Tlr1612 is the major repressor of cell aggregation in the light-color-dependent c-di-GMP signaling network of Thermosynechococcus vulcanus

• Published in: Scientific reports Vol. 8; no. 1; pp. 5338 - 10
• Main Authors: Enomoto, Gen, Okuda, Yukiko, Ikeuchi, Masahiko
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 28.03.2018; Nature Publishing Group
• Subjects: 13/95; 38/77; 631/326/1320; 631/326/46; 82/29; 82/83; 96/33; 96/35; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biodegradation; Biosensors; Cell aggregation; Cellulose; Cellulose synthase; Color; Color vision; Cyanobacteria; Cyanobacteria - physiology; Cyclic GMP - analogs & derivatives; Cyclic GMP - metabolism; Efficiency; Feedback inhibition; Gene Expression Regulation, Bacterial; Genomes; Glucosyltransferases - chemistry; Glucosyltransferases - metabolism; Humanities and Social Sciences; Irradiation; Lymphocytes B; Models, Biological; multidisciplinary; Photoreceptors; Physiology; Post-transcription; Proteins; Radiation; Science; Science (multidisciplinary); Signal Transduction; Thermosynechococcus vulcanus; Transcription, Genetic
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-23628-4

Cyclic diguanylate (c-di-GMP) is a bacterial second messenger involved in sessile/motile lifestyle transitions. We previously reported that c-di-GMP is a crucial inducer of cell aggregation of the cyanobacterium Thermosynechococcus vulcanus . The three cooperating cyanobacteriochrome photoreceptors (SesA/B/C) regulate cell aggregation in a light color–dependent manner by synthesizing/degrading c-di-GMP. Although a variety of c-di-GMP signaling proteins are encoded in cyanobacterial genomes, how c-di-GMP signaling networks are organized remains elusive. Here we experimentally demonstrate that the cellulose synthase Tll0007, which is essential for cell aggregation, binds c-di-GMP although the affinity is low (K d  = 63.9 ± 5.1 µM). We also show that SesA—the main trigger of cell aggregation—is subject to strict product feedback inhibition (IC50 = 1.07 ± 0.13 µM). These results suggest that SesA-produced c-di-GMP may not directly bind to Tll0007. We therefore systematically analyzed all 10 of the genes encoding proteins containing a c-di-GMP synthesis/degradation domain. We identified Tlr1612, harboring both domains, as the major repressor of cell aggregation under the repressing teal-green light irradiation. tlr1612 acts downstream of sesA and is not regulated transcriptionally by light color, suggesting that Tlr1612 may be involved in c-di-GMP amplification in the signaling cascade. Post-transcriptional control is likely crucial for the light-regulated c-di-GMP signaling.