. Acara III mengenai Pembuatan Media dan Pembuktian bahwa mikroba ada diudara.
4. Acara IV mengenai Sterilisasi dan Kerja Aseptis.
5. Acara V mengenai Isolasi Mikroba Rhizosfer.
6. Acara VI mengenai Metode pendugaan Jumlah Mikroba.
7. Acara VII mengenai Morfologi Koloni Mikroba.
8. Acara VIII mengenai Pewranaan Sel Bakteri.
9. Acara IX mengenai Inokulasi Rhizobium pada Benih kedelai.
10. Acara X mengenai Evaluasi Bintil Akar.
11. Acara XI mengenai Inokulasi Mikoriza pada Jagung, Penanaman, Pemeliharaan tanaman Jagung.
12. Acara XII mengenai Perhitungan Infeksi Mikoriza pada Akar jagung.
13. Acara XIII mengenai Pembuatan Pupuk Organik Cair (POC).
14. Acara XIV mengenai Pembuatan Biopestisida

Plants and microbes are co-evolved and interact with each other in nature. Plant-associated microbes, often referred to as plant microbiota, are an integral part of plant life. Depending on the health effects on hosts, plant-microbe (PM) interactions are either beneficial or harmful. The role of microbiota in plant growth promotion (PGP) and protection against various stresses is well known. Recently, our knowledge of community composition of plant microbiome and significant driving factors have significantly improved. So, the use of plant microbiome is a reliable approach for a next green revolution and to meet the global food demand in sustainable and eco-friendly agriculture. An application of the multifaceted PM interactions needs the use of novel tools to know critical genetic and molecular aspects. Recently discovered clustered regularly interspaced short palindromic repeats (CRISPR)/Cas-mediated genome editing (GE) tools are of great interest to explore PM interactions. A systematic understanding of the PM interactions will enable the application of GE tools to enhance the capacity of microbes or plants for agronomic trait improvement. This review focuses on applying GE techniques in plants or associated microbiota for discovering the fundamentals of the PM interactions, disease resistance, PGP activity, and future implications in agriculture.

This chapter will look forward at different types of microorganism’s interaction
with Plants. It will also discuss the effects which will arise after the interaction of microbes
with plants. Plant-Microbe Interactions Encounters between plant cells and both
‘friendly’ and ‘hostile’ microbes (such as those in symbiotic and pathogenic interactions,
respectively) trigger a range of highly dynamic plant cellular responses. Densely
colonized soil contains beneficial mycorrhizal fungi and rhizobia, which associate
with roots and provide plants with mineral nutrients and fixed nitrogen, respectively,
in exchange for carbon. By contrast, plants are constantly exposed to a range of
fungal, bacterial and viral pathogens, and have evolved unique defense mechanisms
to fight these infections. These include reorganization of the cytoskeleton, organelle
translocation, vesicle trafficking, and alterations in subcellular protein localization. Recent
progress in this border-land that bridges the fields of plant–microbe interactions
and cell biology heralds the transition from descriptive phenomenology to
the identification and characterization of key molecules that are involved in these
processes. Intriguingly, molecular events that occur in plant cells in response to
microbes also take place upon abiotic wounding and during fundamental plant
developmental processes, such as the tip growth of pollen, root hairs and trichomes.
Thus, elementary ‘activity modules’ that are required for the generation of cell polarity
in plant morphogenesis appear to be re-used in both abiotic and biotic stress
response pathways.

Global food security is vulnerable due to massive growth of the human population, changes in global climate, the emergence of novel/more virulent pathogens, and demands from increasingly discerning consumers for chemical-free, sustainably produced food products. Bacterium- based biological control agents (BCAs), if used as part of an integrated management system, may satisfy the above demands. We focus on the advantages, limitations, problems, and challenges involved in such strategies.

