The ELICITIN RESPONSE protein (ELR) from Solanum microdontum can recognize INF1 elicitin of Phytophthora infestans and trigger defense responses. ELR is a receptor-like protein (RLP) that lacks a ...cytoplasmic signaling domain and is anticipated to require interaction with a signaling-competent receptor-like kinase. SUPPRESSOR OF BIR1-1 (SOBIR1) has been proposed as a general interactor for RLPs involved in immunity and, as such, is a potential interactor for ELR. Here, we investigate whether SOBIR1 is required for response to INF1 and resistance to P. infestans and whether it associates with ELR. Our results show that virus-induced gene silencing of SOBIR1 in Nicotiana benthamiana leads to loss of INF1-triggered cell death and increased susceptibility to P. infestans. Using genetic complementation, we found that the kinase activity of SOBIR1 is required for INF1-triggered cell death. Coimmunoprecipitation experiments showed that ELR constitutively associates with potato SOBIR1 in planta, forming a bipartite receptor complex. Upon INF1 elicitation, this ELR-SOBIR1 complex recruits SERK3 (SOMATIC EMBRYOGENESIS RECEPTOR KINASE 3) leading to downstream signaling activation. Overall, our study shows that SOBIR1 is required for basal resistance to P. infestans and for INF1-triggered cell death and functions as an adaptor kinase for ELR.
Summary
Phytophthora infestans causes severe losses in potato production. The MAPK kinase StMKK1 was previously found to negatively regulate potato immunity to P. infestans. Our results showed that ...StMKK1 interacts with a protein tyrosine phosphatase, referred to as StPTP1a, and StMKK1 directly phosphorylates StPTP1a at residues Ser‐99, Tyr‐223 and Thr‐290. StPTP1a is a functional phosphatase and the phosphorylation of StPTP1a at these three residues enhances its stability and catalytic activity. StPTP1a negatively regulates potato immunity and represses SA‐related gene expression. Furthermore, StPTP1a interacts with, and dephosphorylates, the StMKK1 downstream signalling targets StMPK4 and −7 at their Tyr‐203 residue resulting in the repression of salicylic acid (SA)‐related immunity. Silencing of NbPTP1a + NbMPK4 or NbPTP1a + NbMPK7 abolished the plant immunity to P. infestans caused by NbPTP1a silencing, indicating that PTP1a functions upstream of NbMPK4 and NbMPK7. StMKK1 requires StPTP1a to negatively regulate SA‐related immunity and StPTP1a is phosphorylated and stabilized during immune activation to promote the de‐phosphorylation of StMPK4 and −7. Our results reveal that potato StMKK1 activates and stabilizes the tyrosine phosphatase StPTP1a that in its turn de‐phosphorylates StMPK4 and −7, thereby repressing plant SA‐related immunity.
Hydrolases such as subtilases, vacuolar processing enzymes (VPEs) and the proteasome play important roles during plant programmed cell death (PCD). We investigated hydrolase activities during PCD ...using activity‐based protein profiling (ABPP), which displays the active proteome using probes that react covalently with the active site of proteins. We employed tomato (Solanum lycopersicum) seedlings undergoing synchronized hypersensitive cell death by co‐expressing the avirulence protein Avr4 from Cladosporium fulvum and the tomato resistance protein Cf‐4. Cell death is blocked in seedlings grown at high temperature and humidity, and is synchronously induced by decreasing temperature and humidity. ABPP revealed that VPEs and the proteasome are not differentially active, but that activities of papain‐like cysteine proteases and serine hydrolases, including Hsr203 and P69B, increase before hypersensitive tissue collapse, whereas the activity of a carboxypeptidase‐like enzyme is reduced. Similar dynamics were observed for these enzymes in the apoplast of tomato challenged with C. fulvum. Unexpectedly, these challenged plants also displayed novel isoforms of secreted putative VPEs. In the absence of tissue collapse at high humidity, the hydrolase activity profile is already altered completely, demonstrating that changes in hydrolase activities precede hypersensitive tissue collapse.
Models are extensively used to describe the coevolution of plants and microbial attackers. Such models distinguish between different classes of plant immune responses, based on the type of danger ...signal that is recognized or on the strength of the defense response that the danger signal provokes. However, recent molecular and biochemical advances have shown that these dichotomies are blurred. With molecular proof in hand, we propose here to abandon the current classification of plant immune responses, and to define the different forms of plant immunity solely based on the site of microbe recognition – either extracellular or intracellular. Using this spatial partition, our ‘spatial immunity model’ facilitates a broadly inclusive, but clearly distinguishing nomenclature to describe immune signaling in plant–microbe interactions.
