title: Factors involved in the rise of phosphoenolpyruvate carboxylase-kinase activity caused by salinity in sorghum leaves.
abstract: Salinity increases phosphoenolpyruvate carboxylase kinase (PEPCase-k) activity in sorghum leaves. This work has been focused on the mechanisms responsible for this phenomenon. The light-triggered expression of SbPPCK1 gene, accountable for the photosynthetic C4-PEPCase-k, is controlled by a complex signal transduction chain involving phospholipases C and D (PLC and PLD). These two phospholipase-derived signalling pathways were functional in salinized plants. Pharmacological agents that act on PLC (U-73122, neomycin) or PLD (n-butanol) derived signals, blocked the expression of SbPPCK1, but had little effect on PEPCase-k activity. This discrepancy was further noticed when SbPPCK1-3 gene expression and PEPCase-k activity were studied in parallel. At 172 mM, the main effect of NaCl was to decrease the rate of PEPCase-k protein turnover. Meanwhile, 258 mM NaCl significantly increased both SbPPCK1 and SbPPCK2 gene expression and/or mRNA stability. The combination of these factors contributed to maintain a high PEPCase-k activity in salinity. LiCl increased calcium-dependent protein kinase (CDPK) activity in illuminated sorghum leaves while it decreased the rate of PEPCase-k degradation. The latter effect was restrained by W7, an inhibitor of CDPK activity. Recombinant PEPCase-k protein was phosphorylated in vitro by PKA. A conserved phosphorylation motif, which can be recognized by PKA and by plant CDPKs, is present in the three PEPCase-ks proteins. Thus, it is possible that a phosphorylation event could be controlling (increasing) the stability of PEPCase-k in salinity. These results propose a new mechanism of regulation of PEPCase-k levels, and highlight the relevance of the preservation of key metabolic elements during the bulk degradation of proteins, which is commonly associated to stress.
authors: Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Avenida Reina Mercedes no 6, 41012, Seville, Spain.
authors: José A
authors: JA
authors: Monreal
authors: Cirenia
authors: C
authors: Arias-Baldrich
authors: Francisco
authors: F
authors: Pérez-Montaño
authors: Jacinto
authors: J
authors: Gandullo
authors: Cristina
authors: C
authors: Echevarría
authors: Sofía
authors: S
authors: García-Mauriño
mesh_terms: D018515:Plant Leaves / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D045868:Sorghum / Q000187:drug effects* / Q000201:enzymology* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D012965:Sodium Chloride; C069767:phosphoenolpyruvate carboxylase kinase; D017346:Protein Serine-Threonine Kinases