AvrRpm1 missense mutations weakly activate RPS2-mediated immune response in Arabidopsis thaliana

Diversified host target families mediate convergently evolved effector recognition across plant species

Recognition of pathogen effectors is a crucial step for triggering plant immunity. Resistance (R) genes often encode for nucleotide-binding leucine-rich repeat receptors (NLRs), and NLRs detect effectors from pathogens to trigger effector-triggered immunity (ETI). NLR recognition of effectors is observed in diverse forms where NLRs directly interact with effectors or indirectly detect effectors by monitoring host guardees/decoys (HGDs). HGDs undergo different biochemical modifications by diverse effectors and expand the effector recognition spectrum of NLRs, contributing robustness to plant immunity. Interestingly, in many cases of the indirect recognition of effectors, HGD families targeted by effectors are conserved across the plant species while NLRs are not. Notably, a family of diversified HGDs can activate multiple non-orthologous NLRs across plant species. Further investigation on HGDs would reveal the mechanistic basis of how the diversification of HGDs confers novel effector recognition by NLRs.

A conserved glutamate residue in RPM1-INTERACTING PROTEIN4 is ADP-ribosylated by the Pseudomonas effector AvrRpm2 to activate RPM1-mediated plant resistance

Gram-negative bacterial plant pathogens inject effectors into their hosts to hijack and manipulate metabolism, eluding surveillance at the battle frontier on the cell surface. The effector AvrRpm1Pma from Pseudomonas syringae pv. maculicola functions as an ADP-ribosyl transferase that modifies RESISTANCE TO P. SYRINGAE PV MACULICOLA1 (RPM1)-INTERACTING PROTEIN4 (RIN4), leading to the activation of Arabidopsis thaliana (Arabidopsis) resistance protein RPM1. Here we confirmed the ADP-ribosyl transferase activity of another bacterial effector, AvrRpm2Psa from P. syringae pv. actinidiae, via sequential inoculation of Pseudomonas strain Pto DC3000 harboring avrRpm2Psa following Agrobacterium-mediated transient expression of RIN4 in Nicotiana benthamiana. We conducted mutational analysis in combination with mass spectrometry to locate the target site in RIN4. A conserved glutamate residue (Glu156) is the most likely target for AvrRpm2Psa, as only Glu156 could be ADP-ribosylated to activate RPM1 among candidate target residues identified from the MS/MS fragmentation spectra. Soybean (Glycine max) and snap bean (Phaseolus vulgaris) RIN4 homologs without glutamate at the positions corresponding to Glu156 of Arabidopsis RIN4 are not ADP-ribosylated by bacterial AvrRpm2Psa. In contrast to the effector AvrB, AvrRpm2Psa does not require the phosphorylation of Thr166 in RIN4 to activate RPM1. Therefore, separate biochemical reactions by different pathogen effectors may trigger the activation of the same resistance protein via distinct modifications of RIN4.

Beauty and the pathogens: A leaf-less control presents a better image of Cymbidium orchids defense strategy

Biological control is a safe way of combating plant diseases using the living organisms. For the precise use of microbial biological control agents, the genetic information on the hypersensitive response (HR), and defense-related gene induction pathways of plants are necessary. Orchids are the most prominent stakeholders of floriculture industry, and owing to their long-awaited flowering pattern, disease control is imperative to allow healthy vegetative growth that spans more than 2 years in most of the orchids. We observed leaf-less flowering in three orchid species (Cymbidium ensifolium, C. goeringii and C. sinense). Using these materials as reference, we performed transcriptome profiling for healthy leaves from non-infected plants to identify genes specifically involved in plant-pathogen interaction pathway. For this pathway, a total of 253 differentially expressed genes (DEGs) were identified in C. ensifolium, 189 DEGs were identified in C. goeringii and 119 DEGs were found in C. sinense. These DEGs were mainly related to bacterial secretion systems, FLS2, CNGCs and EFR, regulating HR, stomatal closure and defense-related gene induction. FLS2 (LRR receptor-like serine/threonine kinase) contained the highest number of DEGs among three orchid species, followed by calmodulin. Highly upregulated gene sets were found in C. sinense as compared to other species. The great deal of DEGs, mainly the FLS2 and EFR families, related to defense and immunity responses can effectively direct the future of biological control of diseases for orchids.

