The battle for chitin recognition in plant-microbe interactions

Fungal cell walls play dynamic functions in interaction of fungi with their surroundings. In pathogenic fungi, the cell wall is the first structure to make physical contact with host cells. An important structural component of fungal cell walls is chitin, a well-known elicitor of immune responses in plants. Research into chitin perception has sparked since the chitin receptor from rice was cloned nearly a decade ago. Considering the widespread nature of chitin perception in plants, pathogens evidently evolved strategies to overcome detection, including alterations in the composition of cell walls, modification of their carbohydrate chains and secretion of effectors to provide cell wall protection or target host immune responses. Also non-pathogenic fungi contain chitin in their cell walls and are recipients of immune responses. Intriguingly, various mutualists employ chitin-derived signaling molecules to prepare their hosts for the mutualistic relationship. Research on the various types of interactions has revealed different molecular components that play crucial roles and, moreover, that various chitin-binding proteins contain dissimilar chitin-binding domains across species that differ in affinity and specificity. Considering the various strategies from microbes and hosts focused on chitin recognition, it is evident that this carbohydrate plays a central role in plant-fungus interaction

Synthesis of HA/beta-TCP bioceramic foams from natural products

A novel technology for the preparation of bioceramic foams (BF) using a simple and economic procedure is presented. This technology combines two conventional methods to produce a tridimensional macroporous structure by using a sol-gel route, submitted afterward to a microwave treatment and thermal annealing. The use of agri-waste products on this procedure, such as egg shell and white egg recycle, represents an interesting way for waste management while developing potential commercial biomaterials. The use of egg shell as eco-compatible reactant instead of commercial ones and the egg white as foaming agent to produce a tridimensional macroporous structures has been optimized by using a sol-gel route. The crystalline phase and quantitative phase composition has been studied by Rietveld refinement and the optimization of the foaming process and determination of interconnected porosity by scanning electron microscopy, Hg porosimetry and X-ray micro-CT imaging. Our results show that BF samples showed a composition of 60 wt% HA (hydroxyapatite) and 40 wt% beta-TCP (beta-tricalcium phosphate) with a total porosity of approx. 70 % and a porosity ranging from 5 to 300 mu m. These features indicate that BF samples are ideal for bone regeneration, and they are produced in an easy and environmental friendly viable process

Soil composition and plant genotype determine benzoxazinoid-mediated plant–soil feedbacks in cereals

Plant–soil feedbacks refer to effects on plants that are mediated by soil modifications caused by the previous plant generation. Maize conditions the surrounding soil by secretion of root exudates including benzoxazinoids (BXs), a class of bioactive secondary metabolites. Previous work found that a BX-conditioned soil microbiota enhances insect resistance while reducing biomass in the next generation of maize plants. Whether these BX-mediated and microbially driven feedbacks are conserved across different soils and response species is unknown. We found the BX-feedbacks on maize growth and insect resistance conserved between two arable soils, but absent in a more fertile grassland soil, suggesting a soil-type dependence of BX feedbacks. We demonstrated that wheat also responded to BX-feedbacks. While the negative growth response to BX-conditioning was conserved in both cereals, insect resistance showed opposite patterns, with an increase in maize and a decrease in wheat. Wheat pathogen resistance was not affected. Finally and consistent with maize, we found the BX-feedbacks to be cultivar-specific. Taken together, BX-feedbacks affected cereal growth and resistance in a soil and genotype-dependent manner. Cultivar-specificity of BX-feedbacks is a key finding, as it hides the potential to optimize crops that avoid negative plant–soil feedbacks in rotations

Mixed infections alter transmission potential in a fungal plant pathogen

Infections by more than one strain of a pathogen predominate under natural conditions. Mixed infections can have significant, though often unpredictable, consequences for overall virulence, pathogen transmission and evolution. However, effects of mixed infection on disease development in plants often remain unclear and the critical factors that determine the outcome of mixed infections remain unknown. The fungus Zymoseptoria tritici forms genetically diverse infections in wheat fields. Here, for a range of pathogen traits, we experimentally decompose the infection process to determine how the outcomes and consequences of mixed infections are mechanistically realized. Different strains of Z. tritici grow in close proximity and compete in the wheat apoplast, resulting in reductions in growth of individual strains and in pathogen reproduction. We observed different outcomes of competition at different stages of the infection. Overall, more virulent strains had higher competitive ability during host colonization, and less virulent strains had higher transmission potential. We showed that within‐host competition can have a major effect on infection dynamics and pathogen population structure in a pathogen and host genotype‐specific manner. Consequently, mixed infections likely have a major effect on the development of septoria tritici blotch epidemics and the evolution of virulence in Z. tritici

Alteration of cell wall xylan acetylation triggers defense responses that counterbalance the immune deficiencies of plants impaired in the β‐subunit of the heterotrimeric G‐protein

