Small One-Helix Proteins Are Essential for Photosynthesis in Arabidopsis.
The extended superfamily of chlorophylla/bbinding proteins comprises the Light-Harvesting Complex Proteins (LHCs), the Early Light-Induced Proteins (ELIPs) and the Photosystem II Subunit S (PSBS). The proteins of the ELIP family were proposed to function in photoprotection or assembly of thylakoid pigment-protein complexes and are further divided into subgroups with one to three transmembrane helices. Two small One-Helix Proteins (OHPs) are expressed constitutively in green plant tissues and their levels increase in response to light stress. In this study, we show that OHP1 and OHP2 are highly conserved in photosynthetic eukaryotes, but have probably evolved independently and have distinct functions in Arabidopsis. Mutations inOHP1orOHP2caused severe growth deficits, reduced pigmentation and disturbed thylakoid architecture. Surprisingly, the expression of OHP2 was severely reduced inohp1T-DNA insertion mutants andvice versa. In bothohp1andohp2mutants, the levels of numerous photosystem components were strongly reduced and photosynthetic electron transport was almost undetectable. Accordingly,ohp1andohp2mutants were dependent on external organic carbon sources for growth and did not produce seeds. Interestingly, the induction of ELIP1 expression and Cu/Zn superoxide dismutase activity in low light conditions indicated thatohp1mutants constantly suffer from photo-oxidative stress. Based on these data, we propose that OHP1 and OHP2 play an essential role in the assembly or stabilization of photosynthetic pigment-protein complexes, especially photosystem reaction centers, in the thylakoid membrane.
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Jochen
J
Beck
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Jens N
JN
Lohscheider
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Susanne
S
Albert
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Ulrica
U
Andersson
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Kurt W
KW
Mendgen
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Marc C
MC
Rojas-Stütz
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Iwona
I
Adamska
Plant Physiology and Biochemistry Group, Department of Biology, University of Konstanz Konstanz, Germany.
Dietmar
D
Funck
Early light-induced protein family; photoprotection; photosynthesis; phylogeny; pigment-protein complexes