A putative phospholipase C is involved in Pichia fermentans dimorphic transition

Background: Pichia fermentans DiSAABA 726 is a dimorphic yeast that reversibly shifts from yeast-like to
pseudohyphal morphology. This yeast behaves as a promising antagonist of Monilia spp. in the yeast-like form,
but becomes a destructive plant pathogen in the pseudohyphal form thus raising the problem of the biological
risk associated with the use of dimorphic yeasts as microbial antagonists in the biocontrol of phytopathogenic
fungi.
Methods: Pichia fermentans DiSAABA 726 was grown in urea- and methionine-containing media in order to induce
and separate yeast-like and pseudohyphal morphologies. Total RNA was extracted from yeast-like cells
and pseudohyphae and retro-transcribed into cDNA. A rapid subtraction hybridization approach was utilized
to obtain the cDNA sequences putatively over-expressed during growth on methionine-containing medium
and involved in pseudohyphal transition.
Results: Five genes that are over-expressed during yeast-like/pseudohyphal dimorphic transition were isolated.
One of these, encoding a putative phospholipase C, is involved in P. fermentans filamentation. In fact, while the
inhibition of phospholipase C, by means of 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphorylcholine (Et-
18), is accompanied by a significant reduction of pseudohyphae formation in P. fermentans, the addition of exogenous
cAMP fully restores pseudohyphal growth also in the presence of Et-18.
Conclusion: Phospholipase C is part of a putative “methionine sensing machinery” that activates cAMP-PKA signal
transduction pathway and controls P. fermentans yeast-like/pseudohyphal dimorphic transition.
General significance: Phospholipase C is a promising molecular target for further investigations into the link between
pseudohyphae formation and pathogenicity in P. fermentans.