Septation of Infectious Hyphae Is Critical for Appressoria Formation and Virulence in the Smut Fungus Ustilago Maydis

Differentiation of hyphae into specialized infection structures, known as appressoria, is a common feature of plant pathogenic fungi that penetrate the plant cuticle. Appressorium formation in U. maydis is triggered by environmental signals but the molecular mechanism of this hyphal differentiation is largely unknown. Infectious hyphae grow on the leaf surface by inserting regularly spaced retraction septa at the distal end of the tip cell leaving empty sections of collapsed hyphae behind. Here we show that formation of retraction septa is critical for appressorium formation and virulence in U. maydis. We demonstrate that the diaphanous-related formin Drf1 is necessary for actomyosin ring formation during septation of infectious hyphae. Drf1 acts as an effector of a Cdc42 GTPase signaling module, which also consists of the Cdc42-specific guanine nucleotide exchange factor Don1 and the Ste20-like kinase Don3. Deletion of drf1, don1 or don3 abolished formation of retraction septa resulting in reduced virulence. Appressorium formation in these mutants was not completely blocked but infection structures were found only at the tip of short filaments indicating that retraction septa are necessary for appressorium formation in extended infectious hyphae. In addition, appressoria of drf1 mutants penetrated the plant tissue less frequently

Button battery induced cellular damage: a pathophysiological study

Button batteries (BB) are frequently swallowed and must be removed immediately as, if they remain in the esophagus, they can cause severe damage with fatal prognosis. To better understand the molecular mechanism of esophagus damage, we performed a study aimed to analyze heat production, pH variation, electrical work and metal release from BB incubated in cell culture media. Cytotoxicity and apoptosis induced in a human monocytes cell line (U937) was also investigated.Calculated transferred heat was around 244 J with a maximal increase of temperature of 7.26 K/g medium whose pH, reflecting medium electrolysis, was 12.2 after about 2 h incubation. Release of metals also occurred. Only 49.7 ± 1.9% of U937 monocytes remained viable after 90 min of incubation in DMEM containing BB. Those results suggest that BB discharge induce cytotoxicity and tissue injury probably due to multiple combinations of at least thermic, caustic and toxic phenomena. As maximal effects occurred in less than 2 h, they prompt for fast removal of battery from esophagus. Keywords: Button battery, Electrolysis, Calorimetry, Heat transfer, Metal ions, pH, Cytotoxicity, Apoptosi