Phosphoproteomics of Arabidopsis chloroplasts reveals involvement of the STN7 kinase in phosphorylation of nucleoid protein pTAC16

Abstract

a b s t r a c tLight-regulated protein kinases STN7 and STN8 phosphorylate thylakoid membrane proteins and also affect expression of several chloroplast proteins via yet unknown mechanisms. Comparative phosphoproteomics of acetic acid protein extracts of chloroplasts from Arabidopsis thaliana wild type, stn7, stn8 and stn7stn8 mutants yielded two previously unknown findings: (i) neither STN7 nor STN8 kinase was required for phosphorylation of Ser-48 in Lhcb1.1-1.3 proteins; and (ii) phosphorylation of Thr-451 in pTAC16 protein was STN7-dependent. pTAC16 was found distributed between thylakoids and nucleoid. Its knockout did not affect the nucleoid protein composition and the Thr-451 phosphorylated protein was excluded from the nucleoid. Thr-451 of pTAC16 is conserved in all studied plants and its phosphorylation may regulate membrane-anchoring functions of the nucleoid. Structured summary with protein interactions:RPOC2, RPOB, pTAC3, emb2746, RPOC1, pTAC2, pTAC12, pTAC16, pTAC5, pTAC14, RPOA, pTAC13, pTAC15 and pTAC6 colocalize by mass spectrometry studies of complexes (View interaction) PsbH, Lhcb4,1, Lhcb4,2, STN7, D1, D2, CP43, TSP9, CaS, PsaP, Alb3, PsbL, Rubisco, Unknown, Unknown, OEP6, pTAC16, PGRL1A, Unknown, Unknown and PsbQ colocalize by mass spectrometry studies of complexes (View interaction)

Stable Isotope Metabolic Labeling-based Quantitative Phosphoproteomic Analysis of Arabidopsis Mutants Reveals Ethylene-regulated Time-dependent Phosphoproteins and Putative Substrates of Constitutive Triple Response 1 Kinase

“…This finding suggests possible linkages from ethylene signaling to light harvesting. Among those CTR1 kinase-up-regulated and chloroplast-located phosphopeptides, it has been reported that phosphorylation of the T451 amino acid of PTAC16 and the S48 amino acid of LHCB1.1-1.3 (S47 of LHCB1.4 or S46 of LHCB1.5) are STN7-dependent and -independent, respectively (85). Thus, it is likely that there is more than one pathway from CTR1 kinase to chloroplast.…”

“…Chloroplast STN7 kinase, which is required for state transitions between photosystem I and photosystem II and for light adaptation, is one of the two light-regulated protein kinases (86). However, neither STN7 nor STN8 (the other light-regulated protein kinase in Arabidopsis) is required for the phosphorylation of S48, S47, or S46 on light harvesting chlorophyll A/B binding proteins 1.1-1.5 (LHCB1.1-1.5, AT1G29920/AT1G29910/AT1G29930/AT2G34430/AT2G34420) (85). Taken together, these data suggest that it is possible that the physical presence of wild-type CTR1 kinase may be required for the up-regulation of PTAC16, STN7, and LHCB protein phosphorylation upon ethylene induction.…”

“…One was a literaturebased kinase search, and the other was a GPS-based kinase search. For example, it was found that the phosphorylation of T451 of PTAC16 is STN7 kinase dependent (85). Thus, ethylene signaling from CTR1 to PTAC16 may be transduced through STN7 kinase, as the phosphorylation of T451 requires STN7 kinase activities exclusively.…”

New insights into plastid nucleoid structure and functionality

“…The recombinant TCP34 protein showed specific binding to chloroplast DNA isolated from spinach (Weber et al 2006). Very recently, it was postulated that next to MFP1 and TCP34 also the pTAC16 protein could anchor DNA to the thylakoid membranes (Ingelsson and Vener 2012;Majeran et al 2012). …”

Phosphoproteomics technologies and applications in plant biology research

“…In Arabidopsis, the thylakoid Ser/Thr protein kinase 7 (STN7) and STN8 kinases are light regulated and participate in phosphorylation of thylakoid membrane proteins and stroma proteins. Ingelsson and Vener (2012) performed a thylakoid phosphoproteomics study using Arabidopsis wild-type and the STN mutants stn7, stn8 , and stn7stn8 . The results showed that STN7 is required for the phosphorylation of pTAC16 at the Thr451, and pTAC16 was found to be distributed between thylakoids and nucleoid.…”