Stimulation of sexual reproduction in Phytophthora cactorum by phospholipids is not due to sterol contamination

Abstract

Phytophthora cadorum did not form oospores on basal medium unless phosphatidylcholine (lecithin) or phosphatidylethanolamine (cephalin) was added. After removal of putative sterols by aminopropyl column chromatography, the activities of lecithin and cephalin were increased 47-and 2*8-fold, respectively, thus confirming the previous reports that sterols are not essential for sexual reproduction in this organism. Thin-layer chromatography (TLC) of the commercial lecithin revealed the presence of an unknown inhibitory substance which, when added to the purified lecithin, caused a 50% reduction of oospore formation. Commercial cephalin also showed a twofold increase in activity after removal of putative sterols and the existence of an unknown inhibitor when it was subjected to TLC. Addition of the inhibitor to the purified cephalin completely inhibited the growth of the test organism. One sample of lecithin tested was not stimulatory to oospore formation. However, after washing with deionized water or NaCl solution, it induced the production of 17300 and 24450 oospores (100 pg)-', respectively. The ability of cephalin to induce oospore formation was increased 2.3-fold by washing with deionized water and 8-3-fold by washing with NaCl solution. Like sterols, the digitonin precipitable component (digitonide) of the non-phospholipid fraction of commercial lecithin or cephalin was stimulatory to oospore formation of P. cactorum but not Phytophthora parasitica. However, the non-digitonide component was not only more active than the digitonide component, but also stimulatory to P. parasitica. Gas chromatography and mass spectrometry (GC-MS) analysis of the digitonide component from lecithin failed to detect any putative sterol contaminant. The amount of the putative sterol contaminant in the digitonide component from cephalin was also below the detection limit of GC-MS. When 001-10 ng cholesterol was added to basal medium discs each containing 100 pg cephalin, the numbers of oospores produced by P. cactorum and P. parasitica were not significantly changed. It is concluded that, in the fungi tested, sterols did not play any significant role in the stimulation of sexual reproduction by highly purified phospholipids.

Are elicitins cryptograms in plant-Oomycete communications?

“…But a lack of sterol supply never affects the fungal growth of P. cactorum [M. Ponchet et al, unpublished data]. Stimulation of reproduction organ formation could be obtained by bringing phospholipids to P. cactorum [154,155] or to Pythium aphanidermatum [156], even with synthetic compounds [M. Ponchet et al, unpublished data]. This later result excludes that the biological activity of phospholipids results from their contamination by sterols, in contrast to previous conclusions [157].…”

Chemotaxis and oospore formation in Phytophthora sojae are controlled by G‐protein‐coupled receptors with a phosphatidylinositol phosphate kinase domain

“…Results from previous Phytophthora studies showed the stimulatory effect of lipids on the production of oospores. In Phytophthora cactorum , basal medium supplemented with phosphatidylcholine (PtdCho) enhanced oospore formation (Ko, ; Jee et al ., 1997; 2002). To examine the effect of PtdCho on sexual development of PsGK5 ‐silenced transformants, T2, T8, WT and CK were grown on Plich's medium containing 0, 2 or 4 mg ml −1 PtdCho respectively.…”

“…plemented with phosphatidylcholine (PtdCho) enhanced oospore formation (Ko, 1988;Jee et al, 1997;. To examine the effect of PtdCho on sexual development of PsGK5-silenced transformants, T2, T8, WT and CK were grown on Plich's medium containing 0, 2 or 4 mg ml -1 PtdCho respectively.…”

The devastating oomycete phytopathogen Phytophthora cactorum: Insights into its biology and molecular features

“…Additionally, the accumulated sterol functions to regulate the life cycle of P. cactorum (Nes & Stafford, 1983 ). However, it was subsequently found that sterols are stimulatory but not essential to sexual reproduction in P. cactorum (Jee et al, 1997 ; Ko, 1985 ; Ko & Ho, 1983 ). Sexual oospores can overwinter and survive in the soil for years, even without host presence.…”