Redox Control of ntcA Gene Expression in Synechocystis sp. PCC 6803. Nitrogen Availability and Electron Transport Regulate the Levels of the NtcA Protein

Abstract

In this work we have studied the influence of the cellular redox status in the expression of the Synechocystis sp. PCC 6803 ntcA gene. Two different ntcAtranscripts with different 5′ ends were detected, depending on the different dark/light or nitrogen availability conditions. Accumulation of a 0.8-kb ntcA message was light and nitrogen dependent, whereas a longer 1.2-kb ntcA transcript was neither light nor nitrogen regulated. NtcA protein levels increased concomitantly with the accumulation of the 0.8-kb ntcAtranscript. The light-dependent accumulation of the ntcAgene and the NtcA protein was sensitive to electron transport inhibitors. In addition, Glc-grown Synechocystis sp. cells showed a similar ntcA expression pattern in darkness to that observed under illumination. These data suggested that electron transport, and not light per se may regulatentcA gene expression. Primer extension analysis, together with gel mobility-shift assays, demonstrated that in vitro, the Synechocystis sp. NtcA protein specifically bound to the putative promoter region from the light/nitrogen-dependentntcA transcript but not to that from the constitutive 1.2-kb ntcA mRNA. Band-shift experiments carried out in the presence of thiol oxidizing/modifiying agents and different reducing/oxidizing conditions suggested that NtcA binding to its own promoter was under a thiol-dependent redox mechanism. Our results suggest that the cellular redox status plays a central role in the autoregulatory mechanism of the NtcA protein.

A Novel Mechanism, Linked to Cell Density, Largely Controls Cell Division in Synechocystis

“…The expression levels of ntcA were not affected by nitrogen sources, as described previously (Alfonso et al, 2001). pII and ntcA transcript levels were positively correlated (r s = 0.83; Supplemental Fig.…”

“…Synechocystis can take up and metabolize different nitrogen sources (nitrate, nitrite, ammonium, urea, and some amino acids; Quintero et al, 2000;Valladares et al, 2002;Muro-Pastor et al, 2005). Intriguingly, the control of the expression and activity of transporters and enzymes related to nitrogen metabolism is regulated by a complex network involving 2-oxoglutarate, NtcA (nitrogen control factor of cyanobacteria), PII (nitrogen regulatory protein PII), and PipX (PII-interacting protein X; Alfonso et al, 2001;Herrero et al, 2001;Llácer et al, 2010;Zhao et al, 2010;Espinosa et al, 2014;Lüddecke and Forchhammer, 2015).…”

DNA Microarray Analysis of Redox-Responsive Genes in the Genome of the Cyanobacterium Synechocystis sp. Strain PCC 6803

“…In addition to several genes reported to be redox responsive so far (3,5,10,12,19,23,28), more than 100 genes involved in various cellular functions in Synechocystis sp. strain PCC 6803 were shown to be affected by the redox state of the photosynthetic electron transport chain.…”

“…mRNA levels of several photosynthesis-related genes, such as psbA, which encodes the reaction center D1 polypeptide of photosystem II (PSII), psaE, which codes for a subunit of photosystem I (PSI), cpcBA, which encodes ␤ and ␣ subunits of phycocyanin, and rbcLS, which encodes subunits of ribulose 1,5-bisphosphate carboxylase, were shown to be affected by the redox state of the photosynthetic electron transport chain (3,4,6,21). Also, the thioredoxin gene (23), genes for fatty acid desaturases (19), some nitrogen-regulated genes (5,10,28), and heat shock genes (12) were reported to be under the control of photosynthetic electron transport. This raised the question of how many genes in the whole genome are regulated by photosynthetic electron transport.…”

Expression of furA is modulated by NtcA and strongly enhanced in heterocysts of Anabaena sp. PCC 7120

“…By binding to target sites that are located downstream of the transcription start point (tsp), NtcA can also play a role as repressor (Herrero et al, 2001;Muro-Pastor et al, 2001). It has been proposed that NtcA responds to redox changes (Jiang et al, 1997;Alfonso et al, 2001). Moreover, NtcA may coordinate iron acquisition and nitrogen metabolism by activating the expression of pkn41 and pkn42 (Cheng et al, 2006).…”