Penetration resistance represents the first level of plant defense against phytopathogenic fungi. Here, we report that the starch-deficient Arabidopsis thaliana phosphoglucomutase (pgm) mutant has impaired penetration resistance against the hemibiotrophic fungus Colletotrichum higginsianum. We could not determine any changes in leaf cutin and epicuticular wax composition or indolic glucosinolate levels, but detected complex alterations in the cell wall monosaccharide composition of pgm. Notably, other mutants deficient in starch biosynthesis (adg1) or mobilization (sex1) had similarly affected cell wall composition and penetration resistance. Glycome profiling analysis showed that both overall cell wall polysaccharide extractability and relative extractability of specific pectin and xylan epitopes were affected in pgm, suggesting extensive structural changes in pgm cell walls. Screening of mutants with alterations in content or modification of specific cell wall monosaccharides indicated an important function of pectic polymers for penetration resistance and hyphal growth of C. higginsianum during the biotrophic interaction phase. While mutants with affected pectic rhamnogalacturonan-I (mur8) were hypersusceptible, penetration frequency and morphology of fungal hyphae were impaired on pmr5 pmr6 mutants with increased pectin levels. Our results reveal a strong impact of starch metabolism on cell wall composition and suggest a link between carbohydrate availability, cell wall pectin and penetration resistance.

Fluorescent reporter proteins are widely used for the non-invasive monitoring of gene expression patterns, but dynamic measurements are hampered by the extremely high stability of GFP and homologue proteins. In this study, we used SsrA-mediated peptide tagging for the construction of unstable variants of the GFP derivative eYFP (enhanced yellow fluorescent protein) and applied those for transient gene expression analysis in the industrial platform organism Corynebacterium glutamicum.

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In the human pathogenic mold Aspergillus fumigatus, sexual identity is determined by the mating-type idiomorphs MAT1-1 and MAT1-2 residing at the MAT locus. Upon crossing of compatible partners, a heterothallic mating is executed to eventually form cleistothecia that contain recombinant ascospores. Given that the MAT1 gene products are DNA binding master regulators that govern this complex developmental process, we monitored the MAT1-driven transcriptomes of A. fumigatus by conditional overexpression of either MAT1 gene followed by RNA-seq analyses. Numerous genes related to the process of mating were found to be under transcriptional control, such as pheromone production and recognition. Substantial differences between the MAT1-1-and MAT1-2-driven transcriptomes could be detected by functional categorization of differentially expressed genes. Moreover, a significant and distinct impact on expression of genetic clusters of secondary metabolism became apparent, which could be verified on the product level. Unexpectedly, specific cross-regulation of the fumagillin/pseurotin supercluster was evident, thereby uncoupling its coregulatory characteristic. These insights imply a tight interconnection of sexual development accompanied by ascosporogenesis with secondary metabolite production of a pathogenic fungus and impose evolutionary constraints that link these two fundamental aspects of the fungal lifestyle.