Any distinction between the types of immune responses triggered in plants should be solely based on the location where the immunogenic pattern is perceived.The dichotomy between patterns and effectors is blurred, which makes a classification of plant defense responses based on this dichotomy inappropriate.All leucine-rich repeat (LRR)-type cell-surface receptors (both receptor-like proteins, RLPs; and receptor-like kinases, RLKs) studied, recruit the regulatory LRR-RLK BAK1 upon their activation by extracellular immunogenic patterns (ExIPs).All LRR-RLPs studied appear to constitutively interact with SOBIR1 and recruit BAK1 upon ExIP perception, thereby providing a set of identical cytoplasmic kinase domains for downstream signaling.LRR-RLPs trigger a plethora of defense responses, with intensities ranging from moderate immunity to a strong hypersensitive response.
Resistance in tomato against race 1 strains of the fungal vascular wilt pathogens Verticillium dahliae and V. albo-atrum is mediated by the Ve locus. This locus comprises two closely linked inversely ...oriented genes, Ve1 and Ve2, which encode cell surface receptors of the extracellular leucine-rich repeat receptor-like protein (eLRR-RLP) type. While Ve1 mediates Verticillium resistance through monitoring the presence of the recently identified V. dahliae Ave1 effector, no functionality for Ve2 has been demonstrated in tomato. Ve1 and Ve2 contain 37 eLRRs and share 84% amino acid identity, facilitating investigation of Ve protein functionality through domain swapping. In this study it is shown that Ve chimeras in which the first thirty eLRRs of Ve1 were replaced by those of Ve2 remain able to induce HR and activate Verticillium resistance, and that deletion of these thirty eLRRs from Ve1 resulted in loss of functionality. Also the region between eLRR30 and eLRR35 is required for Ve1-mediated resistance, and cannot be replaced by the region between eLRR30 and eLRR35 of Ve2. We furthermore show that the cytoplasmic tail of Ve1 is required for functionality, as truncation of this tail results in loss of functionality. Moreover, the C-terminus of Ve2 fails to activate immune signaling as chimeras containing the C-terminus of Ve2 do not provide Verticillium resistance. Furthermore, Ve1 was found to interact through its C-terminus with the eLRR-containing receptor-like kinase (eLRR-RLK) interactor SOBIR1 that was recently identified as an interactor of eLRR-RLP (immune) receptors. Intriguingly, also Ve2 was found to interact with SOBIR1.
Mitogen‐activated protein kinase (MAPK) cascades play pivotal roles in plant responses to both biotic and abiotic stress. A screen of a Nicotiana benthamiana cDNA virus‐induced gene silencing (VIGS) ...library for altered plant responses to inoculation with Phytophthora infestans previously identified an NbMKK gene, encoding a clade D MAPKK that we renamed as NbMKK5, which is involved in immunity to P. infestans. To study the role of the potato orthologous gene, referred to as StMKK5, in the response to P. infestans, we transiently overexpressed StMKK5 in N. benthamiana and observed that cell death occurred at 2 days postinfiltration. Silencing of the highly conserved eukaryotic protein SGT1 delayed the StMKK5‐induced cell death, whereas silencing of the MAPK‐encoding gene NbSIPK completely abolished the cell death response. Further investigations showed that StMKK5 interacts with, and directly phosphorylates, StSIPK. Furthermore, both StMKK5 and StSIPK trigger salicylic acid (SA)‐ and ethylene (Eth)‐related gene expression, and co‐expression of the salicylate hydroxylase NahG with the negative regulator of Eth signalling CTR1 hampers StSIPK‐triggered cell death. This observation indicates that the cell death triggered by StMKK5‐StSIPK is dependent on the combination of SA‐ and Eth‐signalling. By introducing point mutations, we showed that the kinase activity of both StMKK5 and StSIPK is required for triggering cell death. Genetic analysis showed that StMKK5 depends on StSIPK to trigger plant resistance. Thus, our results define a potato StMKK5‐SIPK module that positively regulates immunity to P. infestans via activation of both the SA and Eth signalling pathways.
This study identified a potato StMKK5‐SIPK module that positively regulates immunity to Phytophthora infestans via activation of both the salicylic acid and ethylene signalling pathways.
