Consequences of state transitions on the structural and functional organization of P hotosystem I in the green alga C hlamydomonas reinhardtii
Summary State transitions represent a photoacclimation process that regulates the light‐driven photosynthetic reactions in response to changes in light quality/quantity. It balances the excitation between photosystem I ( PSI ) and II ( PSII ) by shuttling LHCII , the main light‐harvesting complex of...
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Published in | The Plant journal : for cell and molecular biology Vol. 78; no. 2; pp. 181 - 191 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
01.04.2014
|
Online Access | Get full text |
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Summary: | Summary
State transitions represent a photoacclimation process that regulates the light‐driven photosynthetic reactions in response to changes in light quality/quantity. It balances the excitation between photosystem I (
PSI
) and
II
(
PSII
) by shuttling
LHCII
, the main light‐harvesting complex of green algae and plants, between them. This process is particularly important in
C
hlamydomonas reinhardtii
in which it is suggested to induce a large reorganization in the thylakoid membrane. Phosphorylation has been shown to be necessary for state transitions and the
LHCII
kinase has been identified. However, the consequences of state transitions on the structural organization and the functionality of the photosystems have not yet been elucidated. This situation is mainly because the purification of the supercomplexes has proved to be particularly difficult, thus preventing structural and functional studies. Here, we have purified and analysed
PSI
and
PSII
supercomplexes of
C
. reinhardtii
in states 1 and 2, and have studied them using biochemical, spectroscopic and structural methods. It is shown that
PSI
in state 2 is able to bind two
LHCII
trimers that contain all four
LHCII
types, and one monomer, most likely
CP
29, in addition to its nine Lhcas. This structure is the largest
PSI
complex ever observed, having an antenna size of 340
C
hls/P700. Moreover, all
PSI
‐bound Lhcs are efficient in transferring energy to
PSI
. A projection map at 20 Å resolution reveals the structural organization of the complex. Surprisingly, only
LHCII
type I,
II
and
IV
are phosphorylated when associated with
PSI
, while LHCII type III and CP29 are not, but
CP
29 is phosphorylated when associated with
PSII
in state2. |
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ISSN: | 0960-7412 1365-313X |
DOI: | 10.1111/tpj.12459 |