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Identification of a two-component signaling network implicated in organic carbon balancing in Synechococcus elongatus PCC 7942

ABSTRACT: Photosynthetic organisms need to balance the rate of photosynthesis (source activity) with the utilization of photosynthetic products by downstream reactions (sink capacity). However, cyanobacteria lack homologs to the regulatory source/sink systems well-studied in plants, making it uncertain how they sense integrated metabolic demands to coordinate upstream photosynthetic reactions to meet those energetic needs. Towards the identification of energy/sugar sensors in cyanobacteria, we utilized an engineered strain of Synechococcus elongatus PCC 7942 with a heterologous sucrose export pathway that provides an expanded and tunable metabolic sink. We conducted a comprehensive screening all two-component systems (TCS) encoded in S. elongatus by analyzing phenotypes consistent with sucrose export-induced relaxation of sink inhibition (e.g., increased photosynthetic efficiencies) in TCS knockout backgrounds. We further narrowed candidate sensor proteins by analyzing the changes observed after sucrose feeding experiments in a strain with a heterologous transporter installed, akin to classic sugar feeding experiments in plants. Taken together, we show that a clustered TCS network containing RpaA, CikB, ManS and NblS are involved in the regulation of genes related to photosynthesis, pigment synthesis, and Rubisco concentration in response to sucrose export and feeding. Analysis of the protein-protein interactome of each of these factors by proximity labeling demonstrated enrichment of enzymes involved in core metabolism and energy production. Altogether, these results highlight a regulatory TCS group that may be playing under-appreciated functions in energy balancing in photosynthetically-active cyanobacteria.

INSTRUMENT(S):

ORGANISM(S): Synechococcus Elongatus (strain Pcc 7942) (anacystis Nidulans R2)

TISSUE(S): Photosynthetic Cell

SUBMITTER: María Santos-Merino

LAB HEAD: Daniel Ducat

PROVIDER: PXD036717 | Pride | 2026-05-29

REPOSITORIES: Pride

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			Action	DRS
	CscB-SPS-CikB-APEX2__IPTG_rep1.raw	Raw
	CscB-SPS-CikB-APEX2__IPTG_rep2.raw	Raw
	CscB-SPS-CikB-APEX2__IPTG_rep3.raw	Raw
	CscB-SPS-CikB-APEX2_vs_CscB-SPS.rar.rar	Other
	CscB-SPS-CikB-APEX2_vs_CscB-SPS_search.rar	Other

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Project description:Responses to altered source–sink balance have been characterized in many crops at the physiological level, but the underlying genetic and molecular mechanisms are largely unknown. Detailed transcriptional profiling was performed in partially defoliated and shaded tomato plants to explore the effect of reduced source-to-sink ratio on molecular changes in the remaining source leaves. Transcription profiles of the remaining leaves 48 h after partial defoliation or partial shading were compared to leaves of control plants. Common significantly altered genes in the two treatments were assumed to be related to the reduced source-to-sink ratio. Sets of major genes in the abscisic acid, ethylene and gibberellin signal-transduction pathways were downregulated by both treatments. On the other hand, genes encoding cytokinin biosynthesis were upregulated. Most genes coding for transcription factors were also downregulated, especially those related to biotic and abiotic stress responses. Perhaps the most pronounced effect of reduced source-to-sink ratio was related to genes involved in the regulation of photosynthetic activity. Numerous genes coding for light-harvesting proteins, as well as those encoding plastocyanin, ferredoxin and ferredoxin NADP+ oxidoreductase were upregulated. Direct spectrophotometric analyses showed higher maximal potential activity of photosystem I with reduced source-to-sink ratio. As expected, the increased capacity for photosynthetic activity was associated with upregulation of almost all genes coding for the Calvin–Benson cycle and those encoding ATP biosynthesis in the mitochondria. Numerous transcriptional changes were observed 48 h after reducing source-to-sink ratio. Major genes in the photosynthetic-activity pathways were upregulated, whereas those in the pathways of defense mechanisms and responses to stress were downregulated. Genes involved in leaf senescence were also downregulated, suggesting that in addition to increased photosynthetic activity, the remaining leaves undergo a process of rejuvenation.

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Identification of a two-component signaling network implicated in organic carbon balancing in Synechococcus elongatus PCC 7942

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