Phospholipase Cdelta regulates germination of Dictyostelium spores.
BACKGROUND
Many eukaryotes, including plants and fungi make spores that resist severe environmental stress. The micro-organism Dictyostelium 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.


RESULTS
Plc-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 (IP3) levels and the effect of added IP3 uncover an unexpected mechanism how PLC regulates spore germination: i) deletion of PLC induces the enhanced activity of an IP5 phosphatase leading to high IP3 levels in plc-null cells; ii) in wild-type spores unfavourable conditions inhibit PLC leading to a reduction of IP3 levels; addition of exogenous IP3 to wild-type spores induces germination at unfavourable conditions; iii) in plc-null spores IP3 levels remain high, also at unfavourable environmental conditions.


CONCLUSIONS
The results imply that environmental conditions regulate PLC activity and that IP3 induces spore germination; the uncontrolled germination of plc-null spores is not due to a lack of PLC activity but to the constitutive activation of an alternative IP3-forming pathway.
Van Dijken
P
P
Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands. p.vandijken@id.dlo.nl
Van Haastert
P J
PJ
D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D004023:Dictyostelium / Q000201:enzymology* / Q000502:physiology*; D017353:Gene Deletion; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000502:physiology*; D007700:Kinetics; D009997:Osmotic Pressure; D054803:Phospholipase C delta; D033761:Spores, Protozoan / Q000254:growth & development; D013696:Temperature; D010738:Type C Phospholipases / Q000235:genetics / Q000502:physiology*
D007527:Isoenzymes; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D054803:Phospholipase C delta