| Summary: | <p>Abstract</p> <p>Background</p> <p>Many eukaryotes, including plants and fungi make spores that resist severe environmental stress. The micro-organism <it>Dictyostelium</it> contains a single phospholipase C gene (PLC); deletion of the gene has no effect on growth, cell movement and differentiation. In this report we show that PLC is essential to sense the environment of food-activated spores.</p> <p>Results</p> <p><it>Plc</it>-null spores germinate at alkaline pH, reduced temperature or increased osmolarity, conditions at which the emerging amoebae can not grow. In contrast, food-activated wild-type spores return to dormancy till conditions in the environment allow growth. The analysis of inositol 1,4,5-trisphosphate (IP<sub>3</sub>) levels and the effect of added IP<sub>3</sub> uncover an unexpected mechanism how PLC regulates spore germination: i) deletion of PLC induces the enhanced activity of an IP<sub>5</sub> phosphatase leading to high IP<sub>3</sub> levels in <it>plc</it>-null cells; ii) in wild-type spores unfavourable conditions inhibit PLC leading to a reduction of IP<sub>3</sub> levels; addition of exogenous IP<sub>3</sub> to wild-type spores induces germination at unfavourable conditions; iii) in <it>plc</it>-null spores IP<sub>3</sub> levels remain high, also at unfavourable environmental conditions.</p> <p>Conclusions</p> <p>The results imply that environmental conditions regulate PLC activity and that IP<sub>3</sub> induces spore germination; the uncontrolled germination of <it>plc</it>-null spores is not due to a lack of PLC activity but to the constitutive activation of an alternative IP<sub>3</sub>-forming pathway.</p>
|
|---|