Biopharmaceutical companies have focused the development of recombinant proteins on bacteria, insect and mammalian cell platforms. The associated high cost with current biopharmaceutical manufacturing processes makes many therapies unattainable. Within the past few years, the development of deconstructed viral vectors based on transient expression systems has given credence to plants as a viable biofactory to express recombinant proteins. Plant molecular farming with agroinfiltration using tailored viral vectors allows for major advantages over standard production schemes including cost, scalability, safety, speed and yield. This review focuses on the developmental path of plant molecular farming culminating in today's revolutionary breakthroughs involving deconstructed vectors, Agrobacterium tumefaciens and diverse delivery platforms.

Variability among 44 isolates of Fusarium spp. the Chilli wilt pathogen, collected from different locations of south India was studied in respect of Cultural and morphological and pathogenic variability. The colony diameter ranged from 60 mm to 90 mm after 8 days of inoculation incubated at 27±1°C. The colony colour varied from white, cream and violet with yellow coloured pigmentation on Potato dextrose agar. The growth on different solid media revealed that the best media was Potato dextrose agar (90 mm) with abundant sporulation followed by oat meal agar and V-8 juice agar. The colour of the colony also varied from white, cottony, cream and greyish in different media. As for the pathogenic variability is concerned the isolates showed variations in causing disease in different varieties of chilli and these isolates were clustered into three groups based the disease reaction.

An autoactive chimera of the tomato extracellular leucine-rich repeat receptor-like protein Cf-9, designated Hcr9-M205 has been characterized previously as exhibiting characteristics of constitutive defence activation (Barker et al., 2006b). The initial work of this thesis (Chapter 3) involved generation and assessment of transgenic tobacco containing an E22 (PR-5) promoter: gusA reporter construct as a quantitative reporter for Hcr9-M205 autoactivity in Agrobacterium-mediated transient expression (agroinfiltration) assays. Time course analysis showed that the induction of E22 promoter preceded the necrotic response induced by Hcr9-M205, providing an early indication of defence activation. Further characterization of the E22 promoter (Chapter 4) by incubating the E22: gusA tobacco leaf disks in different defence-inducing compounds using a multi-well plate set-up indicated the defence-inducible nature of E22 promoter including antagonistic regulation by salicylic acid and jasmonic acid, activation by ethylene and synergistic activation by salicylic acid and cytokinin; demonstrating the applicability of the leaf disks assays in screening potential plant defence activators. Chapter 5 presents the structure-function analysis of the Hcr9-M205 protein. Previously, domain swapping analysis identified key regions involved in the control of Hcr9-M205 autoactivity namely a mismatch between LRRs 10-17 of Hcr9-9A (an upstream Cf-9 paralogue) and Cf-9 LRR 18 required for basal level of autoactivity and an additional Cf-9 C-terminal region comprising the loop-out domain and LRRs 24-26 for complete level of autoactivity (Anderson et al. in preparation). This thesis focuses on the proposed signalling repression domain in LRRs 10-17. Domain swapping analysis

Several plants of Catharanthus roseus cv 'leafless inflorescence (lli)' showing phenotype of phytoplasma infection were observed for symptoms of early flowering, virescence, phyllody, and apical clustering of branches. Symptomatic plants were studied for the presence/absence and identity of phytoplasma in flowers. Transcription levels of several genes involved in plants' metabolism and development, accumulation of pharmaceutically important terpenoid indole alkaloids in flowers and leaves and variation in the rootassociated microbial flora were examined. The expression profile of 12 genes studied was semi-quantitatively similar in control leaves and phytoplasma-infected leaves and flowers, in agreement with the symptoms of virescence and phyllody in phytoplasma-infected plants. The flowers of phytoplasma-infected plants possessed the TIA profile of leaves and accumulated catharanthine, vindoline, and vincristine and vinblastine in higher concentrations than leaves. The roots of the infected plants displayed lower microbial diversity than those of normal plants. In conclusion, phytoplasma affected the biology of C. roseus lli plants multifariously, it reduced the differences between the metabolite accumulates of the leaves and flowers and restrict the microbial diversity of rhizosphere.

