Biomedical subjects

Thomas Boller

Publications and source records attributed to Thomas Boller.

27 records · Page 2Linked to original sources

PubMed2003

A plasma membrane syntaxin is phosphorylated in response to the bacterial elicitor flagellin.

In vivo pulse labeling of suspension-cultured Arabidopsis cells with [32P]orthophosphate allows a systematic analysis of dynamic changes in protein phosphorylation. Here, we use this technique to investigate signal transduction events at the plant plasma membrane triggered upon perception of microbial elicitors of defense responses, using as a model elicitor flg22, a peptide corresponding to the most conserved domain of bacterial flagellin. We demonstrate that two-dimensional gel electrophoresis in conjunction with mass spectrometry is a suitable tool for the identification of intrinsic membrane proteins, and we show that among them a syntaxin, AtSyp122, is phosphorylated rapidly in response to flg22. Although incorporation of radioactive phosphate into the protein only occurs significantly after elicitation, immunoblot analysis after two-dimensional gel separation indicates that the protein is also phosphorylated prior to elicitation. These results indicate that flg22 elicits either an increase in the rate of turnover of phosphate or an additional de novo phosphorylation event. In vitro, phosphorylation of AtSyp122 is calcium-dependent. In vitro phosphorylated peptides separated by two-dimensional thin layer chromatography comigrate with two of the three in vivo phosphopeptides, indicating that this calcium-dependent phosphorylation is biologically relevant. These results indicate a regulatory link between elicitor-induced calcium fluxes and the rapid phosphorylation of a syntaxin. Because syntaxins are known to be important in membrane fusion and exocytosis, we hypothesize that one of the functions of the calcium signal is to stimulate exocytosis of defense-related proteins and compounds.

Amino Acid Sequence↗

PubMed2003

Impact of land use intensity on the species diversity of arbuscular mycorrhizal fungi in agroecosystems of Central Europe.

The impact of land use intensity on the diversity of arbuscular mycorrhizal fungi (AMF) was investigated at eight sites in the "three-country corner" of France, Germany, and Switzerland. Three sites were low-input, species-rich grasslands. Two sites represented low- to moderate-input farming with a 7-year crop rotation, and three sites represented high-input continuous maize monocropping. Representative soil samples were taken, and the AMF spores present were morphologically identified and counted. The same soil samples also served as inocula for "AMF trap cultures" with Plantago lanceolata, Trifolium pratense, and Lolium perenne. These trap cultures were established in pots in a greenhouse, and AMF root colonization and spore formation were monitored over 8 months. For the field samples, the numbers of AMF spores and species were highest in the grasslands, lower in the low- and moderate-input arable lands, and lowest in the lands with intensive continuous maize monocropping. Some AMF species occurred at all sites ("generalists"); most of them were prevalent in the intensively managed arable lands. Many other species, particularly those forming sporocarps, appeared to be specialists for grasslands. Only a few species were specialized on the arable lands with crop rotation, and only one species was restricted to the high-input maize sites. In the trap culture experiment, the rate of root colonization by AMF was highest with inocula from the permanent grasslands and lowest with those from the high-input monocropping sites. In contrast, AMF spore formation was slowest with the former inocula and fastest with the latter inocula. In conclusion, the increased land use intensity was correlated with a decrease in AMF species richness and with a preferential selection of species that colonized roots slowly but formed spores rapidly.

Agriculture↗

PubMed2002

Molecular sensing of bacteria in plants. The highly conserved RNA-binding motif RNP-1 of bacterial cold shock proteins is recognized as an elicitor signal in tobacco.

To detect microbial infection multicellular organisms have evolved sensing systems for pathogen-associated molecular patterns (PAMPs). Here, we identify bacterial cold shock protein (CSP) as a new such PAMP that acts as a highly active elicitor of defense responses in tobacco. Tobacco cells perceive a conserved domain of CSP and synthetic peptides representing 15 amino acids of this domain-induced responses at subnanomolar concentrations. Central to the elicitor-active domain is the RNP-1 motif KGFGFITP, a motif conserved also in many RNA- and DNA-binding proteins of eukaryotes. Csp15-Nsyl, a peptide representing the domain with highest homology to csp15 in a protein of Nicotiana sylvestris exhibited only weak activity in tobacco cells. Crystallographic and genetic data from the literature show that the RNP-1 domain of bacterial CSPs resides on a protruding loop and exposes a series of aromatic and basic side chains to the surface that are essential for the nucleotide-binding activity of CSPs. Similarly, these side chains were also essential for elicitor activity and replacement of single residues in csp15 with Ala strongly reduced or abolished activity. Most strikingly, csp15-Ala10, a peptide with the RNP-1 motif modified to KGAGFITP, lacked elicitor activity but acted as a competitive antagonist for CSP-related elicitors. Bacteria commonly have a small family of CSP-like proteins including both cold-inducible and noninducible members, and Csp-related elicitor activity was detected in extracts from all bacteria tested. Thus, the CSP domain containing the RNP-1 motif provides a structure characteristic for bacteria in general, and tobacco plants have evolved a highly sensitive chemoperception system to detect this bacterial PAMP.

Agrobacterium tumefaciens↗

PubMed2002

MAP kinase signalling cascade in Arabidopsis innate immunity.

