Summary
Heterodimeric complexes incorporating the lipase‐like proteins EDS1 with PAD4 or SAG101 are central hubs in plant innate immunity. EDS1 functions encompass signal relay from TIR ...domain‐containing intracellular NLR‐type immune receptors (TNLs) towards RPW8‐type helper NLRs (RNLs) and, in Arabidopsis thaliana, bolstering of signaling and resistance mediated by cell‐surface pattern recognition receptors (PRRs). Increasing evidence points to the activation of EDS1 complexes by small molecule binding.
We used CRISPR/Cas‐generated mutant lines and agroinfiltration‐based complementation assays to interrogate functions of EDS1 complexes in Nicotiana benthamiana.
We did not detect impaired PRR signaling in N. benthamiana lines deficient in EDS1 complexes or RNLs. Intriguingly, in assays monitoring functions of SlEDS1‐NbEDS1 complexes in N. benthamiana, mutations within the SlEDS1 catalytic triad could abolish or enhance TNL immunity. Furthermore, nuclear EDS1 accumulation was sufficient for N. benthamiana TNL (Roq1) immunity.
Reinforcing PRR signaling in Arabidopsis might be a derived function of the TNL/EDS1 immune sector. Although Solanaceae EDS1 functionally depends on catalytic triad residues in some contexts, our data do not support binding of a TNL‐derived small molecule in the triad environment. Whether and how nuclear EDS1 activity connects to membrane pore‐forming RNLs remains unknown.
Summary
Leucine‐rich repeat‐receptor‐like proteins (LRR‐RLPs) and LRR‐receptor‐like kinases (LRR‐RLKs) trigger immune signalling to promote plant resistance against pathogens. LRR‐RLPs lack an ...intracellular kinase domain, and several of these receptors have been shown to constitutively interact with the LRR‐RLK Suppressor of BIR1‐1/EVERSHED (SOBIR1/EVR) to form signalling‐competent receptor complexes. Ligand perception by LRR‐RLPs initiates recruitment of the co‐receptor BRI1‐Associated Kinase 1/Somatic Embryogenesis Receptor Kinase 3 (BAK1/SERK3) to the LRR‐RLP/SOBIR1 complex, thereby activating LRR‐RLP‐mediated immunity. We employed phosphorylation analysis of in planta‐produced proteins, live cell imaging, gene silencing and co‐immunoprecipitation to investigate the roles of SOBIR1 and BAK1 in immune signalling. We show that Arabidopsis thaliana (At) SOBIR1, which constitutively activates immune responses when overexpressed in planta, is highly phosphorylated. Moreover, in addition to the kinase activity of SOBIR1 itself, kinase‐active BAK1 is essential for AtSOBIR1‐induced constitutive immunity and for the phosphorylation of AtSOBIR1. Furthermore, the defence response triggered by the tomato LRR‐RLP Cf‐4 on perception of Avr4 from the extracellular pathogenic fungus Cladosporium fulvum is dependent on kinase‐active BAK1. We argue that, in addition to the trans‐autophosphorylation of SOBIR1, it is likely that SOBIR1 and BAK1 transphosphorylate, and thereby activate the receptor complex. The signalling‐competent cell surface receptor complex subsequently activates downstream cytoplasmic signalling partners to initiate RLP‐mediated immunity.
Summary
Ubiquitin‐like domain‐containing proteins (UDPs) are involved in the ubiquitin‐proteasome system because of their ability to interact with the 26S proteasome. Here, we identified potato StUDP ...as a target of the Phytophthora infestans RXLR effector Pi06432 (PITG_06432), which supresses the salicylic acid (SA)‐related immune pathway.
By overexpressing and silencing of StUDP in potato, we show that StUDP negatively regulates plant immunity against P. infestans. StUDP interacts with, and destabilizes, the 26S proteasome subunit that is referred to as REGULATORY PARTICLE TRIPLE‐A ATP‐ASE (RPT) subunit StRPT3b. This destabilization represses the proteasome activity. Proteomic analysis and Western blotting show that StUDP decreases the stability of the master transcription factor SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) in SA biosynthesis.