Nicotiana benthamiana is the most widely used experimental host in plant virology, due mainly to the large number of diverse plant viruses that can successfully infect it. Additionally, N. benthamiana is susceptible to a wide variety of other plant-pathogenic agents (such as bacteria, oomycetes, fungi, and so on), making this species a cornerstone of host-pathogen research, particularly in the context of innate immunity and defense signaling. Moreover, because it can be genetically transformed and regenerated with good efficiency and is amenable to facile methods for virusinduced gene silencing or transient protein expression, N. benthamiana is rapidly gaining popularity in plant biology, particularly in studies requiring protein localization, interaction, or plant-based systems for protein expression and purification. Paradoxically, despite being an indispensable research model, little is known about the origins, genetic variation, or ecology of the N. benthamiana accessions currently used by the research community. In addition to addressing these latter topics, the purpose of this review is to provide information regarding sources for tools and reagents that can be used to support research in N. benthamiana. Finally, we propose that N. benthamiana is well situated to become a premier plant cell biology model, particularly for the virology community, who as a group were the first to recognize the potential of this unique Australian native.

Endophytes are omnipresent colonizers persist in the inner plant tissues where
they do not normally cause any considerable morphological changes and disease symptoms.
The term endophytes generally used for particular group of host and microbes
(‘Indo’-Living in ‘Phyco’- Plants). Mainly fungi and various bacteria comprises the
important group of endophytes. In general, an endophyte can be defined as a microorganism,
typically bacterial or fungal, that lives asymptomatically within a plant, causing
no signs of harm to the host (Bacon and White, 2000). Majority of the endophytes
colonize different compartments of the plant apoplast, including the intercellular spaces
of the cell walls and xylem vessels. Some of them are able to colonize reproductive
organs of plants, e.g. flowers, fruits and seeds.

Sclerotinia sclerotiorum is a necrotrophic, omnivorous plant pathogen with worldwide distribution. Sclerotia of S. sclerotiorum are pigmented, multihyphal structures that play a central role in the life and infection cycles of this pathogen. Calcineurin, a Ser/Thr phosphatase linked to several signal-transduction pathways, plays a key role in the regulation of cation homeostasis, morphogenesis, cellwall integrity, and pathogenesis in fungi. We demonstrate that calcineurin expression in S. sclerotiorum is altered in a phase-specific manner during sclerotial development. Inhibition of calcineurin by FK506, cysclosporin A, or inducible antisense calcineurin expression impaired sclerotial development at the prematuration phase and increased germination of preformed sclerotia. Induction of antisense calcineurin expression in S. sclerotiorum resulted in reduced pathogenesis on tomato and Arabidopsis. However, secretion of oxalic acid, a key virulence factor of S. sclerotiorum, was not altered. Inhibition of calcineurin conferred a reduction in cell wall β-1,3-glucan content and increased sensitivity to cell-wall-degrading enzymes and to the glucan synthase inhibitor caspofungin. Thus, calcineurin plays a major role in both sclerotial development and pathogenesis of S. sclerotiorum and, most likely, other phytopathogens.

The density and viscosity of solutions of methanol, ethanol, glucose and sucrose in distilled water at various temperatures were reported and compared with the available literature data. Data obtained was used to understand the interactions of substrates in solution. Influence of concentration of substrates and salts on strengthening or weakening of these interactions was evaluated. Apparent molar volumes were estimated from
density data of different systems. The presence of various polar groups in the molecules showed varying interactions and there by the viscosity also varies. The results reveal that the molecular interactions strongly depend on the polarity and the substituents attached to the hydroxyl groups. Influence of nature of substrates and the other ions commonly present in water is discussed. Also, we have analyzed the relations between alcohols and their properties using a data analysis technique, Formal Concept Analysis (FCA).

It has been reported that salicylic acid (SA) induces both immediate spike and long lasting phases of oxidative burst represented by the generation of reactive oxygen species (ROS) such as superoxide anion radical (O2
-). In general, in the earlier phase of oxidative burst, apoplastic peroxidase are likely involved and in the late phase of the oxidative burst, NADPH oxidase is likely involved. Key signaling events connecting the 2 phases of oxidative burst are calcium channel activation and protein phosphorylation events. To date, the known earliest signaling event in response to exogenously added SA is the cell wall peroxidase-catalyzed generation of O2
- in a hydrogen peroxide (H2O2)-dependent manner. However, this model is incomplete since the source of the initially required H2O2 could not be explained. Based on the recently proposed role for H2O2-independent mechanism for ROS production catalyzed by plant peroxidases (Kimura et al., 2014, Frontiers in Plant Science), we hereby propose a novel model for plant peroxidase-catalyzed oxidative burst fueled by SA.

