AnUstilago maydisMutant Partially Blocked in P45014DMActivity Is Hypersensitive to Azole Fungicides

Fungicides and sterol-deficient mutants of Ustilago maydis: plasma membrane physico-chemical characteristics do not explain growth inhibition

“…The morphology of the sporidia was altered in similar ways when fungicide-treated cells were compared with mutants, i.e. sporidia were smaller than wild-type and swollen (A14, Tri-T) or appeared as long unseparated chains (P51, Fen-T) (data not shown) and was in accordance with previous reports (Girling, 1991 ;James et al, 1992;Keon & Hargreaves, 1996). After 52 h of culture, stationary phase had not been reached with any of the treatments or by any of the mutants (data not shown).…”

“…Moreover, a recent report on EBI-sensitive and -resistant strains of Uncinula necator showed that the extent of sterol replacement on both strains upon addition of triadimenol was very similar (Debieu et al, 1995), and basically identical results were reported for Erisiphe graminis (Senior et al, 1995). On the other hand, A14 is hypersensitive to lanosterol demethylase inhibitors, such as azole fungicides, although this step is partially blocked in this mutant (Keon & Hargreaves, 1996). Therefore, the prospect of an alternative mode of action for certain fungicides remains open.…”

“…The fungicide concentrations used in this study were carefully chosen to be non-lethal while still producing abnormal sterol accumulation comparable with that observed in the mutants (Loeffler & Hayes, 1992;James et al, 1992;Keon & Hargreaves, 1996). However, the two fungicide treatments had more profound effects as growth inhibitors than the mutations, although, as was later verified (Table 2), the effects of the fungicide treatments on the sterol composition of the plasma membranes were somewhat less than those produced by the mutations.…”

“…Hargreaves (James et al, 1992; Keon & Hargreaves, 1996) and were cultured without additions, as was the abovementioned parental strain as a control (WT).…”

The mechanism of resistance to sterol 14? demethylation inhibitors in a mutant (Erg 40) ofUstilago maydis

“…Erg 40 is a mutant of Ustilago maydis (DC) Corda generated from a wild‐type (ATCC14826) by treatment with N ‐methyl‐ N ‐nitro‐ N ‐nitrosoguanidine and selection with the polyene antibiotic amphotericin‐B 12. When grown on complex media it is a stable mutant and, unlike other similar U maydis mutants,13 is totally blocked at the 14DM step and produces only 14α methyl sterols. Its growth is half that of ATCC14826, colony morphology is different and it is resistant to DMI fungicides.…”