Factors involved in the rise of phosphoenolpyruvate carboxylase-kinase activity caused by salinity in sorghum leaves
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ORIGINAL ARTICLE
Factors involved in the rise of phosphoenolpyruvate carboxylase-kinase activity caused by salinity in sorghum leaves Jose´ A. Monreal • Cirenia Arias-Baldrich • Francisco Pe´rez-Montan˜o • Jacinto Gandullo Cristina Echevarrı´a • Sofı´a Garcı´a-Maurin˜o
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Received: 17 July 2012 / Accepted: 1 February 2013 / Published online: 14 February 2013 Ó Springer-Verlag Berlin Heidelberg 2013
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 C4PEPCase-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
Electronic supplementary material The online version of this article (doi:10.1007/s00425-013-1855-7) contains supplementary material, which is available to authorized users. J. A. Monreal C. Arias-Baldrich J. Gandullo C. Echevarrı´a S. Garcı´a-Maurin˜o (&) Departamento de Biologı´a Vegetal y Ecologı´a, Facultad de Biologı´a, Universidad de Sevilla, Avenida Reina Mercedes no 6, 41012 Seville, Spain e-mail: [email protected] F. Pe´rez-Montan˜o Departamento de Microbiologı´a, Facultad de Biologı´a, Universidad de Sevilla, Avenida Reina Mercedes no 6, 41012 Seville, Spain
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. Keywords Calcium-dependent protein kinase Phosphoenolpyruvate carboxylase Phosphoenolpyruvate carboxylase kinase Protein turnover Regulatory phosphorylation Salt stress Sorghum Ubiquitin–proteasome Abbreviations ABA Abscisic acid PI-PLC Phospho
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