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An Inositolphosphorylceramide Synthase Is Involved in Regulation of Plant Programmed Cell Death Associated with Defense in Arabidopsis^[C],[W]

^a Center for Biosystems Research, University of Maryland Biotechnology Institute, Rockville, Maryland 20850
^b Donald Danforth Plant Science Center, St. Louis, Missouri 63132
^c Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814
^d Department of Plant Pathology, The Ohio State University, Columbus Ohio 43210
^e Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland 20850
^f Department of Biology, Williams College, Williamstown, Massachusetts 01267

² Address correspondence to xiao{at}umbi.umd.edu.

The Arabidopsis thaliana resistance gene RPW8 triggers the hypersensitive response (HR) to restrict powdery mildew infection via the salicylic acid–dependent signaling pathway. To further understand how RPW8 signaling is regulated, we have conducted a genetic screen to identify mutations enhancing RPW8-mediated HR-like cell death (designated erh). Here, we report the isolation and characterization of the Arabidopsis erh1 mutant, in which the At2g37940 locus is knocked out by a T-DNA insertion. Loss of function of ERH1 results in salicylic acid accumulation, enhanced transcription of RPW8 and RPW8-dependent spontaneous HR-like cell death in leaf tissues, and reduction in plant stature. Sequence analysis suggests that ERH1 may encode the long-sought Arabidopsis functional homolog of yeast and protozoan inositolphosphorylceramide synthase (IPCS), which converts ceramide to inositolphosphorylceramide. Indeed, ERH1 is able to rescue the yeast aur1 mutant, which lacks the IPCS, and the erh1 mutant plants display reduced (53% of wild type) levels of leaf IPCS activity, indicating that ERH1 encodes a plant IPCS. Consistent with its biochemical function, the erh1 mutation causes ceramide accumulation in plants expressing RPW8. These data reinforce the concept that sphingolipid metabolism (specifically, ceramide accumulation) plays an important role in modulating plant programmed cell death associated with defense.