Differential light-dependent phosphorylation of Ser and Thr residues regulates plant STN7 kinase
- Organism: Arabidopsis thaliana
- Instrument: TSQ vantage Thermo Scientific
STN7 kinase catalyzes the phosphorylation of the globally most common membrane proteins, the light harvesting complex II (LHCII) in plant chloroplasts. STN7 itself possesses one serine (Ser) and two threonine (Thr) phosphosites. We show that phosphorylation of the Thr residues protects STN7 against degradation in darkness, low light and red light, whereas increasing light intensity and far red illumination decrease phosphorylation and induce STN7 degradation. Ser phosphorylation, in turn, occurs under red and low intensity white light, coinciding with the client protein (LHCII) phosphorylation. Through analysis of the counteracting LHCII phosphatase mutant tap38/pph1, we show that Ser phosphorylation and activation of the STN7 kinase for subsequent LHCII phosphorylation are heavily affected by pre-illumination conditions. Transitions between the three activity states of the STN7 kinase (deactivated in darkness and far red light, activated in low and red light, inhibited in high light) are shown to modulate the phosphorylation of the STN7 Ser and Thr residues independently of each other. Such dynamic regulation of STN7 kinase phosphorylation is crucial for plant growth and environmental acclimation.
Quantification of percentage of phosphorylation of 3 distinct phosphosites of the plant kinase STN7. After separation in SDS-PAGE, identification of the band containing the kinase and in-gel digestion without phospho-enrichment, the peptide mixture has been first analyzed in DDA and the MS/MS acquired utilized to generate the SRM transitions. The identification of the peaks has been confirmed by digestion and SRM analysis of the same band in the Arabidopsis mutant lacking the kinase.
The differences in percentages have been quantified after treating the plants with different light conditions, i.e. only red light or far red light, or different intensities of white light during a night-day-night cycle.
Created on 2/18/16, 4:40 PM