The Frq-Frh Complex Light-Dependently Delays Sfl1-Induced Microsclerotia Formation in .

The vascular plant pathogenic fungus has to adapt to environmental changes outside and inside its host. harbors homologs of clock genes. The molecular functions and interactions of Frequency (Frq) and Frq-interacting RNA helicase (Frh) in controlling conidia or microsclerotia development were investigated in JR2. Fungal mutant strains carrying clock gene deletions, an point mutation, or gene fusions were analyzed on transcript, protein, and phenotypic levels as well as in pathogenicity assays on tomato plants. Our results support that the Frq-Frh complex is formed and that it promotes conidiation, but also that it suppresses and therefore delays microsclerotia formation in response to light. We investigated a possible link between the negative element Frq and positive regulator Suppressor of flocculation 1 (Sfl1) in microsclerotia formation to elucidate the regulatory molecular mechanism. Both Frq and Sfl1 are mainly present during the onset of microsclerotia formation with decreasing protein levels during further development. Induction of microsclerotia formation requires Sfl1 and can be delayed at early time points in the light through the Frq-Frh complex. Gaining further molecular knowledge on development will improve control of fungal growth and Verticillium wilt disease.