Light regulation of nitrate reductase by catalytic subunits of protein phosphatase 2A

• Published in: Planta 2017-10, Vol.246 (4), p.701-710
• Main Authors: Creighton, Maria T., Sanmartín, Maite, Kataya, Amr R. A., Averkina, Irina O., Heidari, Behzad, Nemie-Feyissa, Dugassa, Sánchez-Serrano, Jose J., Lillo, Cathrine
• Format: Article
• Language: English
• Subjects: Activation; Agriculture; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - radiation effects; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biomedical and Life Sciences; Catalysis; Catalytic Domain; Catalytic subunits; Darkness; Demethylation; Ecology; Forestry; Gene Knockout Techniques; Kinases; Leucine; Life Sciences; Light; Methylation; Mutants; Mutation; Nitrate reductase; Nitrate Reductase - genetics; Nitrate Reductase - metabolism; Nitrates; ORIGINAL ARTICLE; Phosphatase; Phosphoprotein phosphatase; Plant Leaves - enzymology; Plant Leaves - genetics; Plant Leaves - radiation effects; Plant Sciences; Protein phosphatase; Protein Phosphatase 2 - genetics; Protein Phosphatase 2 - metabolism; Protein Subunits
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-017-2726-4

Protein phosphatase 2A (PP2A) dephosphorylates and activates nitrate reductase (NR) in photosynthetically active tissue when plants are transferred from darkness to light. In the present work, investigation of Arabidopsis thaliana PP2A mutant lines revealed that one of the five PP2A catalytic subunit genes, e.g., C2, was of special importance for NR activation. Impairment of NR activation was, especially pronounced in the c2c4 double mutant. Though weaker, NR activation was also impaired in the c2 single mutant, and c1c2 and c2c5 double mutants. On the other hand, NR activation in the c4c5 double mutant was as efficient as in WT. The c4 single mutant had low PP2A activity, whereas the c2 single mutant possessed WT levels of extractable PP2A activity. PP2A activity was low in both c2c4 and c4c5. Differences in extracted PP2A activity among mutants did not strictly correlate with differences in NR activation, but underpinned that C2 has a special function in NR activation in vivo. The terminal leucine in PP2A catalytic subunits is generally methylated to a high degree, but regulation and impact of methylation/demethylation is barely studied. In WT and PP2A mutants, the level of unmethylated PP2A catalytic subunits decreased during 45 min of darkness, but did not change much when light was switched on. In leucine carboxyl methyl transferase1 (LCMT1) knockout plants, which possess mainly unmethylated PP2A, NR was still activated, although not fully as efficient as in WT.