Biology subjects

Kümmel, F.

Publications and source records attributed to Kümmel, F..

4 recordsLinked to original sources

bioRxiv2025

Resources for molecular studies of unculturable obligate biotrophic fungal plant pathogens using their saprotrophic relatives

Obligate biotrophic plant pathogens like the powdery mildew fungi commit to a closely dependent relationship with their plant hosts and have lost the ability to grow and reproduce independently. Thus, at present, these organisms are not amenable to in vitro cultivation, which is a prerequisite for effective genetic modification and functional molecular studies. Saprotrophic fungi of the family Arachnopezizaceae are the closest known extant relatives of the powdery mildew fungi and may hold great potential for studying genetic components of their obligate biotrophic lifestyle. Here, we established telomere-to-telomere genome assemblies for two representatives of this family, Arachnopeziza aurata and A. aurelia. Both species harbor haploid genomes that are composed of 16 chromosomes at a genome size of 43.1 and 46.3 million base-pairs, respectively, which, in contrast to most powdery mildew genomes that are transposon-enriched, show a repeat content below 5% and signs of repeat-induced point mutation (RIP). Both species could be grown in liquid culture and on solid standard media and were sensitive to common fungicides such as hygromycin and fenhexamid. We successfully expressed a red fluorescent protein and hygromycin resistance in A. aurata following polyethylene glycol-mediated protoplast transformation, demonstrating that Arachnopeziza species are amenable to genetic alterations that may include gene replacement, gene modification, and gene complementation. With this work, we established a potential model system that promises to sidestep the need for genetic modification of powdery mildew fungi by using Arachnopeziza species as a proxy to uncover the molecular functions of powdery mildew proteins.

genomics↗

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

Long noncoding RNAs emerge from transposon-derived antisense sequences and may contribute to infection stage-specific transposon regulation in a fungal phytopathogen

The genome of the obligate biotrophic phytopathogenic barley powdery mildew fungus Blumeria hordei is inflated due to highly abundant and possibly active transposable elements (TEs). In the absence of the otherwise common repeat-induced point mutation transposon defense mechanism, noncoding RNAs could be key for regulating the activity of TEs and coding genes during the pathogenic life cycle. We performed time-course whole-transcriptome shotgun sequencing (RNA-seq) of total RNA derived from infected barley leaf epidermis at various stages of fungal pathogenesis and observed significant transcript accumulation and time point-dependent regulation of TEs in B. hordei. Using a manually curated consensus database of 344 TEs, we discovered phased small RNAs mapping to 104 consensus transposons, suggesting that RNA interference contributes significantly to their regulation. Further, we identified 5,127 long noncoding RNAs (lncRNAs) genome-wide in B. hordei, of which 823 originated from the antisense strand of a TE. Co-expression network analysis of lncRNAs, TEs, and coding genes throughout the asexual life cycle of B. hordei points at extensive positive and negative co-regulation of lncRNAs, subsets of TEs and coding genes. Our work suggests that similar to mammals and plants, fungal lncRNAs support the dynamic modulation of transcript levels, including TEs, during pivotal stages of host infection. The lncRNAs may support transcriptional diversity and plasticity amid loss of coding genes in powdery mildew fungi and may give rise to novel regulatory elements and virulence peptides, thus representing key drivers of rapid evolutionary adaptation to promote pathogenicity and overcome host defense.

plant biology↗

bioRxiv2021

A fungal plant pathogen overcomes conserved broad-spectrum disease resistance by rapid gene loss

Hosts and pathogens typically engage in a co-evolutionary arms race. This also applies to phytopathogenic powdery mildew fungi, which can rapidly overcome plant resistance and perform host jumps. Using experimental evolution, we show that the powdery mildew pathogen Blumeria hordei is capable of breaking the agriculturally important broad-spectrum resistance conditioned by barley loss-of-function mlo mutants. Partial mlo virulence of evolved B. hordei isolates is correlated with a distinctive pattern of adaptive mutations, including small-sized (8-40 kb) deletions, of which one is linked to the de novo insertion of a transposable element. Occurrence of the mutations is associated with a transcriptional induction of effector proteinencoding genes that is absent in mlo-avirulent isolates on mlo mutant plants. The detected mutational spectrum comprises the same loci in at least two independently isolated mlo-virulent isolates, indicating convergent multigenic evolution. The mutational events emerged in part early (within the first five asexual generations) during experimental evolution, likely generating a founder population in which incipient mlo virulence was later stabilized by additional events. This work highlights the rapid dynamic genome evolution of an obligate biotrophic plant pathogen with a transposon-enriched genome.

plant biology↗