Acclimation of Oxygenic Photosynthesis to Iron Starvation Is Controlled by the sRNA IsaR1

: Georg J, Kostova G, Vuorijoki L, Schon V, Kadowaki T, Huokko T, Baumgartner D, Muller M, Klahn S, Allahverdiyeva Y, Hihara Y, Futschik ME, Aro EM, Hess WR

Publisher: CELL PRESS

: 2017

: Current Biology

: CURRENT BIOLOGY

: CURR BIOL

: 27

: 10

: 1425

: 1436.e7

: 19

: 0960-9822

: 1879-0445

DOI: https://doi.org/10.1016/j.cub.2017.04.010

Oxygenic photosynthesis crucially depends on proteins that possess Fe (2+) or Fe/S complexes as co-factors or prosthetic groups. Here, we show that the small regulatory RNA (sRNA) IsaR1 (Iron-Stress-Activated RNA 1) plays a pivotal role in acclimation to low-iron conditions. The IsaR1 regulon consists of more than 15 direct targets, including Fe (2+)-containing proteins involved in photosynthetic electron transfer, detoxification of anion radicals, citrate cycle, and tetrapyrrole biogenesis. IsaR1 is essential for maintaining physiological levels of Fe/S cluster biogenesis proteins during iron deprivation. Consequently, IsaR1 affects the acclimation of the photosynthetic apparatus to iron starvation at three levels: (1) directly, via posttranscriptional repression of gene expression; (2) indirectly, via suppression of pigment; and (3) Fe/S cluster biosynthesis. Homologs of IsaR1 are widely conserved throughout the cyanobacterial phylum. We conclude that IsaR1 is a critically important riboregulator. These findings provide a new perspective for understanding the regulation of iron homeostasis in photosynthetic organisms.