Cooperative and Independent Functionality of tmRNA and SmpB in : A Multifunctional Exploration Beyond Ribosome Rescue.

The trans-translation system, mediated by transfer-messenger RNA (tmRNA, encoded by the gene) and its partner protein SmpB, helps to release ribosomes stalled on defective mRNA and targets incomplete protein products for hydrolysis. Knocking out the and genes in various pathogens leads to different phenotypic changes, indicating that they have both cooperative and independent functionalities. This study aimed to clarify the functional relationships between tmRNA and SmpB in a pathogen that poses threats in aquaculture and human health. We characterized the expression dynamics of the and genes at different growth stages of the pathogen, assessed the responses of deletion strains Δ and Δ to various environmental stressors and carbon source supplementations, and identified the gene-regulatory networks involving both genes by integrating transcriptomic and phenotypic analyses. Our results showed that the gene maintained stable expression throughout the bacterial growth period, while exhibited upregulated expression in response to nutrient deficiencies. Compared to the wild type, both the Δ and Δ strains exhibited attenuated resistance to most stress conditions. However, Δ independently responded to starvation, while Δ specifically showed reduced resistance to lower concentrations of Fe and higher concentrations of Na ions, as well as increased utilization of the carbon source β-Methyl-D-glucoside. The transcriptomic analysis supported these phenotypic results, demonstrating that tmRNA and SmpB cooperate under nutrient-deficient conditions but operate independently in nutrient-rich environments. Phenotypic experiments confirmed that SsrA and SmpB collaboratively regulate genes involved in siderophore synthesis and iron uptake systems in response to extracellular iron deficiency. The findings of the present study provide crucial insights into the functions of the trans-translation system and highlight new roles for tmRNA and SmpB beyond trans-translation.