[EN] Arabidopsis heterotrimeric G-protein complex modulates pathogen-associated molecular pattern-triggeredimmunity (PTI) and disease resistance responses to different types of pathogens. It also plays a role in plantcell wall integrity as mutants impaired in the Gb-(agb1-2)orGc-subunits have an altered wall compositioncompared with wild-type plants. Here we performed a mutant screen to identify suppressors ofagb1-2(sgb) that restore susceptibility to pathogens to wild-type levels. Out of the foursgbmutants (sgb10–sgb13)identified,sgb11is a new mutant allele ofESKIMO1(ESK1), which encodes a plant-specific polysaccharideO-acetyltransferase involved in xylan acetylation. Null alleles (sgb11/esk1-7)ofESK1restore to wild-typelevels the enhanced susceptibility ofagb1-2to the necrotrophic fungusPlectosphaerella cucumerina BMM(PcBMM), but not to the bacteriumPseudomonas syringaepv.tomatoDC3000 or to the oomyceteHyaloper-onospora arabidopsidis. The enhanced resistance toPcBMMof theagb1-2 esk1-7double mutant was notthe result of the re-activation of deficient PTI responses inagb1-2. Alteration of cell wall xylan acetylationcaused byESK1impairment was accompanied by an enhanced accumulation of abscisic acid, the constitu-tive expression of genes encoding antibiotic peptides and enzymes involved in the biosynthesis of trypto-phan-derived metabolites, and the accumulation of disease resistance-related secondary metabolites anddifferent osmolites. Theseesk1-mediated responses counterbalance the defective PTI andPcBMMsuscepti-bility ofagb1-2plants, and explain the enhanced drought resistance ofesk1plants. These results suggestthat a deficient PTI-mediated resistance is partially compensated by the activation of specific cell-wall-trig-gered immune responses.SISpanish Ministry of Economy and Competitiveness (MINECO) grants BIO2012-32910 to A.M.The Australian Research Council Centre of Excellence in Plant Cell Walls and matching funding from KTH (grants to V.B) and NIGMS (R01GM065989) and NSF (MCB-1713880) to A.M.J. The Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the US Department of Energy through the grant DE-FG02-05er15671 to A.M.J. funded technical support in this study. H.M. was supported by an IEF grant (SignWALLINg-624721) from the European Union, E.M. by a Juan de la Cierva Postdoctoral Fellow from MINECO, S.S. by the BRAVE Erasmus Mundi Program (European Union), and A.M.-B. was the recipient of a PIF fellow from Universidad Politécnica de Madrid

Arabidopsiscell wall composition determines disease resistance specificity and fitness

[EN] Plant cell walls are complex structures subject to dynamic remodeling in response to developmental and environmental cues and play essential functions in disease resistance responses. We tested the specific contribution of plant cell walls to immunity by determining the susceptibility of a set of Arabidopsis cell wall mutants (cwm) to pathogens with different parasitic styles: a vascular bacterium, a necrotrophic fungus, and a biotrophic oomycete. Remarkably, most cwm mutants tested (29/34; 85.3%) showed alterations in their resistance responses to at least one of these pathogens in comparison to wild-type plants, illustrating the relevance of wall composition in determining disease-resistance phenotypes. We found that the enhanced resistance of cwm plants to the necrotrophic and vascular pathogens negatively impacted cwm fitness traits, such as biomass and seed yield. Enhanced resistance of cwm plants is not only mediated by canonical immune pathways, like those modulated by phytohormones or microbeassociated molecular patterns, which are not deregulated in the cwm tested. Pectin-enriched wall fractions isolated from cwm plants triggered immune responses in wild-type plants, suggesting that wall-mediated defensive pathways might contribute to cwm resistance. Cell walls of cwm plants show a high diversity of composition alterations as revealed by glycome profiling that detect specific wall carbohydrate moieties. Mathematical analysis of glycome profiling data identified correlations between the amounts of specific wall carbohydrate moieties and disease resistance phenotypes of cwm plants. These data support the relevant and specific function of plant wall composition in plant immune response modulation and in balancing disease resistance/development trade-offs.SIThis work has been also financially supported by the Severo Ochoa Program for Centers of Excellence in R&D from the Agencia Estatal de Investigación of Spain (Grant SEV-2016-0672 (2017-2021) to the Centro de Biotecnología y Genómica de Plantas). In the frame of this program, H.M. was a postdoctoral fellow. H.M. was also supported by an Individual Fellowship grant (SignWALLINg-624721) from the European Union. E.M. was a Juan de la Cierva Postdoctoral Fellow from MINECO, and L.B. was a Formacion Personal Investigador fellow of MICIU. The generation of the CCRC-series of plant cell glycan-directed monoclonal antibodies used in this work was supported by the US NSF (DBI-0421683 and IOS 0923992) to M.G.H

