title: Involvement of phospholipase D and phosphatidic acid in the light-dependent up-regulation of sorghum leaf phosphoenolpyruvate carboxylase-kinase.
abstract: The photosynthetic phosphoenolpyruvate carboxylase (C(4)-PEPC) is regulated by phosphorylation by a phosphoenolpyruvate carboxylase kinase (PEPC-k). In Digitaria sanguinalis mesophyll protoplasts, this light-mediated transduction cascade principally requires a phosphoinositide-specific phospholipase C (PI-PLC) and a Ca(2+)-dependent step. The present study investigates the cascade components at the higher integrated level of Sorghum bicolor leaf discs and leaves. PEPC-k up-regulation required light and photosynthetic electron transport. However, the PI-PLC inhibitor U-73122 and inhibitors of calcium release from intracellular stores only partially blocked this process. Analysis of [(32)P]phosphate-labelled phospholipids showed a light-dependent increase in phospholipase D (PLD) activity. Treatment of leaf discs with n-butanol, which decreases the formation of phosphatidic acid (PA) by PLD, led to the partial inhibition of the C(4)-PEPC phosphorylation, suggesting the participation of PLD/PA in the signalling cascade. PPCK1 gene expression was strictly light-dependent. Addition of neomycin or n-butanol decreased, and a combination of both inhibitors markedly reduced PPCK1 expression and the concomitant rise in PEPC-k activity. The calcium/calmodulin antagonist W7 blocked the light-dependent up-regulation of PEPC-k, pointing to a Ca(2+)-dependent protein kinase (CDPK) integrating both second messengers, calcium and PA, which were shown to increase the activity of sorghum CDPK.
authors.affiliation: Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Avenida Reina Mercedes no. 6, Seville, Spain.
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Monreal
authors.forename: Francisco Javier
authors.initials: FJ
authors.lastname: López-Baena
authors.forename: Jean
authors.initials: J
authors.lastname: Vidal
authors.forename: Cristina
authors.initials: C
authors.lastname: Echevarría
authors.forename: Sofía
authors.initials: S
authors.lastname: García-Mauriño
mesh_terms: D020001:1-Butanol / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000528:radiation effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D055537:Light Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D010712:Phosphatidic Acids / Q000378:metabolism*; D010730:Phosphoenolpyruvate Carboxylase / Q000378:metabolism; D054801:Phosphoinositide Phospholipase C / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects; D018515:Plant Leaves / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D045868:Sorghum / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects / Q000528:radiation effects*
chemical_list: D004791:Enzyme Inhibitors; D010712:Phosphatidic Acids; D020001:1-Butanol; D011494:Protein Kinases; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; D010739:Phospholipase D; D010730:Phosphoenolpyruvate Carboxylase
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