The type III secretion system (TTSS) is a specialized protein secretion machinery used by numerous gram-negative bacterial pathogens of animals and plants to deliver effector proteins directly into the host cells. In plant-pathogenic bacteria, genes encoding the TTSS were discovered as hypersensitive response and pathogenicity (hrp) genes, because mutation of these genes typically disrupts the bacterial ability to cause diseases on host plants and to elicit hypersensitive response on nonhost plants. The hrp genes and the type III effector genes (collectively called TTSS genes hereafter) are repressed in nutrient-rich media but induced when bacteria are infiltrated into plants or incubated in nutrient-deficient inducing media. Multiple regulatory components have been identified in the plant-pathogenic bacteria regulating TTSS genes under various conditions. In Ralstonia solanacearum, several signal transduction components essential for the induction of TTSS genes in plants are dispensable for the induction in inducing medium. In addition to the inducing signals, recent studies indicated the presence of negative signals in the plant regulating the Pseudomonas syringae TTSS genes. Thus, the levels of TTSS gene expression in plants likely are determined by the interactions of multiple signal transduction pathways. Studies of the hrp regulons indicated that TTSS genes are coordinately regulated with a number of non-TTSS genes.

Plant growth promoting rhizobacteria (PGPR) impact the root morphogenesis and subsequently modify the root system architecture of a plant. This study was conducted to assess the early modifications of rice root architecture by a PGPR strain, Bacillus altitudinis (strain FD48). Rice seedlings grown in culture tubes under gnoto-biotic conditions were inoculated with FD48, and root architecture variables of growing roots were measured in a nondestructive manner using 2-dimensional imaging and processing at periodic intervals. Among the twenty root architecture variables pulled out from the image analysis, the variables such as maximum number of roots, number of lateral roots, root thickness, area, volume and bushiness were significantly increased with time course due to PGPR inoculation than uninoculated control. Specific root length, root depth and length distribution were negatively impacted by PGPR. FD48 inoculation regulated the indole-3-acetic acid accumulation in rice root as compared to uninoculated control. To validate the hormonal modulation leading the root phenotypic modification , the expression of auxin-responsive genes (AUX/IAA) of rice were assessed by reverse transcriptase quantitative PCR. The time course expression pattern of the genes responsible for shortening of primary roots (OsIAA1 and OsIAA4) and genes for lateral root formation (OsIAA11 and OsIAA13) were modulated by PGPR inoculation. These results demonstrate that PGPR play a major role in controlling endogenous IAA levels in rice roots by regulating the auxin-responsive genes and thereby cause changes in root architecture of rice.

We have initiated studies on the molecular biology and genetics of white sweetclover (Melilotus alba Desr.) and its responses to inoculation with the nitrogen-fixing symbiont Sinorhizobium meliloti. Early nodulin genes such as ENOD40 serve as markers for the transition from root to nodule development even before visible stages of nodule formation are evident. Using Northern blot analysis, we found that the ENOD40 gene was expressed within 6 h after inoculation with two different strains of S. meliloti, one of which overproduces symbiotic Nod factors. Inoculation with this strain resulted in an additional increase in ENOD40 gene expression over a typical wild-type S. meliloti strain. Moreover, the increase in mRNA brought about by the Nod-factor-overproducing strain 24 h after inoculation was correlated with lateral root formation by using whole-mount in situ hybridization to localize ENOD40 transcripts in lateral root meristems and by counting lateral root initiation sites. Cortical cell divisions were not detected. We also found that nodulation occurred more rapidly on white sweetclover in response to the Nod-factor-overproducing strain, but ultimately there was no difference in nodulation efficiency in terms of nodule number or the number of roots nodulated by the two strains. Also, the two strains could effectively co-colonize the host when inoculated together, although a few host cells were occupied by both strains.