Synthetic and structural studies on Pyrularia pubera thionin: a single-residue mutation enhances activity against Gram-negative bacteria

The thionin from Pyrularia pubera (Pp-TH), a 47-residue peptide with four internal disulfide bonds, was efficiently produced by chemical synthesis. Its antimicrobial activity in vitro against several representative pathogens (EC50=0.3–3.0 μM) was identical to that of natural Pp-TH. This peptide has a unique Asp32 instead of the consensus Arg found in other thionins of the same family. In order to evaluate the effect of this mutation, the Arg32 analogue (Pp-TH(D32R)) was also synthesized and showed a significant increase in antibiotic activity against several Gram-negative bacteria, whereas it retained the same activity against other pathogens. The overall structure of Pp-TH(D32R) was maintained, though a slight decrease in the helical content of the peptide was observed

Disruption of abscisic acid signaling constitutively activates Arabidopsis resistance to the necrotrophic fungus Plectosphaerella cucumerina.

Plant resistance to necrotrophic fungi is regulated by a complex set of signaling pathways that includes those mediated by the hormones salicylic acid (SA), ethylene (ET), jasmonic acid (JA), and abscisic acid (ABA). The role of ABA in plant resistance remains controversial, as positive and negative regulatory functions have been described depending on the plant-pathogen interaction analyzed. Here, we show that ABA signaling negatively regulates Arabidopsis (Arabidopsis thaliana) resistance to the necrotrophic fungus Plectosphaerella cucumerina. Arabidopsis plants impaired in ABA biosynthesis, such as the aba1-6 mutant, or in ABA signaling, like the quadruple pyr/pyl mutant (pyr1pyl1pyl2pyl4), were more resistant to P. cucumerina than wild-type plants. In contrast, the hab1-1abi1-2abi2-2 mutant impaired in three phosphatases that negatively regulate ABA signaling displayed an enhanced susceptibility phenotype to this fungus. Comparative transcriptomic analyses of aba1-6 and wild-type plants revealed that the ABA pathway negatively regulates defense genes, many of which are controlled by the SA, JA, or ET pathway. In line with these data, we found that aba1-6 resistance to P. cucumerina was partially compromised when the SA, JA, or ET pathway was disrupted in this mutant. Additionally, in the aba1-6 plants, some genes encoding cell wall-related proteins were misregulated. Fourier transform infrared spectroscopy and biochemical analyses of cell walls from aba1-6 and wild-type plants revealed significant differences in their Fourier transform infrared spectratypes and uronic acid and cellulose contents. All these data suggest that ABA signaling has a complex function in Arabidopsis basal resistance, negatively regulating SA/JA/ET-mediated resistance to necrotrophic fungi

YODA MAPK kinase kinase regulates a novel immunity pathway conferring broad-spectrum resistance to pathogens

Plant mitogen-activated protein kinase (MAPK) casca des transduce environmental molecular signals and developmental cues into cellular responses. Among these signals are the pathogen-associated molecular patterns (PAMPs) that upon recognition by plant pattern recognition receptors (PRR), including Receptor-Like Kinases (RLKs), activate MAPK cascades that regulate PAMP-triggered immunity responses (PTI)

Signwalling: signals derived from arabiopsis cell wall activate specific resistance to pathogens

The cell wall is a dynamic structure that regulates both constitutive and inducible plant defence responses. Different molecules o DAMPs (damage-associated molecular patterns) can be released from plant cell walls upon pathogen infection or wounding and can trigger immune responses. To further characterize the function of cell wall on the regulation of these immune responses, we have performed a biased resistance screening of putative/well-characterized primary/secondary Arabidopsis thaliana cell wall mutants (cwm). In this screening we have identified more than 20 cwm mutants with altered susceptibility/resistance to at least one of the following pathogens: the necrotrophic fungi Plectosphaerella cucumerina, the vascular bacterium Ralstonia solanacearum, the biotrophic oomycete Hyaloperonospora arabidopsidis and the powdery mildew fungus Erisyphe cruciferarum. We found that cell wall extracts from some of these cwm plants contain novel DAMPs that activate immune responses and conferred enhanced resistance to particular pathogens when they were applied to wild-type plants. Using glycomic profiling we have performed an initial characterization of the active carbohydrate structures present in these cwm wall fractions, and we have determined the signalling pathways regulated by thesse fractions. . The data generated with this collection of wall mutants support the existence of specific correlations between cell wall structure/composition, resistance to particular type of pathogens and plant fitness. Remarkably, we have identified specific cwm mutations that uncoupled resistance to pathogens from plant trade-offs, further indicating the plasticity of wall structures in the regulation of plant immune responses