There is remarkable conservation in the recognition of pathogen-associated molecular patterns (PAMPs) by innate immune responses of plants, insects and mammals. We developed an Arabidopsis thaliana leaf cell system based on the induction of early-defence gene transcription by flagellin, a highly conserved component of bacterial flagella that functions as a PAMP in plants and mammals. Here we identify a complete plant MAP kinase cascade (MEKK1, MKK4/MKK5 and MPK3/MPK6) and WRKY22/WRKY29 transcription factors that function downstream of the flagellin receptor FLS2, a leucine-rich-repeat (LRR) receptor kinase. Activation of this MAPK cascade confers resistance to both bacterial and fungal pathogens, suggesting that signalling events initiated by diverse pathogens converge into a conserved MAPK cascade.

Arabidopsis↗

PubMed2002

Mixed inoculation alters infection success of strains of the endophyte Epichloë bromicola on its grass host Bromus erectus.

Within-host competition in multiply infected hosts is considered an important component of host-parasite interactions, but experimental studies on the dynamics of multiple infections are still rare. We measured the infection frequencies of four strains of the fungal endophyte Epichloë bromicola on two genotypes of its host plant Bromus erectus after single- and double-strain inoculation. Double-strain inoculations resulted in fewer double, but more single, infections than expected on the basis of infection frequencies in single-strain inoculations. In most cases, only one of the two strains established an infection, and strains differed in their overall competitive ability. This pattern resembles the mutual exclusion scenarios in some theoretical models of parasite evolution. In addition, competitive ability varied with host genotype, which may represent a mechanism for the coexistence of strains in a population. Hence, considering the genetic variation in both host and parasite may be important for a better understanding of within-host dynamics and their role in epidemiology or (co)evolution.

Biological Evolution↗

PubMed2002

The growth defect of lrt1, a maize mutant lacking lateral roots, can be complemented by symbiotic fungi or high phosphate nutrition.

The growth of three maize (Zea mays L.) mutants, each impaired in the formation of one individual element of its root system, was compared under "natural" limiting phosphate conditions (0.1 mM). Mutant plants exhibiting a reduction in root hairs (rth3-1) or a depletion of crown and brace roots (rtcs) grew as well as the corresponding wild-type plants. However, mutant plants lacking lateral roots (lrt1) showed a strong reduction in plant growth. The growth defect of lrt1 was overcome when it was grown in association with an arbuscular mycorrhizal fungus, Glomus mosseae. Establishment of symbiosis was associated with the occurrence of a new type of lateral root. These new lateral roots were stunted and highly branched, giving rise to a bush-like structure. Supply of high phosphate (1 microM) ameliorated the growth of lrt1 plants too, but less efficiently than the symbiosis did. Hence, arbuscular mycorrhizal fungi as well as phosphate functionally complemented the lrt1 mutation.

Fungi↗

PubMed2002

Flagellin perception: a paradigm for innate immunity.

There are surprising similarities between how animals and plants perceive pathogens. In animals, innate immunity is based on the recognition of pathogen-associated molecular patterns. This is mediated by the Toll-like receptor (TLR) family, which rapidly induce the innate immunity response, a first line of defence against infectious disease. Plants have highly sensitive perception systems for general elicitors and they respond to these stimuli with a defence response. One of these general elicitors is flagellin, the main component of the bacterial flagellum. Genetic analysis in Arabidopsis has shown that FLS2, which encodes a receptor-like kinase, is essential for flagellin perception. FLS2 shares homology with the TLR family, and TLR5 is responsible for flagellin perception in mammals.

Animals↗

PubMed2002

Ectomycorrhiza: gene expression, metabolism and the wood-wide web.

In the ectomycorrhizal symbiosis between fungi and trees, the fungus completely ensheaths the tree roots and takes over water and mineral nutrient supply, while the plant supplies photosynthate. Recent work has focussed on gene expression in the two partners, on the effects of global change and nitrogen deposition rate on the symbiosis, and on the role of mycorrhizal fungi in connecting individual plants to form a 'wood-wide web'.

Ecosystem↗

PubMed2002

Induction of trehalase in Arabidopsis plants infected with the trehalose-producing pathogen Plasmodiophora brassicae.

Various microorganisms produce the disaccharide trehalose during their symbiotic and pathogenic interactions with plants. Trehalose has strong effects on plant metabolism and growth; therefore, we became interested to study its possible role in the interaction of Arabidopsis thaliana with Plasmodiophora brassicae, the causal agent of clubroot disease. We found that trehalose accumulated strongly in the infected organs (i.e., the roots and hypocotyls) and, to a lesser extent, in the leaves and stems of infected plants. This accumulation pattern of trehalose correlated with the expression of a putative trehalose-6-phosphate synthase (EC 2.4.1.15) gene from P. brassicae, PbTPS1. Clubroot formation also resulted in an induction of the Arabidopsis trehalase gene, ATTRE1, and in a concomitant increase in trehalase (EC 3.2.1.28) activity in the roots and hypocotyls, but not in the leaves and stems of infected plants. Thus, induction of ATTRE1 expression was probably responsible for the increased trehalase activity. Trehalase activity increased before trehalose accumulated; therefore, it is unlikely that trehalase was induced by its substrate. The induction of trehalase may be part of the plant's defense response and may prevent excess accumulation of trehalose in the plant cells, where it could interfere with the regulation of carbon metabolism.

Amino Acid Sequence↗