Food security (a pressing issue for all nations) faces a threat due to population growth, land availability for growing crops, a changing climate (leading to increases in both abiotic and biotic stresses), heightened consumer awareness of the risks related to the use of agrichemicals, and also the reliance on depleting fossil fuel reserves for their production. Legislative changes in Europe mean that fewer agrichemicals will be available in the future for the control of crop pests and pathogens. The need for the implementation of a more sustainable
agricultural system globally, incorporating an integrated approach to disease management, has never been more urgent. To that end, the Valorizing Andean Microbial Diversity (VALORAM) project (http://valoram.ucc.ie), funded under FP7, examined the role of microbial
communities in crop production and protection to improve the sustainability, food security, environmental protection, and productivity for rural Andean farmers. During this work, microbial volatile organic compounds (mVOCs) of 27 rhizobacterial isolates were identified using gas chromatography/mass spectrometry (GC/MS), and their antifungal
activity against Rhizoctonia solani was determined in vitro and compared to the activity of a selection of pure volatile compounds. Five of these isolates, Pseudomonas palleroniana R43631, Bacillus sp. R47065, R47131, Paenibacillus sp. B3a R49541, and Bacillus simplex M3-4 R49538 trialled in the field in their respective countries of origin, i.e., Bolivia, Peru, and Ecuador, showed significant increase in the yield of potato. The strategy followed in the VALORAM project may offer a template for the future isolation and determination of putative biocontrol and plant growth-promoting agents, useful as part of a low-input integrated pest management system.

Work on the interaction of aerial plant parts with pathogens has identified the signaling molecules jasmonic acid (JA) and salicylic acid (SA) as important players in induced defense of the plant against invading organisms. Much less is known about the role of JA and SA signaling in root infection. Recent progress has been made in research on plant interactions with biotrophic mutualists and parasites that exclusively associate with roots, namely arbuscular mycorrhizal and rhizobial symbioses on one hand and nematode and parasitic plant interactions on the other hand. Here, we review these recent advances relating JA and SA signaling to specific stages of root colonization and discuss how both signaling molecules contribute to a balance between compatibility and defense in mutualistic as well as parasitic biotroph-root interactions.

Because rare earth elements (REEs) are not present at high concentrations in the normal environments surrounding living organisms, the biological roles of REEs had not been intensively tested to date. In this article, the ongoing studies on the biology and biochemistry of REEs applied to growing plants and plant cells are reviewed.

The heterotrimeric G proteins and mitogen-activated protein kinases (MAPKs) conserved signaling pathways are involved in the development, reproduction and pathogenicity in filamentous fungi. The two-component histidine kinase, known also as the HOG MAPK pathway, regulates a similar complex set of responses and is known to mediate the phenylpyrrole fludioxonil fungicide response in fungi. We used Cochliobolus heterostrophus mutant strains deficient in G-protein α (cga1) and/or β (cgb1) subunits or MAPK (chk1, mps1 and hog1) to uncover their role in the mediation of this fungicide’s activity and resistance. The results revealed complex interactions between the G-protein subunits and the MAPK in response to osmotic/ionic and fludioxonil stresses. Under normal conditions, the Hog1 pathway restricts glycerol accumulation since its disruption leads to hyperosmosensitivity and very high cellular glycerol accumulation. The hog1 mutants were also relatively resistance to fludioxonil. Moreover, our results suggest that cgb1, chk1 and mps1 are also weak repressors of this response since mutation in these genes caused relatively high elevation in glycerol levels in the cells. Supporting this is the finding that these three strains exhibit resistance to KCl stress. In contrast, the cga1 strain has only moderate levels of cellular glycerol (higher than those of the wild type, but lower than those of the other mutants) that are little affected by KCl or fludioxonil stress. Indeed, these mutants are highly sensitive to KCl stress. This suggests that Cga1 is a moderate repressor of cellular glycerol under normal conditions and an enhancer of glycerol accumulation under osmotic/ionic stress conditions. Together these findings reveals that the sensitivity to fludioxonil is not only positively controlled by the Hog1 pathway, but also mediated by the Chk1, Mps1, Cga1 and Cgb1 pathways. This study provides insight into the roles of G-protein in mediating the anti-fungal fludioxonil response. A model is proposed for the interactions between the G-protein and MAPK signaling pathways.

