The plant disease resistance gene Asc-1 prevents disruption of sphingolipid metabolism during AAL-toxin-induced programmed cell death

SD Spassieva, JE Markham*, J Hille, Stefka D. Spassieva, Jonathan E. Markham

*Corresponding author for this work

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Abstract

The nectrotrophic fungus Alternaria alternata f.sp. lycopersici infects tomato plants of the genotype asc/asc by utilizing a host-selective toxin, AAL-toxin, that kills the host cells by inducing programmed cell death. Asc-1 is homologous to genes found in most eukaryotes from yeast to humans, suggesting a conserved function. A yeast strain with deletions in the homologous genes LAG1 and LAC1 was functionally complemented by Asc-1, indicating that Asc-1 functions in an analogous manner to the yeast homologues. Examination of the yeast sphingolipids, which are almost absent in the lag1Deltalac1Delta mutant, showed that Asc-1 was able to restore the synthesis of sphingolipids. We therefore examined the biosynthesis of sphingolipids in tomato by labeling leaf discs with L-[3-H-3] serine. In the absence of AAL-toxin, there was no detectable difference in sphingolipid labeling between leaf discs from Asc/Asc or asc/asc leaves. In the presence of pathologically significant concentrations of AAL-toxin however, asc/asc leaf discs showed severely reduced labeling of sphingolipids and increased label in dihydrosphingosine (DHS) and 3-ketodihydrosphingosine (3-KDHS). Leaf discs from Asc/Asc leaves responded to AAL-toxin treatment by incorporating label into different sphingolipid species. The effects of AAL-toxin on asc/asc leaflets could be partially blocked by the simultaneous application of AAL-toxin and myriocin. Leaf discs simultaneously treated with AAL-toxin and myriocin showed no incorporation of label into sphingolipids or long-chain bases as expected. These results indicate that the presence of Asc-1 is able to relieve an AAL-toxin-induced block on sphingolipid synthesis that would otherwise lead to programmed cell death.

Original languageEnglish
Pages (from-to)561-572
Number of pages12
JournalPlant Journal
Volume32
Issue number4
DOIs
Publication statusPublished - Nov-2002

Keywords

  • AAL-toxin
  • Alternaria alternata f. sp lycopersici
  • ceramide
  • programmed cell death
  • sphinganine N-acyltransferase
  • sphingolipids
  • F-SP LYCOPERSICI
  • SACCHAROMYCES-CEREVISIAE
  • FUMONISIN B-1
  • ARABIDOPSIS-THALIANA
  • FUSARIUM-MONILIFORME
  • STRESS-RESPONSE
  • TOMATO
  • CERAMIDE
  • APOPTOSIS
  • ACCUMULATION

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