StUDP negatively regulates the SA signalling pathway by repressing the proteasome activity and destabilizing StSARD1, leading to a decreased expression of the SARD1‐targeted gene ISOCHORISMATE SYNTHASE 1 and thereby a decrease in SA content. Pi06432 stabilizes StUDP, and it depends on StUDP to destabilize StRPT3b and thereby supress the proteasome activity.
Our study reveals that the P. infestans effector Pi06432 targets StUDP to hamper the homeostasis of the proteasome by the degradation of the proteasome subunit StRPT3b and thereby suppresses SA‐related immunity.
Sphagnum biomass is a promising material that could be used as a substitute for peat in growing media and can be sustainably produced by converting existing drainage‐based peatland agriculture into ...wet, climate‐friendly agriculture (paludiculture). Our study focuses on yield maximization of Sphagnum as a crop.
We tested the effects of three water level regimes and of phosphorus or potassium fertilization on the growth of four Sphagnum species (S. papillosum, S. palustre, S. fimbriatum, S. fallax). To simulate field conditions in Central and Western Europe we carried out a glasshouse experiment under nitrogen‐saturated conditions.
A constant high water table (remaining at 2 cm below capitulum during growth) led to highest productivity for all tested species. Water table fluctuations between 2 and 9 cm below capitulum during growth and a water level 2 cm below capitulum at the start but falling relatively during plant growth led to significantly lower productivity. Fertilization had no effect on Sphagnum growth under conditions with high atmospheric deposition such as in NW Germany (38 kg N, 0.3 kg P, 7.6 kg K·ha−1·year−1).
Large‐scale maximization of Sphagnum yields requires precise water management, with water tables just below the capitula and rising with Sphagnum growth. The nutrient load in large areas of Central and Western Europe from atmospheric deposition and irrigation water is high but, with an optimal water supply, does not hamper Sphagnum growth, at least not of regional provenances of Sphagnum.
Sphagnum grows best with water just below its head even under high nutrient loads.
Resistance against the leaf mold fungus Cladosporium fulvum is mediated by the tomato Cf proteins which belong to the class of receptor-like proteins and indirectly recognize extracellular avirulence ...proteins (Avrs) of the fungus. Apart from triggering disease resistance, Avrs are believed to play a role in pathogenicity or virulence of C. fulvum. Here, we report on the avirulence protein Avr4, which is a chitin-binding lectin containing an invertebrate chitin-binding domain (CBM14). This domain is found in many eukaryotes, but has not yet been described in fungal or plant genomes. We found that interaction of Avr4 with chitin is specific, because it does not interact with other cell wall polysaccharides. Avr4 binds to chitin oligomers with a minimal length of three N-acetyl glucosamine residues. In vitro, Avr4 protects chitin against hydrolysis by plant chitinases. Avr4 also binds to chitin in cell walls of the fungi Trichoderma viride and Fusarium solani f. sp. phaseoli and protects these fungi against normally deleterious concentrations of plant chitinases. In situ fluorescence studies showed that Avr4 also binds to cell walls of C. fulvum during infection of tomato, where it most likely protects the fungus against tomato chitinases, suggesting that Avr4 is a counter-defensive virulence factor.
Abstract
Peatlands have been drained for land use for a long time and on a large scale, turning them from carbon and nutrient sinks into respective sources, diminishing water regulation capacity, ...causing surface height loss and destroying biodiversity. Over the last decades, drained peatlands have been rewetted for biodiversity restoration and, as it strongly decreases greenhouse gas emissions, also for climate protection. We quantify restoration success by comparing 320 rewetted fen peatland sites to 243 near-natural peatland sites of similar origin across temperate Europe, all set into perspective by 10k additional European fen vegetation plots. Results imply that rewetting of drained fen peatlands induces the establishment of tall, graminoid wetland plants (helophytisation) and long-lasting differences to pre-drainage biodiversity (vegetation), ecosystem functioning (geochemistry, hydrology), and land cover characteristics (spectral temporal metrics). The Paris Agreement entails the rewetting of 500,000 km
2
of drained peatlands worldwide until 2050-2070. A better understanding of the resulting locally novel ecosystems is required to improve planning and implementation of peatland rewetting and subsequent management.