Direct acetylation of a conserved threonine of RIN4 by the bacterial effector HopZ5 or AvrBsT activates RPM1-dependent immunity in Arabidopsis

Plant pathogenic bacteria deliver effectors into plant cells to suppress immunity and promote pathogen survival; however, these effectors can be recognized by plant disease resistance proteins to activate innate immunity. The bacterial acetyltransferase effectors HopZ5 and AvrBsT trigger immunity in Arabidopsis thaliana genotypes lacking SUPPRESSOR OF AVRBST-ELICITED RESISTANCE 1 (SOBER1). Using an Arabidopsis accession, Tscha-1, that naturally lacks functional SOBER1 but is unable to recognize HopZ5, we demonstrated that RESISTANCE TO P. SYRINGAE PV MACULICOLA 1 (RPM1) and RPM1-INTERACTING PROTEIN 4 (RIN4) are indispensable for HopZ5- or AvrBsT-triggered immunity. Remarkably, T166 of RIN4, the phosphorylation of which is induced by AvrB and AvrRpm1, is directly acetylated by HopZ5 and AvrBsT. Furthermore, we demonstrated that the acetylation of RIN4 T166 is required and sufficient for HopZ5- or AvrBsT-triggered RPM1-dependent defense activation. Finally, we showed that SOBER1 interferes with HopZ5- or AvrBsT-triggered immunity by deacetylating RIN4 T166. Collectively, our study elucidates detailed molecular mechanisms underlying the activation and suppression of plant innate immunity triggered by two bacterial acetyltransferases, HopZ5 and AvrBsT, from different bacterial pathogens.

The receptor-like cytoplasmic kinase CDG1 negatively regulates Arabidopsis pattern-triggered immunity and is involved in AvrRpm1-induced RIN4 phosphorylation

Arabidopsis CDG1 negatively regulates flg22- and chitin-triggered immunity by promoting FLS2 and CERK1 degradation and is partially required for bacterial effector AvrRpm1-induced RIN4 phosphorylation. Negative regulators play indispensable roles in pattern-triggered immunity in plants by preventing sustained immunity impeding growth. Here, we report Arabidopsis thaliana CONSTITUTIVE DIFFERENTIAL GROWTH1 (CDG1), a receptor-like cytoplasmic kinase VII member, as a negative regulator of bacterial flagellin/flg22- and fungal chitin-triggered immunity. CDG1 can interact with the flg22 receptor FLAGELLIN SENSITIVE2 (FLS2) and chitin co-receptor CHITIN ELICITOR RECEPTOR KINASE1 (CERK1). CDG1 overexpression impairs flg22 and chitin responses by promoting the degradation of FLS2 and CERK1. This process requires the kinase activity of MEK KINASE1 (MEKK1), but not the Plant U-Box (PUB) ubiquitin E3 ligases PUB12 and PUB13. Interestingly, the Pseudomonas syringae effector AvrRpm1 can induce CDG1 to interact with its host target RPM1-INTERACTING PROTEIN4 (RIN4), which depends on the ADP-ribosyl transferase activity of AvrRpm1. CDG1 is capable of phosphorylating RIN4 in vitro at multiple sites including Thr166 and the AvrRpm1-induced Thr166 phosphorylation of RIN4 is diminished in cdg1 null plants. Accordingly, CDG1 knockout attenuates AvrRpm1-induced hypersensitive response and increases the growth of AvrRpm1-secreting bacteria in plants. Unexpectedly, AvrRpm1 can also induce FLS2 depletion, which is fully dependent on RIN4 and partially dependent on CDG1, but does not require the kinase activity of MEKK1. Collectively, this study reveals previously unknown functions of CDG1 in both pattern-triggered immunity and effector-triggered susceptibility in plants.

