Rubredoxin 1 Is Required for Formation of the Functional Photosystem II Core Complex in Arabidopsis thaliana

Abstract

Chloroplast thylakoid protein rubredoxin 1 (RBD1) in Chlamydomonas and its cyanobacterial homolog RubA contain a rubredoxin domain. These proteins have been proposed to participate in the assembly of photosystem II (PSII) at early stages. However, the effects of inactivation of RBD1 on PSII assembly in higher plants are largely unclear. Here, we characterized an Arabidopsis rbd1 mutant in detail. A drastic reduction of intact PSII complex but relatively higher levels of assembly intermediates including PSII RC, pre-CP47, and pre-CP43 were found in rbd1. Polysome association and ribosome profiling revealed that ribosome recruitment of psbA mRNA is specifically reduced. Consistently, in vivo protein pulse-chase labeling showed that the rate of D1/pD1 synthesis is significantly reduced in rbd1 compared with WT. Moreover, newly synthesized mature D1 and pD1/D2 can assemble into the PSII reaction center (RC) complex but further formation of larger PSII complexes is nearly totally blocked in rbd1. Our data imply that RBD1 is not only required for the formation of a functional PSII core complex during the early stages of PSII assembly but may also be involved in the translation of D1 in higher plants.

New Structural and Mechanistic Insights Into Functional Roles of Cytochrome b559 in Photosystem II

“…A conserved thylakoid membrane-bound rubredoxin (RBD1 in photosynthetic eukaryotes and RubA in cyanobacteria) is required for PSII biogenesis in diverse oxygenic photoautotrophs (Calderon et al, 2013 ; García-Cerdán et al, 2019 ; Kiss et al, 2019 ; Che et al, 2022 ). RubA-deficient mutant strains of Synechocystis were unable to maintain photoautotrophic growth under fluctuating light and showed severe defects in assembly of the heterodimeric D1/D2 reaction center complex (Kiss et al, 2019 ).…”

Rubredoxin 1 promotes the proper folding of D1 and is not required for heme b559 assembly in Chlamydomonas photosystem II

“…These data are consistent with the results obtained with the cyanobacterial mutant lacking the RBD1 ortholog RubA ( 9 ), in which the ΔrubA mutant was found to synthesize PSII subunits at close to WT levels. RBD1 is also necessary for PSII accumulation in Arabidopsis ( 6 , 10 ). Recently, a reduction in D1 synthesis was reported in the Arabidopsis rbd1 mutant ( 10 ).…”

“…In Chlamydomonas , RBD1 appears to have roles both in assembly of PSII intermediate complexes and in photoprotection during PSII assembly and repair ( 8 ). An Arabidopsis rbd1 mutant was recently shown to have reduced synthesis of the D1 subunit of PSII, leading to a model in which RBD1 might be required for the full translation of the psbA transcript encoding D1 ( 10 ). However, further elucidation of the specific role of RBD1 has been limited by our inability to isolate and study PSII that assembles in the absence of RBD1 because of the low accumulation of PSII subunits and complexes in rbd1 mutants.…”

OHP2 is not required for psbA translation in Chlamydomonas

“…Moreover, Calderon et al (2022) propose a model in which RBD1 promotes the proper folding of D1, possibly via delivery or reduction of the non-heme iron during PSII assembly. Besides a function in the early steps of PSII assembly, RBD1 from Arabidopsis was additionally proposed to play a role in the translation of the psbA mRNA (Che et al, 2022). Chl insertion into nascent D1 is not only required during PSII biogenesis, but also during repair after photoinhibition.…”