The [omega] Subunit of RNA Polymerase Is Essential for Thermal Acclimation of the Cyanobacterium Synechocystis Sp. PCC 6803

• Published in: PloS one 2014-11, Vol.9 (11)
• Main Authors: Gunnelius, Liisa, Kurkela, Juha, Hakkila, Kaisa, Koskinen, Satu, Parikainen, Marjaana, Tyystjärvi, Taina
• Format: Article
• Language: English
• Subjects: Photosynthesis; Proteins; RNA; RNA polymerases
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0112599

The rpoZ gene encodes the small [omega] subunit of RNA polymerase. A [DELTA]rpoZ strain of the cyanobacterium Synechocystis sp. PCC 6803 grew well in standard conditions (constant illumination at 40 [micro]mol photons m.sup.-2 s.sup.-1 ; 32°C; ambient CO.sub.2) but was heat sensitive and died at 40°C. In the control strain, 71 genes were at least two-fold up-regulated and 91 genes down-regulated after a 24-h treatment at 40°C, while in [DELTA]rpoZ 394 genes responded to heat. Only 62 of these heat-responsive genes were similarly regulated in both strains, and 80% of heat-responsive genes were unique for [DELTA]rpoZ. The RNA polymerase core and the primary [sigma] factor SigA were down-regulated in the control strain at 40°C but not in [DELTA]rpoZ. In accordance with reduced RNA polymerase content, the total RNA content of mild-heat-stress-treated cells was lower in the control strain than in [DELTA]rpoZ. Light-saturated photosynthetic activity decreased more in [DELTA]rpoZ than in the control strain upon mild heat stress. The amounts of photosystem II and rubisco decreased at 40°C in both strains while PSI and the phycobilisome antenna protein allophycocyanin remained at the same level as in standard conditions. The phycobilisome rod proteins, phycocyanins, diminished during the heat treatment in [DELTA]rpoZ but not in the control strain, and the nblA1 and nblA2 genes (encode NblA proteins required for phycobilisome degradation) were up-regulated only in [DELTA]rpoZ. Our results show that the [omega] subunit of RNAP is essential in heat stress because it is required for heat acclimation of diverse cellular processes.