What the Wild Things Do: Mechanisms of Plant Host Manipulation by Bacterial Type III-Secreted Effector Proteins

Phytopathogenic bacteria possess an arsenal of effector proteins that enable them to subvert host recognition and manipulate the host to promote pathogen fitness. The type III secretion system (T3SS) delivers type III-secreted effector proteins (T3SEs) from bacterial pathogens such as Pseudomonas syringae, Ralstonia solanacearum, and various Xanthomonas species. These T3SEs interact with and modify a range of intracellular host targets to alter their activity and thereby attenuate host immune signaling. Pathogens have evolved T3SEs with diverse biochemical activities, which can be difficult to predict in the absence of structural data. Interestingly, several T3SEs are activated following injection into the host cell. Here, we review T3SEs with documented enzymatic activities, as well as T3SEs that facilitate virulence-promoting processes either indirectly or through non-enzymatic mechanisms. We discuss the mechanisms by which T3SEs are activated in the cell, as well as how T3SEs modify host targets to promote virulence or trigger immunity. These mechanisms may suggest common enzymatic activities and convergent targets that could be manipulated to protect crop plants from infection.

Rpa1 mediates an immune response to avrRpm1Psa and confers resistance against Pseudomonas syringae pv. actinidiae

The type three effector AvrRpm1Pma from Pseudomonas syringae pv. maculicola (Pma) triggers an RPM1-mediated immune response linked to phosphorylation of RIN4 (RPM1-interacting protein 4) in Arabidopsis. However, the effector-resistance (R) gene interaction is not well established with different AvrRpm1 effectors from other pathovars. We investigated the AvrRpm1-triggered immune responses in Nicotiana species and isolated Rpa1 (Resistance to Pseudomonas syringae pv. actinidiae 1) via a reverse genetic screen in Nicotiana tabacum. Transient expression and gene silencing were performed in combination with co-immunoprecipitation and growth assays to investigate the specificity of interactions that lead to inhibition of pathogen growth. Two closely related AvrRpm1 effectors derived from Pseudomonas syringae pv. actinidiae biovar 3 (AvrRpm1Psa ) and Pseudomonas syringae pv. syringae strain B728a (AvrRpm1Psy ) trigger immune responses mediated by RPA1, a nucleotide-binding leucine-rich repeat protein with an N-terminal coiled-coil domain. In a display of contrasting specificities, RPA1 does not respond to AvrRpm1Pma , and correspondingly AvrRpm1Psa and AvrRpm1Psy do not trigger the RPM1-mediated response, demonstrating that separate R genes mediate specific immune responses to different AvrRpm1 effectors. AvrRpm1Psa co-immunoprecipitates with RPA1, and both proteins co-immunoprecipitate with RIN4. In contrast with RPM1, however, RPA1 was not activated by the phosphomimic RIN4T166D and silencing of RIN4 did not affect the RPA1 activity. Delivery of AvrRpm1Psa by Pseudomonas syringae pv. tomato (Pto) in combination with transient expression of Rpa1 resulted in inhibition of the pathogen growth in N. benthamiana. Psa growth was also inhibited by RPA1 in N. tabacum.