The regulation of expression of the two virion-sense (V1 and V2) and four complementary-sense (C1, C2, C3, and C4) open reading frames (ORFs) of Tomato leaf curl virus (TLCV) was studied in both stably and transiently transformed Nicotiana tabacum tissues with fusions with the βglucuronidase (GUS) reporter gene. GUS-expressing transgenic lines were obtained with each of the four complementary-sense gene-GUS fusion constructs and with truncated versions of the virion-sense gene-GUS fusion constructs (V1GUS∆C and V2GUS∆C) lacking complementary-sense sequences encoding the C1, C2, and C3 ORFs. However, little or no GUS expression was observed in kanamycin-resistant plants transformed with fulllength, virion-sense gene constructs (V1GUS and V2GUS) constituting the complete viral genome. In contrast, V1GUS and V2GUS were found to direct high-level GUS expression in transient assays with tobacco protoplasts, suggesting that integration of viral constructs containing functional, complementary-sense genes may lead to repression or deletion of the introduced constructs in transgenic tissues. V2GUS expression in the transient protoplast assay was found to be severely curtailed by specific mutation of the C2 ORF, supporting a role for the C2 protein in transactivation of TLCV virion-sense gene expression. TLCV ORF-GUS constructs displayed distinctive tissue expression patterns in transgenic tobacco plants that could be divided into constitutive (C1, C4, and V2GUS∆C), predominantly vascular (C2, C3), or reduced expression in cells associated with the vascular bundles (V1GUS∆C). The significance of these results is discussed in terms of current models of gene function and regulation in geminiviruses.

Delivery into plants of T-DNAs containing promoter, terminator, or coding sequences generated small interfering RNAs (siRNAs) specific to each type of sequence. When both promoter and transcribed sequences were simultaneously present in the T-DNA, accumulation of siRNAs to transcribed sequences was favored over accumulation of siRNAs to the nontranscribed upstream promoter sequences. The generation of specific siRNA sequences occurred even in the absence of T-DNA homology to sequences in the plant. Delivery of T-DNA, with homology to the transgene limited to the nontranscribed cauliflower mosaic virus 35S promoter (35SP) and the transcribed nopaline synthase transcription termination (NosT)signal sequences, into transgenic plants expressing the green fluorescent protein (GFP), generated siRNAs in infiltrated tissues to both 35SP (35SsiRNAs) and NosT (NosTsiRNAs), but not to the GFP sequence (GFPsiRNAs). In infiltrated tissues, the 35SsiRNAs failed to trigger the transcriptional sile...

The tomato gene Mi-1.2 confers resistance against root-knot nematodes and some isolates of potato aphid. Resis-tance to the whitefly Bemisia tabaci previously has been ob-served in Mi-bearing commercial tomato cultivars, suggest-ing that Mi, or a closely linked gene, is ...

In legume–rhizobia symbiosis, Ca2+/calmodulin-dependent protein kinase (CCaMK) is essential for rhizobial invasion through infection threads in the epidermis and nodule organogenesis in the cortex. Though CCaMK is actively transcribed in the infected zone of nodules, its role in the later stages of nodule development remain elusive because of the epidermal arrest of “loss-of-function” mutants. In Aeschynomeneae legumes such as Arachis hypogea, rhizobia directly access the cortex, where nodule organogenesis as well as endosymbiont dissemination take place by multiplication of infected cortical cells. We characterized CCaMK (GI:195542474) from A. hypogea and downregulated the kinase through RNA interference (RNAi) to understand its role during organogenesis of its characteristic aeschynomenoid nodules. In CCaMK downregulated plants, the inception of nodules was delayed by approximately 4 weeks and nodulation capacity was decreased (>90%). The infected zones of the RNA interference ...

