AUTHOR=Beck Jochen , Lohscheider Jens N. , Albert Susanne , Andersson Ulrica , Mendgen Kurt W. , Rojas-Stütz Marc C. , Adamska Iwona , Funck Dietmar 

TITLE=Small One-Helix Proteins Are Essential for Photosynthesis in Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00007

DOI=10.3389/fpls.2017.00007

ISSN=1664-462X

ABSTRACT=<p>The extended superfamily of chlorophyll <italic>a/b</italic> binding 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 in <italic>OHP1</italic> or <italic>OHP2</italic> caused severe growth deficits, reduced pigmentation and disturbed thylakoid architecture. Surprisingly, the expression of OHP2 was severely reduced in <italic>ohp1</italic> T-DNA insertion mutants and <italic>vice versa</italic>. In both <italic>ohp1</italic> and <italic>ohp2</italic> mutants, the levels of numerous photosystem components were strongly reduced and photosynthetic electron transport was almost undetectable. Accordingly, <italic>ohp1</italic> and <italic>ohp2</italic> mutants 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 that <italic>ohp1</italic> mutants 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.</p>