A single small RNA shapes multiple symbiotic traits in rhizobia

Area of Science:

• Microbiology
• Molecular Biology
• Plant-Bacterial Interactions

Background:

• Bacterial small non-coding RNAs (sRNAs) are crucial regulators in microbial systems.
• The nitrogen-fixing root-nodule symbiosis between Rhizobium and legumes is vital for nitrogen cycling.
• The sRNA NfeR1 is the only known rhizobial regulator with broad symbiotic influence in Sinorhizobium meliloti.

Purpose of the Study:

• To identify and characterize the RNA targets of NfeR1 under nitrogen-stressed conditions.
• To elucidate the regulatory mechanisms and functional impact of NfeR1 in S. meliloti symbiosis.
• To understand the role of NfeR1 in coordinating nitrogen signaling and symbiotic performance.

Main Methods:

• MS2 affinity purification coupled with RNA sequencing (MAPS) to profile NfeR1 targets.
• Validation of NfeR1 targets and analysis of their regulatory outcomes.
• Investigation of NfeR1's role in cell cycle control, nitrogen metabolism, and nodulation gene expression.

Main Results:

• NfeR1 targets numerous mRNAs and sRNAs through anti-Shine-Dalgarno motifs, primarily causing downregulation.
• NfeR1 regulates cell morphology and DNA replication by controlling cell cycle mRNAs.
• NfeR1 represses gdhA, impacting nitrogen assimilation and promoting nodulation genes, involving a feedback loop with SmelC549.

Conclusions:

• NfeR1 functions as a central regulatory hub in a complex RNA network within S. meliloti.
• NfeR1 is critical for coordinating nitrogen (N) signaling and symbiotic performance in the Rhizobium-legume interaction.
• The study reveals a novel RNA-based regulatory mechanism influencing bacterial symbiosis.