Colonization of plant rhizosphere/roots by beneficial microorganisms (e.g. plant growth promoting rhizobacteria – PGPR, arbuscular mycorrhizal fungi – AMF) confers broad-spectrum resistance to virulent pathogens and is known as induced systemic resistance (ISR) and mycorrhizal-induced resistance (MIR). ISR or MIR, an indirect mechanism for biocontrol, involves complex signaling networks that are regulated by several plant hormones, the most important of which are salicylic acid (SA), jasmonic acid (JA) and ethylene (ET). In the present study, we investigated if inoculation of potato plantlets with an AMF (Rhizophagus irregularis MUCL 41833) and a PGPR (Pseudomonas sp R41805) either alone or in combination, could elicit host defense response genes in the presence or absence of Rhizoctonia Solani EC-1, a major potato pathogen. RT-qPCR revealed the significant expression of ethylene response factor 3 (EFR3) in mycorrhized potato plantlets inoculated with Pseudomonas sp R41805 and also in mycorrhized potato plantlets inoculated with Pseudomonas sp R41805 and challenged with R. solani. The significance of ethylene response factors (ERFs) in pathogen defense has been well documented in the literature. The results of the present study suggest that the dual inoculation of potato with PGPR and AMF may play a part in the activation of plant systemic defense systems via ERF3.

Antagonistic coevolution between plants and pathogens has generated a broad array of attack and defense mechanisms. In the classical avirulence (Avr) gene-for-gene model, the pathogen gene evolves to escape host recognition while the host resistance (R) gene evolves to track the evolving pathogen elicitor. In the case of host-specific toxins (HST), the evolutionary arms race may be inverted, with the gene encoding the pathogen toxin evolving to maintain recognition of the host sensitivity target while the host sensitivity gene evolves to escape binding with the toxin. Pathogen effector genes, including those encoding Avr elicitors and HST, often show elevated levels of polymorphism reflecting the coevolutionary arms race between host and pathogen. However, selection can also eliminate variation in the coevolved gene and its neighboring regions when advantageous alleles are swept to fixation. The distribution and diversity of corresponding host genes will have a major impact on the distribution and diversity of effectors in the pathogen population. Population genetic analyses including both hosts and their pathogens provide an essential tool to understand the diversity and dynamics of effector genes. Here, we summarize current knowledge about the population genetics of fungal and oomycete effector genes, focusing on recent studies that have used both spatial and temporal collections to assess the diversity and distribution of alleles and to monitor changes in allele frequencies over time. These studies illustrate that effector genes exhibit a significant degree of diversity at both small and large sampling scales, suggesting that local selection plays an important role in their evolution. They also illustrate that Avr elicitors and HST may be recognizing the same R genes in plants, leading to evolutionary outcomes that differ for necrotrophs and biotrophs while affecting the evolution of the corresponding R genes. Under this scenario, the optimal number of R genes in a plant genome may be determined by the relative abundance of necrotrophic and biotrophic pathogens in the plant's environment.

In Rhizobium etli CFN42, both the symbiotic plasmid (pd) and plasmid b (pb) are required for effective bean nodulation. This is due to the presence on pb of a region (lpsβ) involved in lipopolysaccharide (LPS) biosynthesis. We report here the genetic array and functional features of this plasmid-borne region. The sequence analysis of a 3,595-bp fragment revealed the presence of a transcriptional unit integrated by two open reading frames (lpsβ1 and lpsβ2) essential for LPS biosynthesis and symbiosis. The lpsβ1 encodes a putative 193 amino acid polypeptide that shows strong homology with glucosyl-1P and galactosyl-1P transferases. The deduced amino acid sequence of the protein encoded by lpsβ2 was very similar to that of proteins involved in surface polysaccharide biosynthesis, such as Pseudomonas aeruginosa WpbM, Bordetella pertussis BplL, and Yersinia enterocolitica TrsG. DNA sequences homologous to lpsβ1 and lpsβ2 of R. etli CFN42 were consistently found in functionally equivalent plasmids of R. etli, R. leguminosarum bv. viciae, and R. leguminosarum bv. trifolii strains, but not in R. meliloti, R. loti, R. tropici, R. fredii, Bradyrhizobium, Azorhizobium, and Agrobacterium tumefaciens. Even though Rhizobium and Agrobacterium do not share lpsβ sequences, their presence is required for crown-gall tumor induction by R. etli transconjugants carrying the Ti plasmid.

