Review paper
From cyanobacteria and algae to land plants: The RpaB/Ycf27 regulatory network in transition
Riediger, Matthias; Hihara, Yukako; Hess, Wolfgang R.
Perspectives in Phycology Vol. 5 No. 1 (2018), p. 13 - 25
published: Jun 1, 2018
published online: Jun 12, 2018
manuscript accepted: Feb 1, 2018
manuscript revision received: Jan 24, 2018
manuscript revision requested: Dec 21, 2017
manuscript received: Sep 21, 2017
Open Access (paper may be downloaded free of charge)
Abstract
Abstract The OmpR-type transcription factor RpaB (for regulator of phycobilisome association B), or Ycf27/Rre26, in the cyanobacterium Synechocystis sp. PCC 6803 controls the expression of genes encoding proteins related to photosystems I and II, electron transport, certain other proteins and the regulatory small RNA PsrR1, with which it forms a type-4 coherent feed forward loop in the post-transcriptional control of photosynthesis. The basis for regulation through RpaB is the HLR1 element, a bipartite binding motif that consists of two octameric repeats separated by two random nucleotides. Depending on the distance between HLR1 and the start site of transcription, RpaB can activate or repress transcription. RpaB itself is part of a two-component system with Hik33 (NblS in Synechococcus elongatus PCC 7942) and might be redox controlled by the thioredoxin system. The rpaB gene cannot be deleted, i.e., it is essential in cyanobacteria. Orthologs of rpaB are ubiquitous in cyanobacteria and exist in the chloroplast genomes of red algae, of Glaucophyta, Cryptophyta, Haptophyta, and Raphidophyta, and the charophyte alga Chlorokybus atmophyticus, which exhibit stunning conservation of domains and residues known to serve as elements for signaling input and functionality. However, RpaB was lost during the early evolution of land plants, raising questions as to whether it became replaced by another mechanism.
Keywords
Chlorokybus • chloroplast • cyanobacteria • evolution • photosynthetic gene expression • red algae • redox regulation • regulatory networks • sRNAs • two-component systems