Ni interferes in the Cu‐regulated transcriptional switch petJ/petE in Synechocystis sp. PCC 6803

Abstract

Plastocyanin (petE) plays an essential role in photosynthesis as an electron carrier between cytochrome b f and photosystem I, and in some cyanobacteria it can be replaced by the haem-containing protein, cytochrome c (petJ). In Synechocystis sp. PCC 6803, transcription of petE and petJ is activated and repressed, respectively, by Cu. Here, we show that Ni can act similarly to Cu in inducing petE and repressing petJ, thus leading to a partial switch between cytochrome c and plastocyanin. Transcription of these genes is only altered by Ni in Cu-depleted medium, and none of the Ni-dependent transcription factors described in Synechocystis, NrsR and InrS seem to be involved in this regulation. Finally, we show that plastocyanin is essential for growth under conditions of excess Ni.

A protease-mediated mechanism regulates the cytochromec6/ plastocyanin switch inSynechocystissp. PCC 6803

“…Expression of petJ and petE genes was analysed by Northern blot in both WT and PETR strains after copper addition to BG11C-Cu grown cells. In WT cells, petE was induced in response to copper and petJ was repressed (Figure 1a), as previously described 17,[24][25][26] . In contrast, in the PETR strain petE was expressed even in the absence of copper and petJ was not expressed in any condition (Figure 1a).…”

“…On the other hand, copM expression, which is induced in response to copper 24,37 was not detected in any condition and PC was detected even in BG11C-Cu ( Figure 1b). An increase in PC levels was still evident in the PETR strain after copper addition (Figure 1b), probably due to an increase in copper bound PC, which is more stable than apoPC 24,25 , as mRNA levels did not change after copper addition (Figure 1a). No changes were detected in CopM induction pattern ( Figure 1b).…”

“…In contrast, this system is still unknown in cyanobacteria, despite the PC/Cytc 6 switch was discovered for more than 40 years 12,13,[17][18][19][20] and frequently used for controlled expression of genes in several model systems [21][22][23] . The switch responds to the presence of copper at transcriptional level: petJ (encoding Cytc 6 ) is repressed while petE (encoding for PC) is induced 17,20,[24][25][26] . Several regulatory systems that respond to copper have been described in cyanobacteria 4 (CopRS 24,26 , InrS 25,26 , BmtR 27 ) but none of them are involved in regulating these two genes.…”

“…The switch responds to the presence of copper at transcriptional level: petJ (encoding Cytc 6 ) is repressed while petE (encoding for PC) is induced 17,20,[24][25][26] . Several regulatory systems that respond to copper have been described in cyanobacteria 4 (CopRS 24,26 , InrS 25,26 , BmtR 27 ) but none of them are involved in regulating these two genes.…”

Global proteome response ofSynechocystis6803 to extreme copper environments applied to control the activity of the induciblepetJpromoter

“…; Giner‐Lamia et al . , ) demonstrated reverse behaviour. During Cu 2+ excess, PC was strongly upregulated, and cyt c 553 was markedly downregulated.…”