A host target of a bacterial cysteine protease virulence effector plays a key role in convergent evolution of plant innate immune system receptors

Some virulence effectors secreted from pathogens target host proteins and induce biochemical modifications that are monitored by nucleotide-binding and leucine-rich repeat (NLR) immune receptors. Arabidopsis RIN4 protein (AtRIN4: RPM1-interacting protein 4) homologs are present in diverse plant species and targeted by several bacterial type III effector proteins including the cysteine protease AvrRpt2. RIN4 is 'guarded' by several independently evolved NLRs from various plant species, including Arabidopsis RPS2. Recently, it was shown that the MR5 NLR from a wild apple relative can recognize the AvrRpt2 effector from Erwinia amylovora, but the details of this recognition remained unclear. The present contribution reports the mechanism of AvrRpt2 recognition by independently evolved NLRs, MR5 from apple and RPS2, both of which require proteolytically processed RIN4 for activation. It shows that the C-terminal cleaved product of apple RIN4 (MdRIN4) but not AtRIN4 is necessary and sufficient for MR5 activation. Additionally, two polymorphic residues in AtRIN4 and MdRIN4 are identified that are crucial in the regulation of and physical association with NLRs. It is proposed that polymorphisms in RIN4 from distantly related plant species allow it to remain an effector target while maintaining compatibility with multiple NLRs.

TaRPM1 Positively Regulates Wheat High-Temperature Seedling-Plant Resistance to Puccinia striiformis f. sp. tritici

RPM1 is a CC-NBS-LRR protein that was first shown to be required for resistance to Pseudomonas syringae pv. maculicola in Arabidopsis thaliana. Our previous study showed that TaRPM1 gene in wheat was upregulated about six times following infection by Puccinia striiformis f. sp. tritici (Pst) under high temperature, compared with normal temperature. To study the function of TaRPM1 in wheat high-temperature seedling-plant (HTSP) resistance to Pst, the full length of TaRPM1 was cloned, with three copies each located on chromosomes 1A, 1B, and 1D. Transient expression of the TaRPM1-GFP fusion protein in Nicotiana benthamiana indicated that TaRPM1 localizes in the cytoplasm and nucleus. Profiling TaRPM1 expression indicated that TaRPM1 transcription was rapidly upregulated upon Pst inoculation under high temperature. In addition, TaRPM1 was induced by exogenous salicylic acid hormone application. Silencing TaRPM1 in wheat cultivar Xiaoyan 6 (XY 6) resulted in reduced HTSP resistance to Pst in terms of reduced number of necrotic cells and increased uredinial length, whereas no obvious phenotypic changes were observed in TaRPM1-silenced leaves under normal temperature. Related defense genes TaPR1 and TaPR2 were downregulated in TaRPM1-silenced plants under high temperature. We conclude that TaRPM1 is involved in HTSP resistance to Pst in XY 6.

AvrRpm1 Functions as an ADP-Ribosyl Transferase to Modify NOI Domain-Containing Proteins, Including Arabidopsis and Soybean RPM1-Interacting Protein4

The Pseudomonas syringae effector protein AvrRpm1 activates the Arabidopsis (Arabidopsis thaliana) intracellular innate immune receptor protein RESISTANCE TO PSEUDOMONAS MACULICOLA1 (RPM1) via modification of a second Arabidopsis protein, RPM1-INTERACTING PROTEIN4 (AtRIN4). Prior work has shown that AvrRpm1 induces phosphorylation of AtRIN4, but homology modeling indicated that AvrRpm1 may be an ADP-ribosyl transferase. Here, we show that AvrRpm1 induces ADP-ribosylation of RIN4 proteins from both Arabidopsis and soybean (Glycine max) within two highly conserved nitrate-induced (NOI) domains. It also ADP ribosylates at least 10 additional Arabidopsis NOI domain-containing proteins. The ADP-ribosylation activity of AvrRpm1 is required for subsequent phosphorylation on Thr-166 of AtRIN4, an event that is necessary and sufficient for RPM1 activation. We also show that the C-terminal NOI domain of AtRIN4 interacts with the exocyst subunits EXO70B1, EXO70E1, EXO70E2, and EXO70F1. Mutation of either EXO70B1 or EXO70E2 inhibited secretion of callose induced by the bacterial flagellin-derived peptide flg22. Substitution of RIN4 Thr-166 with Asp enhanced the association of AtRIN4 with EXO70E2, which we posit inhibits its callose deposition function. Collectively, these data indicate that AvrRpm1 ADP-ribosyl transferase activity contributes to virulence by promoting phosphorylation of RIN4 Thr-166, which inhibits the secretion of defense compounds by promoting the inhibitory association of RIN4 with EXO70 proteins.plantcell;31/11/2664/FX1F1fx1.

