LAUSR

During low light- (LL) induced state transitions in dark adapted rice (Oryza sativa) leaves, light-harvesting complex (LHC) IIs become phosphorylated and associate with PSI complexes to form LHCII-PSI-LHCI supercomplexes (SCs). When the leaves were subsequently transferred to high light (HL) condition, phosphorylated LHCIIs complexes are no longer phosphorylated. Under the HL-induced transition in LHC phosphorylation status, we observed a new green band in the stacking gel of native green-PAGE, which was determined to be LHCII aggregates by immunoblotting and 77K chlorophyll fluorescence analysis. Knock-out mutants of protein phosphatase 1 (PPH1) which dephosphorylates LHCIIs failed to form these LHCII aggregates. In addition, the ability to develop non-photochemical quenching in the PPH1 mutant under HL was less than for wild-type plants. As determined by immunoblotting analysis, LHCII proteins present in LHCII-PSI-LHCI SCs included the Lhcb1 and Lhcb2 proteins. In this study, we provide evidence suggesting that LHCIIs in the LHCII-PSI-LHCI SCs are dephosphorylated and subsequently form aggregates to dissipate excess light energy under HL conditions. We propose that this LHCII aggregation, involving LHCII L-trimers, is a newly observed photoprotective light-quenching process operating in the early stage of HL acclimation in rice plants.