Enterobacter sakazakii is an opportunistic pathogen that can cause infections in neonates. This study further clarifies the taxonomy of isolates described as E. sakazakii and completes the formal ...description of the proposed reclassification of these organisms as novel species and subspecies within a proposed novel genus, Cronobacter gen. nov. E. sakazakii was first defined in 1980, however recent polyphasic taxonomic analysis has determined that this group of organisms consists of several genomospecies. In this study, the phenotypic descriptions of the proposed novel species are expanded using Biotype 100 and Biolog Phenotype MicroArray data. Further DNA-DNA hybridization experiments showed that malonate-positive strains within the E. sakazakii genomospecies represent a distinct species, not a subspecies. DNA-DNA hybridizations also determined that phenotypically different strains within the proposed species, Cronobacter dublinensis sp. nov., belong to the same species and can be considered as novel subspecies. Based on these analyses, the following alternative classifications are proposed: Cronobacter sakazakii gen. nov., comb. nov. type strain ATCC 29544(T) (=NCTC 11467(T)); Cronobacter malonaticus sp. nov. type strain CDC 1058-77(T) (=LMG 23826(T)=DSM 18702(T)); Cronobacter turicensis sp. nov. type strain z3032(T) (=LMG 23827(T)=DSM 18703(T)); Cronobacter muytjensii sp. nov. type strain ATCC 51329(T) (=CIP 103581(T)); Cronobacter dublinensis sp. nov. type strain DES187(T) (=LMG 23823(T)=DSM 18705(T)); Cronobacter dublinensis subsp. dublinensis subsp. nov. type strain DES187(T) (=LMG 23823(T)=DSM 18705(T)); Cronobacter dublinensis subsp. lausannensis subsp. nov. type strain E515(T) (=LMG 23824=DSM 18706(T)), and Cronobacter dublinensis subsp. lactaridi subsp. nov. type strain E464(T) (=LMG 23825(T)=DSM 18707(T)).
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
Potato is the third most important food crop worldwide. Potato production suffers from severe diseases caused by multiple detrimental plant pathogens, and broad‐spectrum disease resistance ...genes are rarely identified in potato. Here we identified the potato non‐specific lipid transfer protein StLTPa, which enhances species none‐specific disease resistance against various pathogens, such as the oomycete pathogen Phytophthora infestans, the fungal pathogens Botrytis cinerea and Verticillium dahliae, and the bacterial pathogens Pectobacterium carotovorum and Ralstonia solanacearum. The StLTPa overexpression potato lines do not show growth penalty. Furthermore, we provide evidence that StLTPa binds to lipids present in the plasma membrane (PM) of the hyphal cells of P. infestans, leading to an increased permeability of the PM. Adding of PI(3,5)P2 and PI(3)P could compete the binding of StLTPa to pathogen PM and reduce the inhibition effect of StLTPa. The lipid‐binding activity of StLTPa is essential for its role in pathogen inhibition and promotion of potato disease resistance. We propose that StLTPa enhances potato broad‐spectrum disease resistance by binding to, and thereby promoting the permeability of the PM of the cells of various pathogens. Overall, our discovery illustrates that increasing the expression of a single gene in potato enhances potato disease resistance against different pathogens without growth penalty.
Soybean is a major source of oil and proteins worldwide. The demand for soybean has increased in Africa, driven by the growing feed industry for poultry, aquaculture and home consumption in the form ...of processed milk, baked beans and for blending with maize and wheat flour. Soybean, in addition to being a major source of cooking oil, is also used in other industrial processes such as in the production of paints and candle wax. The demand for soybean in Africa so far outweighs the supply, hence the deficit is mainly covered through imports of soybean products such as soybean meal. The area under soybean production has increased in response to the growing demand, a trend that is expected to continue in the coming years. As the production area increases, diseases and insect pests, declining soil fertility and other abiotic factors pose a major challenge. Soybean rust disease, caused by the fungus Phakopsora pachyrhizi, presents one of the major threats to soybean production in Africa due to its rapid spread as a result of the ease by which its spores are dispersed by the wind. Disease control by introducing resistant soybean varieties has been difficult due to the presence of different populations of the fungus that vary in pathogenicity, virulence and genetic composition. Improved understanding of the dynamics of rust ecology, epidemiology and population genetics will enhance the effectiveness of targeted interventions that, in turn, will safeguard soybean productivity.
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