AvrRpm1 Functions as an ADP-Ribosyl Transferase to Modify NOI-domain Containing Proteins, Including Arabidopsis and Soybean RPM1-interacting Protein 4

The Pseudomonas syringae effector protein AvrRpm1 activates the Arabidopsis intracellular innate immune receptor protein RPM1 via modification of a second Arabidopsis protein, RIN4. Prior work has shown that AvrRpm1 induces phosphorylation of AtRIN4, but homology modeling indicated that AvrRpm1 may be an ADP-ribosyl transferase. Here we show that AvrRpm1 induces ADP-ribosylation of RIN4 proteins from both Arabidopsis and soybean within two highly conserved nitrate-induced (NOI) domains. It also ADP-ribosylates at least ten additional Arabidopsis NOI domain-containing proteins. The ADP-ribosylation activity of AvrRpm1 is required for subsequent phosphorylation on threonine 166 of Arabidopsis RIN4, an event that is necessary and sufficient for RPM1 activation. We also show that the C-terminal NOI domain of AtRIN4 interacts with the exocyst subunits EXO70B1, EXO70E1, EXO70E2 and EXO70F1. Mutation of either EXO70B1 or EXO70E2 inhibited secretion of callose induced by the bacterial flagellin-derived peptide flg22. Substitution of RIN4 threonine 166 with aspartate enhanced the association of AtRIN4 with EXO70E2, which we posit inhibits its callose deposition function. Collectively, these data indicate that AvrRpm1 ADP-ribosyl transferase activity contributes to virulence by promoting phosphorylation of RIN4 threonine 166, which inhibits the secretion of defense compounds by promoting the inhibitory association of RIN4 with EXO70 proteins.

Role of RIN4 in Regulating PAMP-Triggered Immunity and Effector-Triggered Immunity: Current Status and Future Perspectives

As sessile organisms, plants have developed sophisticated system to defend themselves against microbial attack. Since plants do not have specialized immune cells, all plant cells appear to have the innate ability to recognize pathogens and turn on an appropriate defense response. The plant innate immune system has two major branches: PAMPs (pathogen associated molecular patterns)-triggered immunity (PTI) and effector-triggered immunity (ETI). The ability to discriminate between self and non-self is a fundamental feature of living organisms, and it is a prerequisite for the activation of plant defenses specific to microbial infection. Arabidopsis cells express receptors that detect extracellular molecules or structures of the microbes, which are called collectively PAMPs and activate PTI. However, nucleotidebinding site leucine-rich repeats (NB-LRR) proteins mediated ETI is induced by direct or indirect recognition of effector molecules encoded by avr genes. In Arabidopsis, plasmamembrane localized multifunctional protein RIN4 (RPM1interacting protein 4) plays important role in both PTI and ETI. Previous studies have suggested that RIN4 functions as a negative regulator of PTI. In addition, many different bacterial effector proteins modify RIN4 to destabilize plant immunity and several NB-LRR proteins, including RPM1 (resistance to Pseudomonas syringae pv. maculicola 1), RPS2 (resistance to P. syringae 2) guard RIN4. This review summarizes the current studies that have described signaling mechanism of RIN4 function, modification of RIN4 by bacterial effectors and different interacting partner of RIN4 in defense related pathway. In addition, the emerging role of the RIN4 in plant physiology and intercellular signaling as it presents in exosomes will be discussed.

