Signal transduction leading to appressorium formation in germinating conidia of Magnaporthe grisea: effects of second messengers diacylglycerols, ceramides and sphingomyelin

The inhibition of appressorium formation in germinating conidiospores of Magnaporthe grisea on an inductive surface by glisoprenin A could be reversed in a competitive manner by 1,2-dioctanoylglycerol, a known activator of protein kinase C. Dioctanoylglycerol and linoleic acid methyl ester induced appressorium formation on a noninductive surface. The effect of ceramides as inducers was heavily dependent on the fatty acid in the molecule. Ceramide IIIa containing linoleic acid was a good inducer whereas others had only weak effects. Sphingomyelin, however, inhibited appressorium formation induced by 1,16-hexadecanediol and to a lesser extent after induction with 8-(4-chlorophenylthio)-adenosine-3′,5′-monophosphate. The results are in agreement with our previous findings that in appressorium formation two signal transducing pathways are involved.