1 Role of the Synechococcus PCC 7942 nitrogen regulator protein PipX on NtcA controlled processes

ABSTRACT 1 The Synechococcus sp. PCC 7942 nitrogen regulator PipX interacts in a 2-oxoglutarate 2 dependent manner with the global nitrogen transcription factor NtcA and the signal 3 transduction protein PII. In vivo, PipX is involved in the NtcA-dependent induction of 4 glnB and glnN genes. To further investigate the extent to which PipX is involved in 5 global nitrogen control, the effect of pipX inactivation on various nitrogen regulated 6 processes was determined. The PipX deficient mutant was able to use nitrate as a 7 nitrogen source and to efficiently inhibit the nitrate transport upon ammonium addition 8 but showed reduced nitrate and nitrite reductase activities and a delay in the induction of 9 nitrate utilization after transfer of cultures from ammoniun to nitrate containing media. 10 In contrast to the wild-type, glutamine synthetase activity was not upregulated upon 11 depletion of combined-nitrogen from cultures of the mutant strain. Inactivation of pipX 12 impaired induction of nblA and delayed phycobilisome degradation, but did not affect 13 recovery of nitrogen-deprived cultures. Taken together, the results obtained in this work 14 indicate that PipX interacts with NtcA to facilitate efficient acclimation of 15 cyanobacteria to conditions of nitrogen limitation. 1