Roles of Close Homologues SigB and SigD in Heat and High Light Acclimation of the Cyanobacterium Synechocystis sp. PCC 6803

Abstract

Acclimation of cyanobacterium Synechocystis sp. PCC6803 to suboptimal conditions is largely dependent on adjustments of gene expression, which is highly controlled by the σ factor subunits of RNA polymerase (RNAP). The SigB and SigD σ factors are close homologues. Here we show that the sigB and sigD genes are both induced in high light and heat stresses. Comparison of transcriptomes of the control strain (CS), ΔsigB, ΔsigD, ΔsigBCE (containing SigD as the only functional group 2 σ factor), and ΔsigCDE (SigB as the only functional group 2 σ factor) strains in standard, high light, and high temperature conditions revealed that the SigB and SigD factors regulate different sets of genes and SigB and SigD regulons are highly dependent on stress conditions. The SigB regulon is bigger than the SigD regulon at high temperature, whereas, in high light, the SigD regulon is bigger than the SigB regulon. Furthermore, our results show that favoring the SigB or SigD factor by deleting other group 2 σ factors does not lead to superior acclimation to high light or high temperature, indicating that all group 2 σ factors play roles in the acclimation processes.

Site-2 Protease Slr1821 Regulates Carbon/Nitrogen Homeostasis during Ammonium Stress Acclimation in Cyanobacterium Synechocystis sp. PCC 6803

“…PerR (Slr1738) controlled the defense against metal and oxidative stress [ 57 , 58 ]. The SigD factor was upregulated in high light, heat, singlet oxygen and H 2 O 2 stresses, and was regarded as central regulator of oxidative stress acclimation [ 59 , 60 ]. SigD was also suggested to regulate the partitioning of carbon skeletons in low nitrogen, since an abnormally high glycogen content was detected in Delta sigBCE strain (SigD is active) [ 61 ].…”

Investigation of singlet oxygen sensitive genes in the cyanobacteriumSynechocystisPCC 6803

“…This finding strongly indicates that 1 O 2 is involved in the expression of sigD , which appears to be the only 1 O 2 -dependent sigma factor in Synechocystis . sigD expression has been shown to be upregulated by light (Imamura et al ., 2003), as well as by HL and heat stress (Turunen et al ., 2022), both of which can involve 1 O 2 formation (for heat-induced 1 O 2 formation see (Prasad et al ., 2016)), providing support for our finding. However, the deletion of sigD in Synechocystis did not eliminate the HL-induced upregulation of hliB , lilA, or ssr2016 (coding for a hypothetical protein) (Turunen et al ., 2022), which are among the most strongly 1 O 2 -responsive genes according to our results.…”

“…sigD expression has been shown to be upregulated by light (Imamura et al ., 2003), as well as by HL and heat stress (Turunen et al ., 2022), both of which can involve 1 O 2 formation (for heat-induced 1 O 2 formation see (Prasad et al ., 2016)), providing support for our finding. However, the deletion of sigD in Synechocystis did not eliminate the HL-induced upregulation of hliB , lilA, or ssr2016 (coding for a hypothetical protein) (Turunen et al ., 2022), which are among the most strongly 1 O 2 -responsive genes according to our results. HL-induced hliB , lilA, or ssr2016 expression was not affected by deleting sigB , sigBCE or sigCDE either (Turunen et al ., 2022), which shows that Group-2 sigma factors are unlikely to participate in 1 O 2 -dependent signaling in Synechocystis .…”

“…However, the deletion of sigD in Synechocystis did not eliminate the HL-induced upregulation of hliB , lilA, or ssr2016 (coding for a hypothetical protein) (Turunen et al ., 2022), which are among the most strongly 1 O 2 -responsive genes according to our results. HL-induced hliB , lilA, or ssr2016 expression was not affected by deleting sigB , sigBCE or sigCDE either (Turunen et al ., 2022), which shows that Group-2 sigma factors are unlikely to participate in 1 O 2 -dependent signaling in Synechocystis .…”

Engineering RNA polymerase to construct biotechnological host strains of cyanobacteria

“…Without the SigB factor, Synechocystis cells do not acclimate well to high salt stress or to osmotic stress, whereas the ΔsigCDE strain containing SigB as its only group 2 σ factor shows improved tolerance to salinity, in comparison to the control strain (Pollari et al 2008;Tyystjärvi et al 2013). SigB also plays a role in high light and oxidative stresses by activating carotenoid synthesis and reactive oxygen species (ROS) scavenging mechanisms (Pollari et al 2009;Hakkila et al 2013Hakkila et al , 2014Hakkila et al , 2019Turunen et al 2022).…”