Phased small RNA-mediated systemic signaling in plants

Area of Science:

• Plant pathology
• Molecular biology
• Genetics

Background:

• Systemic acquired resistance (SAR) is a plant immune response involving mobile signals.
• The precise nature of the early mobile signal in SAR has remained elusive.

Purpose of the Study:

• To identify the early mobile signal responsible for initiating Systemic Acquired Resistance (SAR) in plants.
• To elucidate the biogenesis and function of novel signaling molecules in plant immunity.

Main Methods:

• Analysis of TAS3a transcript processing and tasi-RNA generation following pathogen infection.
• Investigating the role of tasi-RNAs and Auxin response factors (ARFs) in SAR induction using genetic mutants.
• Tracking the mobility of signaling molecules within plant tissues.

Main Results:

• Two phased 21-nucleotide tasi-RNAs derived from TAS3a are synthesized within 3 hours of pathogen infection, acting as the early mobile SAR signal.
• These tasi-RNAs (D7 and D8) cleave ARF2, ARF3, and ARF4, inducing SAR, while ARF3 overexpression represses SAR.
• TAS3a knockout or impaired RNA silencing compromises SAR, and both tasi-ARFs and 367-nt TAS3a transcripts are mobile via plasmodesmata.

Conclusions:

• Trans-acting small interfering RNAs (tasi-ARFs) originating from TAS3a are the primary early mobile signals that trigger Systemic Acquired Resistance.
• The tasi-ARF-ARF regulatory pathway is critical for SAR induction and plant defense against secondary infections.