Phosphoenolpyruvate carboxylase (PEPC) and PEPC-kinase (PEPC-k) isoenzymes in Arabidopsis thaliana: role in control and abiotic stress conditions
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Arabidopsis ppc3 mutant has a growth-arrest phenotype and is affected in phosphate- and salt-stress responses, showing that this protein is crucial under control or stress conditions.
Phosphoenolpyruvate carboxylase (PEPC) and its dedicated kinase (PEPC-k) are ubiquitous plant proteins implicated in many physiological processes. This work investigates specific roles for the three plant-type PEPC (PTPC) and the two PEPC-k isoenzymes in Arabidopsis thaliana. The lack of any of the PEPC isoenzymes reduced growth parameters under optimal growth conditions. PEPC activity was decreased in shoots and roots of ppc2 and ppc3 mutants, respectively. Phosphate starvation increased the expression of all PTPC and PPCK genes in shoots, but only PPC3 and PPCK2 in roots. The absence of any of these two proteins was not compensated by other isoforms in roots. The effect of salt stress on PTPC and PPCK expression was modest in shoots, but PPC3 was markedly increased in roots. Interestingly, both stresses decreased root growth in each of the mutants except for ppc3. This mutant had a stressed phenotype in control conditions (reduced root growth and high level of stress molecular markers), but was unaffected in their response to high salinity. Salt stress increased PEPC activity, its phosphorylation state, and L-malate content in roots, all these responses were abolished in the ppc3 mutant. Our results highlight the importance of the PPC3 isoenzyme for the normal development of plants and for root responses to stress.
KeywordsAnaplerotic function Phosphate starvation Protein kinase Salt stress
Phosphoenolpyruvate carboxylase kinase
Plant-type phosphoenolpyruvate carboxylase
Bacterial-type phosphoenolpyruvate carboxylase
Root system architecture
We thank Prof. Hugh Nimmo and Dr. Allan James from the University of Glasgow for discussion and advice. This research was supported by Spanish Ministerio de Economía y Competitividad (AGL2012-35708) and by Junta de Andalucía (P12-FQM-489 and PAI group BIO298).
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