One strategy for enhancing photosynthesis in crop plants is to improve the
ability to repair
photosystem II (PSII) in response to irreversible damage by light. D
espite the pivotal role of
thylakoid embedded FtsH protease complexes in the selective degradation of
PSII subunits during
repair, little is known about the factors involved in regulating FtsH exp
ression. Here we show using
the cyanobacterium
Synechocystis
sp. PCC 6803 that the Psb29 subunit, originally identified as a
minor component of His tagged PSII preparations, physically interacts
with FtsH complexes
in vivo
and is required for normal accumulation of the FtsH2/FtsH3 hetero oligo
meric complex involved in
PSII repair. We show using X ray crystallography that Psb29 from
Thermosynechococcus elongatus
has a unique fold consisting of a helical bundle and an extended C terminal heli
x and contains a
highly conserved region that might be involved in binding to FtsH. A similar
interaction is likely to
occur in
Arabidopsis
chloroplasts between the Psb29 homologue, termed THF1, and the
FTSH2/FTSH5 complex. The direct involvement of Psb29/THF1 in Ft
sH accumulation helps explain
why THF1 is a target during the hypersensitive response in plants induced by pathogen i
nfection.
Downregulating FtsH function and the PSII repair cycle via THF1 would cont
ribute to the production