Biology subjects

Meinhardt, S.

Publications and source records attributed to Meinhardt, S..

3 recordsLinked to original sources

bioRxiv2023

A barley MLA receptor is targeted by a non-ribosomal peptide effector of the necrotrophic spot blotch fungus for disease susceptibility

The evolutionary history of plant interactions with necrotrophic pathogens that feed on dying host cells and their virulence mechanisms remains fragmentary. We have isolated the barley gene Scs6, which is required for the necrotrophic fungus Bipolaris sorokiniana isolate ND90Pr to cause spot blotch disease. Scs6 is located at the disease resistance gene locus Mildew locus a (Mla) and encodes an intracellular nucleotide-binding leucine-rich repeat receptor (NLR). In transgenic barley, Scs6 is sufficient to confer susceptibility to ND90Pr in accessions naturally lacking the receptor, resulting in infection-associated host cell death. Expression of Scs6 in evolutionarily distant Nicotiana benthamiana reconstitutes a cell death response to an uncharacterized non-ribosomal peptide effector produced by ND90Pr-specific non-ribosomal peptide synthetases (NRPSs) encoded at the VHv1 virulence locus. Our data suggest that the heat-resistant effector directly activates the SCS6 receptor. Scs6 is an allelic variant of functionally diversified Mla resistance genes each conferring strain-specific immunity to barley powdery mildew isolates with a matching proteinaceous pathogen effector. Domain swaps between MLA and SCS6 NLRs and expression of the resulting hybrid proteins in N. benthamiana reveal that the SCS6 leucine-rich repeat domain is a specificity determinant for the NRPS-derived effector to activate the receptor. Scs6 evolved after the divergence of barley from wheat and is maintained in several wild barley populations with an incidence of 8%, suggesting a beneficial function for the host. Evolution of the bona fide immune receptor SCS6 targeted by the NRPS-derived effector was key for the emergence of strain-specific spot blotch disease in domesticated barley.

plant biology↗

bioRxiv2023

Fructose-1-kinase has pleiotropic roles in Escherichia coli

In Escherichia coli, the master transcription regulator Catabolite Repressor Activator (Cra) regulates >100 genes in central metabolism. Cra binding to DNA is allosterically regulated by binding to fructose-1-phosphate (F-1-P), but the only documented source of F-1-P is from the concurrent import and phosphorylation of exogenous fructose. Thus, many have proposed that fructose-1,6-bisphosphate (F-1,6-BP) is also a physiological regulatory ligand. However, the role of F-1,6-BP has been widely debated. Here, we report that the E. coli enzyme fructose-1-kinase (FruK) can carry out its "reverse" reaction under physiological substrate concentrations to generate F-1-P from F-1,6-BP. We further show that FruK directly binds Cra with nanomolar affinity and forms higher order, heterocomplexes. Growth assays with a {Delta}fruK strain and fruK complementation show that FruK has a broader role in metabolism than fructose catabolism. The {Delta}fruK strain also alters biofilm formation. Since fruK itself is repressed by Cra, these newly-reported events add layers to the dynamic regulation of E. coli central metabolism that occur in response to changing nutrients. These findings might have wide-spread relevance to other {gamma}-proteobacteria, which conserve both Cra and FruK.

microbiology↗

bioRxiv2017

Protein-protein interactions with fructose-1-kinase alter function of the central Escherichia coli transcription regulator, Cra

In E. coli, the master transcription regulator Cra regulates >100 genes in central metabolism by binding upstream DNA operator sequences. Genes encoding glycolytic enzymes are repressed, whereas those for gluconeogenesis and the citric acid cycle are activated. Cra-DNA binding is allosterically diminished by binding to either fructose-1-phosphate (F-1-P, generated upon fructose import) or fructose-1,6-bisphosphate (F-1,6-BP). F-1,6-BP is generated from F-1-P by the enzyme fructose-1-kinase (FruK) or from other sugars and is a key intermediate in glycolysis. Here, we report that Cra directly interacts with FruK to form a tight protein-protein complex. Further, growth assays with a fruK knockout strain show that FruK has a broader role in metabolism than its known role in fructose catabolism. Biochemical experiments show that F-1,6-BP binding enhances either the Cra/FruK interaction and/or CRA binding to DNA and that FruK can catalyze the reverse reaction of F-1,6-BP to F-1-P. Results were used to propose a model in which the Cra-FruK complex enhances activation of gluconeogenic genes. Finally, since FruK itself is repressed by Cra, these newly-reported events add layers to the dynamic regulation of E. coli central metabolism that occur in response to changing nutrients.

microbiology↗