Of PAMPs and Effectors: The Blurred PTI-ETI Dichotomy Thomma, Bart P.H.J; Nürnberger, Thorsten; Joosten, Matthieu H.A.J
The Plant cell,
2011, 20110101, 2011-Jan, 2011-01-00, Letnik:
23, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Typically, pathogen-associated molecular patterns (PAMPs) are considered to be conserved throughout classes of microbes and to contribute to general microbial fitness, whereas effectors are species, ...race, or strain specific and contribute to pathogen virulence. Both types of molecule can trigger plant immunity, designated PAMP-triggered and effector-triggered immunity (PTI and ETI, respectively). However, not all microbial defense activators conform to the common distinction between PAMPs and effectors. For example, some effectors display wide distribution, while some PAMPs are rather narrowly conserved or contribute to pathogen virulence. As effectors may elicit defense responses and PAMPs may be required for virulence, single components cannot exclusively be referred to by one of the two terms. Therefore, we put forward that the distinction between PAMPs and effectors, between PAMP receptors and resistance proteins, and, therefore, also between PTI and ETI, cannot strictly be maintained. Rather, as illustrated by examples provided here, there is a continuum between PTI and ETI. We argue that plant resistance is determined by immune receptors that recognize appropriate ligands to activate defense, the amplitude of which is likely determined by the level required for effective immunity.
Land cover changes following rewetting of 73 thousand hectares of peatland after the severe 2010 peat fires in Moscow Region (Russia) were monitored using multispectral remote sensing. The results ...revealed a reduction in the area of bare peat and dry grasslands, the rapid expansion of willow and birch vegetation, and a steady increase in wet grasslands and open water. Both the number and area of peat fires were clearly reduced compared to all wildfires in the region.
Monitoring large areas over longer periods generally implies using different satellites and sensors. The developed methodology enabled assessing the effectiveness of rewetting to reduce fire hazard as well as identifying areas that remain fire-prone and require additional restoration effort. The methodology proved to be robust for the long-term monitoring of the effect of rewetting large areas of peatlands, as required under the Paris Agreement.
Studies on plant–pathogen interactions often involve monitoring disease symptoms or responses of the host plant to pathogen‐derived immunogenic patterns, either visually or by staining the plant ...tissue. Both these methods have limitations with respect to resolution, reproducibility, and the ability to quantify the results. In this study we show that red light detection by the red fluorescent protein (RFP) channel of a multipurpose fluorescence imaging system that is probably available in many laboratories can be used to visualize plant tissue undergoing cell death. Red light emission is the result of chlorophyll fluorescence on thylakoid membrane disassembly during the development of a programmed cell death process. The activation of programmed cell death can occur during either a hypersensitive response to a biotrophic pathogen or an apoptotic cell death triggered by a necrotrophic pathogen. Quantifying the intensity of the red light signal enables the magnitude of programmed cell death to be evaluated and provides a readout of the plant immune response in a faster, safer, and nondestructive manner when compared to previously developed chemical staining methodologies. This application can be implemented to screen for differences in symptom severity in plant–pathogen interactions, and to visualize and quantify in a more sensitive and objective manner the intensity of the plant response on perception of a given immunological pattern. We illustrate the utility and versatility of the method using diverse immunogenic patterns and pathogens.
Plants undergoing cell death during pathogen infection or in response to an immunogenic pattern emit red light that can be detected and quantified with an imaging system available in many laboratories.
The tripartite genome of the negative-stranded RNA virus
(TSWV) is assembled, together with two viral proteins, the nucleocapsid protein and the RNA-dependent RNA polymerase, into infectious ...ribonucleoprotein complexes (RNPs). These two viral proteins are, together, essential for viral replication and transcription, yet our knowledge on the host factors supporting these two processes remains limited. To fill this knowledge gap, the protein composition of viral RNPs collected from TSWV-infected
plants, and of those collected from a reconstituted TSWV replicon system in the yeast
, was analysed. RNPs obtained from infected plant material were enriched for plant proteins implicated in (
) sugar and phosphate transport and (
) responses to cellular stress. In contrast, the yeast-derived viral RNPs primarily contained proteins implicated in RNA processing and ribosome biogenesis. The latter suggests that, in yeast, the translational machinery is recruited to these viral RNPs. To examine whether one of these cellular proteins is important for a TSWV infection, the corresponding
genes were targeted for virus-induced gene silencing, and these plants were subsequently challenged with TSWV. This approach revealed four host factors that are important for systemic spread of TSWV and disease symptom development.
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