Regulated Disorder: Posttranslational Modifications Control the RIN4 Plant Immune Signaling Hub

RIN4 is an intensively studied immune regulator in Arabidopsis and is involved in perception of microbial features outside and bacterial effectors inside plant cells. Furthermore, RIN4 is conserved in land plants and is targeted for posttranslational modifications by several virulence proteins from the bacterial pathogen Pseudomonas syringae. Despite the important roles of RIN4 in plant immune responses, its molecular function is not known. RIN4 is an intrinsically disordered protein (IDP), except at regions where pathogen-induced posttranslational modifications take place. IDP act as hubs for protein complex formation due to their ability to bind to multiple client proteins and, thus, are important players in signal transduction pathways. RIN4 is known to associate with multiple proteins involved in immunity, likely acting as an immune-signaling hub for the formation of distinct protein complexes. Genetically, RIN4 is a negative regulator of immunity, but diverse posttranslational modifications can either enhance its negative regulatory function or, on the contrary, render it a potent immune activator. In this review, we describe the structural domains of RIN4 proteins, their intrinsically disordered regions, posttranslational modifications, and highlight the implications that these features have on RIN4 function. In addition, we will discuss the potential role of plasma membrane subdomains in mediating RIN4 protein complex formations.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

A Tomato Nucleotide Binding Sites-Leucine-Rich Repeat Gene Is Positively Involved in Plant Resistance to Phytophthora infestans

The nucleotide binding sites-leucine-rich repeat (NBS-LRR) genes are key regulatory components of plant to pathogens. Phytophthora infestans-inducible coding sequence encoding an NBS-LRR (SpNBS-LRR) protein in tomato (Solanum pimpinellifolium L3708) was cloned and characterized based on our RNA-Seq data and tomato genome. After sequence analysis, SpNBS-LRR was identified as a hydrophilic protein with no transmembrane topological structure and no signal peptide. SpNBS-LRR had a close genetic relationship to RPS2 of Arabidopsis thaliana by phylogenetic analysis. In addition, SpNBS-LRR gene was mainly expressed in root, with low expression observed in leaf and stem. To further investigate the role of SpNBS-LRR in tomato-P. infestans interaction, SpNBS-LRR was introduced in susceptible tomatoes and three transgenic lines with higher expression level of SpNBS-LRR were selected. These transgenic tomato plants that overexpressed SpNBS-LRR displayed greater resistance than wild-type tomato plants after infection with P. infestans, as shown by decreased disease index, lesion diameters, number of necrotic cells, P. infestans abundance, and higher expression levels of the defense-related genes. This information provides insight into SpNBS-LRR involved in the resistance of tomato to P. infestans infection and candidate for breeding to enhance biotic stress-resistance in tomato.

The role of type III effectors from Xanthomonas axonopodis pv. manihotis in virulence and suppression of plant immunity

Xanthomonas axonopodis pv. manihotis (Xam) causes cassava bacterial blight, the most important bacterial disease of cassava. Xam, like other Xanthomonas species, requires type III effectors (T3Es) for maximal virulence. Xam strain CIO151 possesses 17 predicted T3Es belonging to the Xanthomonas outer protein (Xop) class. This work aimed to characterize nine Xop effectors present in Xam CIO151 for their role in virulence and modulation of plant immunity. Our findings demonstrate the importance of XopZ, XopX, XopAO1 and AvrBs2 for full virulence, as well as a redundant function in virulence between XopN and XopQ in susceptible cassava plants. We tested their role in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) using heterologous systems. AvrBs2, XopR and XopAO1 are capable of suppressing PTI. ETI suppression activity was only detected for XopE4 and XopAO1. These results demonstrate the overall importance and diversity in functions of major virulence effectors AvrBs2 and XopAO1 in Xam during cassava infection.

