Identification of two two‐component signal transduction mutants with enhanced sucrose biosynthesis in Synechococcus elongatus PCC 7942

Abstract

Metabolic engineering of the freshwater cyanobacterium Synechococcus elongatus PCC 7942 (Syn7942), synthesizing sucrose as the only compatible solute upon salt stress, has greatly improved its sucrose productivity. However, the signaling and regulatory mechanisms of this physiological process are still unknown. To know more about these aspects, a library of inactivation mutants for all 44 predicted signal transduction genes of Syn7942 was constructed. By evaluating sucrose production, two two-component signal transduction mutants Δ1125 and Δ1404, in which Synpcc7942_1125 and Synpcc7942_1404 was inactivated, respectively, were identified. They exhibited stably enhanced sucrose production, but the growth and the expression of sps encoding sucrose-phosphate synthase under salt stress were not affected, indicating that the corresponding signal transduction proteins do not regulate salt-induced sucrose synthesis by directly regulating sps expression. Moreover, the glycogen accumulation was enhanced in Δ1125 and Δ1404, and the salt stressintensified photodamage of these mutants was also found to be relieved. These results indicated that the basic cell metabolisms such as glycogen metabolism and photosynthesis of the mutants were affected by gene inactivation, which might further affect salt-induced sucrose synthesis. Further studies on gene functions and signaling pathways or networks of Synpcc7942_1125 and Synpcc7942_1404 would reveal more details about the molecular bases for the observed phenotypes of Δ1125 and Δ1404. K E Y W O R D Ssalt stress, signal transduction, sucrose biosynthesis, Synechococcus elongatus PCC 7942

Cyanobacteria as cell factories for the photosynthetic production of sucrose

“…In this context, a couple of studies have reported promising improvements in sucrose secretion rates by altering cyanobacterial two-component regulatory proteins, although the specific mechanisms remain uncertain. In a screen of all two-component regulatory factors in S. elongatus PCC 7942, Qiao and colleagues identified genes indirectly linked to sucrose productivity, glycogen accumulation, and photosynthetic activity ( Qiao et al, 2019 ). The partial deletion of ManR, a protein that plays a regulatory role in Mn 2+ uptake ( Ogawa et al, 2002 ; Yamaguchi et al, 2002 ; Zorina et al, 2016 ), increased sucrose by 60%, a complete knockout of Synpcc7942_1125 increased sucrose by 41% ( Qiao et al, 2019 ; Table 1 ).…”

“…In a screen of all two-component regulatory factors in S. elongatus PCC 7942, Qiao and colleagues identified genes indirectly linked to sucrose productivity, glycogen accumulation, and photosynthetic activity ( Qiao et al, 2019 ). The partial deletion of ManR, a protein that plays a regulatory role in Mn 2+ uptake ( Ogawa et al, 2002 ; Yamaguchi et al, 2002 ; Zorina et al, 2016 ), increased sucrose by 60%, a complete knockout of Synpcc7942_1125 increased sucrose by 41% ( Qiao et al, 2019 ; Table 1 ). In a separate study, overexpression of the two-component protein regulator of phycobilisome assembly B ( rpaB ) reproduced a growth-arrest phenotype in S. elongatus PCC 7942 ( Moronta-Barrios et al, 2013 ), and increased sucrose secretion in a cscB -expressing background ( Abramson et al, 2018 ; Table 1 ).…”

Glucosylglycerol phosphorylase, a potential novel pathway of microbial glucosylglycerol catabolism

“…The extraction and determination of intracellular compatible solutes (mainly GG) of Syn6803 were performed as previously described (Qiao et al 2019 ). The same procedure was applied to Marinobacter .…”

Freshwater Cyanobacterium Synechococcus elongatus PCC 7942 Adapts to an Environment with Salt Stress via Ion-Induced Enzymatic Balance of Compatible Solutes

“…RNA was extracted by using a MiniBEST plant RNA extraction kit (TaKaRa Bio, Shiga, Japan) and treated with DNase I (TaKaRa Bio). Reverse transcription of RNA was performed as previously described (55). Equal amounts of cDNA were used for further DNA amplification by PCR by using the primer pairs RT-sps-F/RT-sps-R and RT-rnpB-F/RT-rnpB-R (Table S2).…”