Small RNAs Establish Delays and Temporal Thresholds in Gene Expression

TL;DR

This study reveals how small non-coding RNAs, specifically IsrR, regulate gene expression timing in cyanobacteria, creating delays and thresholds that help distinguish between short-term and sustained stress signals.

Contribution

The paper demonstrates the role of IsrR in establishing delays and temporal thresholds in gene expression, combining mathematical modeling and experimental validation.

Findings

IsrR causes a delay in isiA mRNA accumulation.

IsrR ensures rapid decline of isiA after stress removal.

The system discriminates between transient and sustained stimuli.

Abstract

Non-coding RNAs are crucial regulators of gene expression in prokaryotes and eukaryotes, but it remains poorly understood how they affect the dynamics of transcriptional networks. We analyzed the temporal characteristics of the cyanobacterial iron stress response by mathematical modeling and quantitative experimental analyses, and focused on the role of a recently discovered small non-coding RNA, IsrR. We found that IsrR is responsible for a pronounced delay in the accumulation of isiA mRNA encoding the late-phase stress protein, IsiA, and that it ensures a rapid decline in isiA levels once external stress triggers are removed. These kinetic properties allow the system to selectively respond to sustained (as opposed to transient) stimuli, and thus establish a temporal threshold, which prevents energetically costly IsiA accumulation under short-term stress conditions. Biological information is frequently encoded in the quantitative aspects of intracellular signals (e.g., amplitude and duration). Our simulations reveal that competitive inhibition and regulated degradation allow intracellular regulatory networks to efficiently discriminate between transient and sustained inputs.