Behind the lines-actions of bacterial type III effector proteins in plant cells

Pathogenicity of most Gram-negative plant-pathogenic bacteria depends on the type III secretion (T3S) system, which translocates bacterial effector proteins into plant cells. Type III effectors modulate plant cellular pathways to the benefit of the pathogen and promote bacterial multiplication. One major virulence function of type III effectors is the suppression of plant innate immunity, which is triggered upon recognition of pathogen-derived molecular patterns by plant receptor proteins. Type III effectors also interfere with additional plant cellular processes including proteasome-dependent protein degradation, phytohormone signaling, the formation of the cytoskeleton, vesicle transport and gene expression. This review summarizes our current knowledge on the molecular functions of type III effector proteins with known plant target molecules. Furthermore, plant defense strategies for the detection of effector protein activities or effector-triggered alterations in plant targets are discussed.

The HopF family of Pseudomonas syringae type III secreted effectors

Pseudomonas syringae is a bacterial phytopathogen that utilizes the type III secretion system to inject effector proteins into plant host cells. Pseudomonas syringae can infect a wide range of plant hosts, including agronomically important crops such as tomatoes and beans. The ability of P. syringae to infect such numerous hosts is caused, in part, by the diversity of effectors employed by this phytopathogen. Over 60 different effector families exist in P. syringae; one such family is HopF, which contains over 100 distinct alleles. Despite this diversity, research has focused on only two members of this family: HopF1 from P. syringae pathovar phaseolicola 1449B and HopF2 from P. syringae pathovar tomato DC3000. In this study, we review the research on HopF family members, including their host targets and molecular mechanisms of immunity suppression, and their enzymatic function. We also provide a phylogenetic analysis of this expanding effector family which provides a basis for a proposed nomenclature to guide future research. The extensive genetic diversity that exists within the HopF family presents a great opportunity to study how functional diversification on an effector family contributes to host specialization.

Transcriptomic Response to Nitric Oxide Treatment in Larix olgensis Henry

Larix olgensis Henry is an important coniferous species found in plantation forests in northeastern China, but it is vulnerable to pathogens. Nitric oxide (NO) is an important molecule involved in plant resistance to pathogens. To study the regulatory role of NO at the transcriptional level, we characterized the transcriptomic response of L. olgensis seedlings to sodium nitroprusside (SNP, NO donor) using Illumina sequencing and de novo transcriptome assembly. A significant number of putative metabolic pathways and functions associated with the unique sequences were identified. Genes related to plant pathogen infection (FLS2, WRKY33, MAPKKK, and PR1) were upregulated with SNP treatment. This report describes the potential contribution of NO to disease resistance in L. olgensis as induced by biotic stress. Our results provide a substantial contribution to the genomic and transcriptomic resources for L. olgensis, as well as expanding our understanding of the involvement of NO in defense responses at the transcriptional level.

Understanding the mechanism of atovaquone drug resistance in Plasmodium falciparum cytochrome b mutation Y268S using computational methods

The rapid appearance of resistant malarial parasites after introduction of atovaquone (ATQ) drug has prompted the search for new drugs as even single point mutations in the active site of Cytochrome b protein can rapidly render ATQ ineffective. The presence of Y268 mutations in the Cytochrome b (Cyt b) protein is previously suggested to be responsible for the ATQ resistance in Plasmodium falciparum (P. falciparum). In this study, we examined the resistance mechanism against ATQ in P. falciparum through computational methods. Here, we reported a reliable protein model of Cyt bc1 complex containing Cyt b and the Iron-Sulphur Protein (ISP) of P. falciparum using composite modeling method by combining threading, ab initio modeling and atomic-level structure refinement approaches. The molecular dynamics simulations suggest that Y268S mutation causes ATQ resistance by reducing hydrophobic interactions between Cyt bc1 protein complex and ATQ. Moreover, the important histidine contact of ATQ with the ISP chain is also lost due to Y268S mutation. We noticed the induced mutation alters the arrangement of active site residues in a fashion that enforces ATQ to find its new stable binding site far away from the wild-type binding pocket. The MM-PBSA calculations also shows that the binding affinity of ATQ with Cyt bc1 complex is enough to hold it at this new site that ultimately leads to the ATQ resistance.