title: Rapid accumulation and metabolism of polyphosphoinositol and its possible role in phytoalexin biosynthesis in yeast elicitor-treated Cupressus lusitanica cell cultures.
abstract: Inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] rapidly accumulates in elicited Cupressus lusitanica Mill. cultured cells by 4- to 5-fold over the control, and then it is metabolized. Correspondingly, phospholipase C (PLC) activity toward phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P(2)] is stimulated to high levels by the elicitor and then decreases whereas Ins(1,4,5)P(3) phosphatase activity declines at the beginning of elicitation and increases later. These observations indicate that elicitor-induced biosynthesis and dephosphorylation of Ins(1,4,5)P(3) occur simultaneously and that the Ins(1,4,5)P(3) level may be regulated by both PtdIns(4,5)P(2)-PLC and Ins(1,4,5)P(3) phosphatases. Studies on the properties of PLC and Ins(1,4,5)P(3) phosphatases indicate that PLC activity toward PtdIns(4,5)P(2) was optimal at a lower Ca(2+) concentration than activity toward phosphatidylinositol whereas Ins(1,4,5)P(3) phosphatase activity is inhibited by high Ca(2+) concentration. This suggests that Ins(1,4,5)P(3) biosynthesis and degradation may be regulated by free cytosolic Ca(2+). In addition, a relationship between Ins(1,4,5)P(3) signaling and accumulation of a phytoalexin (beta-thujaplicin) is suggested because inhibition or promotion of Ins(1,4,5)P(3) accumulation by neomycin or LiCl affects elicitor-induced production of beta-thujaplicin. Moreover, ruthenium red inhibits elicitor-induced accumulation of beta-thujaplicin while thapsigargin alone induces beta-thujaplicin accumulation. These results suggest that Ca(2+) released from intracellular calcium stores may mediate elicitor-induced accumulation of beta-thujaplicin via an Ins(1,4,5)P(3) signaling pathway, since it is widely accepted that Ins(1,4,5)P(3) can mobilize Ca(2+) from intracellular stores. This work demonstrates an elicitor-triggered Ins(1,4,5)P(3) turnover, defines its enzymatic basis and regulation, and suggests a role for Ins(1,4,5)P(3) in elicitor-induced phytoalexin accumulation via a Ca(2+) signaling pathway.
authors.affiliation: Laboratory of Forest Biochemistry, Faculty of Agriculture, Kyushu University, 812-8581 Fukuoka, Japan. jianzhao@ksu.edu
authors.forename: Jian
authors.initials: J
authors.lastname: Zhao
authors.forename: YingQing
authors.initials: Y
authors.lastname: Guo
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kosaihira
authors.forename: Kokki
authors.initials: K
authors.lastname: Sakai
mesh_terms: D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D029781:Cupressus / Q000737:chemistry / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D039821:Monoterpenes / Q000378:metabolism; D009355:Neomycin / Q000494:pharmacology; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry / Q000378:metabolism*; D010936:Plant Extracts / Q000096:biosynthesis; D012717:Sesquiterpenes; D015398:Signal Transduction; D013729:Terpenes; D014334:Tropolone / Q000031:analogs & derivatives* / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism; D015003:Yeasts / Q000502:physiology; D000094162:Phytoalexins
chemical_list: D039821:Monoterpenes; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010936:Plant Extracts; D012717:Sesquiterpenes; D013729:Terpenes; D014334:Tropolone; D015544:Inositol 1,4,5-Trisphosphate; D010738:Type C Phospholipases; D009355:Neomycin; D002118:Calcium; C009479:beta-thujaplicin; D000094162:Phytoalexins