Ethylene response factor 1 (ERF1) is a transcriptional factor from Arabidopsis thaliana that regulates plant resistance to the necrotrophic fungi Botrytis cinerea and Plectosphaerella cucumerina and whose overexpression enhances resistance to these fungi. Here, we show that ERF1 also mediates Arabidopsis resistance to the soilborne fungi Fusarium oxysporum sp. conglutinans and F. oxysporum f. sp. lycopersici, because its constitutive expression in Arabidopsis confers enhanced resistance to these pathogens. Expression of ERF1 was upregulated after inoculation with F. oxysporum f. sp. conglutinans, and this response was blocked in ein2-5 and coi1-1 mutants, impaired in the ethylene (ET) and jasmonic acid (JA) signal pathways, respectively, which further indicates that ERF1 is a downstream component of ET and JA defense responses. The signal transduction network controlling resistance to F. oxysporum fungi was explored using signalingdefective mutants in ET (ein2-5), JA (jar1-1), and salicylic acid (SA) transduction pathways. This analysis revealed that Arabidopsis resistance to F. oxysporum requires the ET, JA, and SA signaling pathways and the NPR1 gene, although it is independent of the PAD4 and EDS1 functions.

Plant processes resulting from primary or secondary metabolism have been hypothesized to contribute to defense against microbial attack. Barley chorismate synthase (HvCS), anthranilate synthase α subunit 2 (HvASa2), and chorismate mutase 1 (HvCM1) occupy pivotal branch points downstream of the shikimate pathway leading to the synthesis of aromatic amino acids. Here, we provide functional evidence that these genes contribute to penetration resistance to Blumeria graminis f. sp. hordei, the causal agent of powdery mildew disease. Single-cell transientinduced gene silencing of HvCS and HvCM1 in mildew resistance locus a (Mla) compromised cells resulted in increased susceptibility. Correspondingly, overexpression of HvCS, HvASa2, and HvCM1 in lines carrying mildew resistance locus o (Mlo), a negative regulator of penetration resistance, significantly decreased susceptibility. Barley stripe mosaic virus-induced gene silencing of HvCS, HvASa2, and HvCM1 significantly increased B. graminis f. sp. hordei penetration into epidermal cells, followed by formation of haustoria and secondary hyphae. However, sporulation of B. graminis f. sp. hordei was not detected on the silenced host plants up to 3 weeks after inoculation. Taken together, these results establish a previously unrecognized role for the influence of HvCS, HvASa2, and HvCM1 on penetration resistance and on the rate of B. graminis f. sp. hordei development in Mla-mediated, barley-powdery mildew interactions.

Pathogenicity mitogen-activated protein kinases (MAPKs), related to yeast FUS3/KSS1, are essential for virulence in fungi, including Cochliobolus heterostrophus, a necrotrophic pathogen causing Southern corn leaf blight. We compared the phenotypes of mutants in three MAPK genes: HOG1, MPS1, and CHK1. The chk1 and mps1 mutants show autolytic appearance, light pigmentation, and dramatic reduction in virulence and conidiation. Similarity of mps1 and chk1 mutants is reflected by coregulation by these two MAPKs of several genes. Unlike chk1, mps1 mutants are female-fertile and form normal-looking appressoria. HOG1 mediates resistance to hyperosmotic and, to a lesser extent, oxidative stress, and is required for stress upregulation of glycerol-3-phosphate phosphatase, transaldolase, and a monosaccharide transporter. Hog1, but not Mps1 or Chk1, was rapidly phosphorylated in response to increased osmolarity. The hog1 mutants have smaller appressoria and cause decreased disease symptoms on maize leaves. Surprisingly, loss of MPS1 in a wild-type or hog1 background improved resistance to some stresses. All three MAPKs contribute to the regulation of central developmental functions under normal and stress conditions, and full virulence cannot be achieved without appropriate input from all three pathways.