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.

In vivomonoubiquitination of anaplerotic phosphoenolpyruvate carboxylase occurs at Lys624 in germinating sorghum seeds

“…The 32 P autoradiography also revealed PPCK2 and PPCK3 autophosphorylation (Supplementary Fig. S2), as previously described (Monreal et al , 2013). The overall results suggest that two different Class-1 PEPC populations might co-exist in germinating sorghum seeds (e.g.…”

Genome-wide Analysis of Phosphoenolpyruvate Carboxylase Gene Family and Their Response to Abiotic Stresses in Soybean

“…PEPC is activated by its positive effector, glucose 6-phosphate, and inhibited by its negative effectors, malate, aspartate, and glutamate, as well as phosphorylation catalyzed by a specific Ca 2+ -independent serine/threonine kinase known as PPCK (PEPC protein kinase)2, and dephosphorylation by a PP2A (protein phosphatase 2 A)1256. The control of reversible phosphorylation catalyzed by PPCK is an important mechanism that regulates the activity of PEPC57. In this reaction, phosphorylation catalyzed by PPCK changes the sensitivity of PEPC to its allosteric effectors2.…”

Phosphoenolpyruvate carboxylase (PEPC) and PEPC-kinase (PEPC-k) isoenzymes in Arabidopsis thaliana: role in control and abiotic stress conditions

“…Previously we described a drastic increase in PEPC-kinase activity and PEPC phosphorylation under salinity in leaves of the C 4 plant Sorghum bicolor (Echevarría et al 2001;García-Mauriño et al 2003;Monreal et al 2013a). However, for Arabidopsis plants, salinity increased PEPC activity (Fig.…”