Identification of INOSITOL PHOSPHORYLCERAMIDE SYNTHASE 2 ( IPCS2 ) as a new rate‐limiting component in Arabidopsis pathogen entry control
Résumé
INOSITOL PHOSPHORYLCERAMIDE SYNTHASE 2 (IPCS2) is involved in the biosynthesis of complex sphingolipids at the trans ‐Golgi network (TGN). Here, we demonstrate a role of IPCS2 in penetration resistance against non‐adapted powdery mildew fungi. A novel ipcs2 W205 * mutant was recovered from a forward genetic screen for Arabidopsis plants with enhanced epidermal cell entry success of the non‐adapted barley fungus Blumeria graminis f. sp. hordei ( Bgh ). A yeast complementation assay and a sphingolipidomic approach revealed that the ipcs2 W205 * mutant represents a knock‐out and lacks IPCS2‐specific enzymatic activity. Further mutant analyses suggested that IPCS2‐derived glycosyl inositol phosphorylceramides (GIPCs) are required for cell entry control of non‐adapted fungal intruders. Confocal laser scanning microscopy (CLSM) studies indicated that upon pathogen attack, IPCS2 remains at the TGN to produce GIPCs, while focal accumulation of the defense cargo PENETRATION 3 (PEN3) at Bgh penetration sites was reduced in the ipcs2 W205 * mutant background. Thus, we propose a model in which sorting events at the TGN are facilitated by complex sphingolipids, regulating polar secretion of PEN3 to host‐pathogen contact sites to terminate fungal ingress.
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