Damkjær JT, Kereiche S, Johnson MP, Kovacs L, Kiss AZ, Boekema EJ, Ruban AV, Horton P, Jansson S
The photosystem II light-harvesting protein Lhcb3 affects the macrostructure of photosystem II and the rate of state transitions in Arabidopsis
The Plant Cell: 2009 21:3245-3256

The main trimeric light-harvesting complex of higher plants(LHCII) consists of three different Lhcb proteins (Lhcb1-3).We show that Arabidopsis thaliana T-DNA knockout plants lackingLhcb3 (koLhcb3) compensate for the lack of Lhcb3 by producingincreased amounts of Lhcb1 and Lhcb2. As in wild-type plants,LHCII-photosystem II (PSII) supercomplexes were present in Lhcb3knockout plants (koLhcb3), and preservation of the LHCII trimers(M trimers) indicates that the Lhcb3 in M trimers has been replacedby Lhcb1 and/or Lhcb2. However, the rotational position of theM LHCII trimer was altered, suggesting that the Lhcb3 subunitaffects the macrostructural arrangement of the LHCII antenna.The absence of Lhcb3 did not result in any significant alterationin PSII efficiency or qE type of nonphotochemical quenching,but the rate of transition from State 1 to State 2 was increasedin koLhcb3, although the final extent of state transition wasunchanged. The level of phosphorylation of LHCII was increasedin the koLhcb3 plants compared with wild-type plants in bothState 1 and State 2. The relative increase in phosphorylationupon transition from State 1 to State 2 was also significantlyhigher in koLhcb3. It is suggested that the main function ofLhcb3 is to modulate the rate of state transitions.

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