Dissection of the Mechanisms of Growth Inhibition Resulting from Loss of the PIIProtein in the Cyanobacterium Synechococcus elongatus PCC 7942

Takayuki Sakamoto, Nobuyuki Takatani, Kintake Sonoike, Haruhiko Jimbo, Yoshitaka Nishiyama, Tatsuo Omata*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


In cyanobacteria, the PII protein (the glnB gene product) regulates a number of proteins involved in nitrogen assimilation including PipX, the coactivator of the global nitrogen regulator protein NtcA. In Synechococcus elongatus PCC 7942, construction of a PII-less mutant retaining the wild-Type pipX gene is difficult because of the toxicity of uncontrolled action of PipX and the other defect(s) resulting from the loss of PIIper se, but the nature of the PipX toxicity and the PipX-independent defect(s) remains unclear. Characterization of a PipX-less glnB mutant (PD4) in this study showed that the loss of PII increases the sensitivity of PSII to ammonium. Ammonium was shown to stimulate the formation of reactive oxygen species in the mutant cells. The ammonium-sensitive growth phenotype of PD4 was rescued by the addition of an antioxidant α-Tocopherol, confirming that photo-oxidative damage was the major cause of the growth defect. A targeted PII mutant retaining wild-Type pipX was successfully constructed from the wild-Type S. elongatus strain (SPc) in the presence of α-Tocopherol. The resulting mutant (PD1X) showed an unusual chlorophyll fluorescence profile, indicating extremely slow reduction and re-oxidation of QA, which was not observed in mutants defective in both glnB and pipX. These results showed that the aberrant action of uncontrolled PipX resulted in an impairment of the electron transport reactions in both the reducing and oxidizing sides of QA.

Original languageEnglish
Pages (from-to)721-731
Number of pages11
JournalPlant and Cell Physiology
Issue number4
Publication statusPublished - 2021 Apr 1


  • Ammonium
  • Cyanobacteria
  • Oxidative stress
  • PII
  • PipX
  • Reactive oxygen species

ASJC Scopus subject areas

  • Physiology
  • Plant Science
  • Cell Biology


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