Evidence for an inositol lipid signal pathway in the yeast-mycelium transition of Ophiostoma ulmi, the Dutch elm disease fungus

A. H. Brunton, G. M. Gadd

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    Abstract

    Results presented in this paper indicate the involvement of an inositol lipid signalling system, including protein kinase C, in the yeast-mycelium transition of Ophiostoma ulmi. The exogenous supply of inositol 1,4,5-trisphosphate (Inauthor,4,5P3) induced germ tube formation in O. ulmi, maximum germ tube formation resulting at a concentration of 30 μm. The addition of Inauthor,4,5P3 10 min after initiation of Ca2+ uptake by non-growing yeast cells of O. ulmi resulted in a slight increase in Ca2+ uptake. The protein kinase C-activating phorbol ester, phorbol 12-myristate 13-acetate (PMA), also induced a significant germination response in O. ulmi and approximately 50% of the population exhibited germ tube formation after 12 h incubation in the presence of 16 nm-PMA. This indicated a possible role for protein kinase C, and therefore diacylglycerol, in the germination response. Ca2+ uptake by yeast extract-(1% w/v) induced germ tubes of O. ulmi was slower than that which occurred in PMA- or Inauthor,4,5P3-induced germ tubes under similar conditions, PMA-induced germ tubes showing the highest levels of Ca2+ uptake. The anti-calmodulin drug R24571, at 3 μm, caused almost complete suppression of a yeast extract-induced yeast-mycelium (Y-M) transition which confirmed the involvement of calmodulin in germ tube formation. The addition of 16 nm-PMA in conjunction with yeast extract had no effect on germ tube formation yet, when added with R24571, the inhibitory effect of R24571 was reversed and an almost complete Y-M transition resulted after 16 h incubation. This provided further evidence that activation of protein kinase C was required for germ tube formation in O. ulmi. Ca2+ uptake by yeast cells or during the growth of yeast extract- and PMA-induced germ tubes of O. ulmi increased markedly over the first 12 h of growth with highest Ca2+ uptake occurring in yeast extract-induced germ tubes. Ca2+ uptake by 12 h yeast cells of O. ulmi was inhibited after preincubation for 10 min with PMA suggesting either inhibition of Ca2+ influx or stimulation of Ca2+ efflux. Use of Ca2+-loaded cells showed that efflux of Ca2+ from Ca2+-loaded yeast cells of O. ulmi was similar in the absence or presence of 70 mm glucose but increased rapidly on addition of PMA to the incubation medium.

    Original languageEnglish
    Pages (from-to)484-491
    Number of pages8
    JournalMycological Research
    Volume95
    Issue number4
    DOIs
    Publication statusPublished - Apr 1991

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