Autori: Cosmin I. Sicora, Christopher M. Brown, Otilia Cheregi, Imre Vass, Douglas A. Campbell

Editorial: BBA-Bioenergetics, 1777, p.130-139, 2008.

Rezumat:

Gloeobacter violaceus PCC 7421 is a slow-growing cyanobacterium which lacks thylakoid membranes, but whose five-membered psbA gene
family encodes three isoform variants of the PsbA (D1) reaction center protein of Photosystem II. Under standard culture conditions Gloeobacter
exhibits photosystem II electron transport, but several clear modifications in the redox potential of key cofactors bound by the PsbA protein are
manifested in the flash-fluorescence characteristics. In other cyanobacteria dynamic expression of multiple psbA genes and turnover of PsbA
isoforms is critical to counter excitation stress. We found that each of Gloeobacter’s five psbA genes is expressed, with transcript abundances
spanning 4.5 orders of magnitude. psbAI (glr2322) and psbAII (glr0779), encoding identical PsbA:2 form proteins, are constitutively expressed
and dominate the psbA transcript pool under control conditions. psbAIII (gll3144) was strongly induced under photoinhibitory high irradiance
stress, thereby contributing to a large increase in the psbA transcript pool that allowed cells to maintain their PsbA protein pools and then recover
from irradiance stress, within one cellular generation. In contrast, under comparable photoinhibition provoked by UVB the cells were unable to
maintain their psbA transcript and PsbA protein pools, and showed limited subsequent recovery. psbAIV (glr1706) and psbAV (glr2656), encoding
two divergent PsbA isoforms, showed consistent trace expression but were never quantitatively significant contributors to the psbA transcript pool.
© 2007 Elsevier B.V. All rights reserved.

Cuvinte cheie: Gloeobacter; D1 protein; Light; Photosystem II; psbA gene family; UV