Cerebrosides A and C, Sphingolipid Elicitors of Hypersensitive Cell Death and Phytoalexin Accumulation in Rice Plants

Abstract

When plants interact with certain pathogens, they protect themselves by generating various chemical and physical barriers called the hypersensitive response. These barriers are induced by molecules called elicitors that are produced by pathogens. In the present study, the most active elicitors of the hypersensitive response in rice were isolated from the rice pathogenic fungus Magnaporthe grisea, and their structures were identified as cerebrosides A and C, sphingolipids that were previously isolated as inducers of cell differentiation in the fungus Schizophyllum commune. Treatment of rice leaves with cerebroside A induced the accumulation of antimicrobial compounds (phytoalexins), cell death, and increased resistance to subsequent infection by compatible pathogens. The degradation products of cerebroside A (fatty acid methyl ester, sphingoid base, and glucosyl sphingoid base) showed no elicitor activity. Hydrogenation of the 8E-double bond in the sphingoid base moiety or the 3E-double bond in the fatty acid moiety of cerebroside A did not alter the elicitor activity, whereas hydrogenation of the 4E-double bond in the sphingoid base moiety led to a 12-fold decrease in elicitor activity. Furthermore, glucocerebrosides from Gaucher's spleen consisting of (E)-4-sphingenine and cerebrosides from rice bran mainly consisting of (4E,8E)-4,8-sphingadienine and (4E,8Z)-4,8-sphingadienine showed no elicitor activity. These results indicate that the methyl group at C-9 and the 4E-double bond in the sphingoid base moiety of cerebrosides A and C are the key elements determining the elicitor activity of these compounds. This study is the first to show that sphingolipids have elicitor activity in plants.

Alpha-picolinic acid, a fungal toxin and mammal apoptosis-inducing agent, elicits hypersensitive-like response and enhances disease resistance in rice

“…For instance, syringolin A isolated from the nonhost pathogen Pseudomonas syringae pv syringae initiated wheat hypersensitive cell death and enhanced resistance to powdery mildew, and was also recognized by rice cell [19]. The fungal cerebrosides including cerebrosides B1 and C were shown to elicit the hypersensitive cell death and phytoalexin accumulation in rice plants [20]. Similarly, nonprotein amino acid, b-aminobutyric acid (BABA) which has biological effects known in animal cells, was also reported to protect Arabidopsis against the oomycete pathogen Peronospora parasitica through activation of natural defense mechanisms such as callose deposition and the formation of trailing necroses [21].…”

Glucosylceramide Synthases, a Gene Family Responsible for the Biosynthesis of Glucosphingolipids in Animals, Plants, and Fungi

“…The structural features required to induce this effect have been identified in studies with different molecular species of GlcCer from the phytopathogen Magnaporthe grisea (21,22). The identification of downstream members of this signaling cascade is a prerequisite for understanding the molecular mechanism of this plant-pathogen interaction.…”

Characterization of an Elicitor-Induced Rice WRKY Gene,OsWRKY71

“…1) Plants recognize pathogen attack through perception of pathogen-derived elicitors, such as chitin oligosaccharide and fungal cerebroside elicitors, via specific receptors, activating defense genes through intracellular signaling cascades. [1][2][3] In higher plants, transcriptional regulation of defense-related genes is considered to be central to induced disease resistance.…”