A systemic small RNA signaling system in plants.

Area of Science:

• Plant molecular biology
• RNA biology
• Plant physiology

Background:

• Systemic RNA translocation influences plant development and defense.
• Long-distance mRNA transport is known, but small RNA (siRNA, miRNA) transport remains unproven.
• Understanding small RNA movement is crucial for deciphering non-cell-autonomous regulatory pathways.

Purpose of the Study:

• To demonstrate the long-distance transport of small RNAs in the phloem.
• To identify proteins involved in small RNA trafficking within plants.
• To investigate the mechanism of systemic gene silencing mediated by small RNAs.

Main Methods:

• Phloem sap collection and small RNA analysis from various plant species.
• Bioinformatic analysis to identify potential small RNA targets.
• Heterografting experiments using plant lines with spontaneous silencing.
• Biochemical characterization of pumpkin phloem sap proteins, including CmPSRP1.
• Microinjection studies to assess protein-mediated RNA trafficking.

Main Results:

• Populations of small RNA species were identified in phloem sap, dynamically responding to environmental cues and viral infections.
• Transgene-derived small interfering RNA (siRNA) was shown to move in the phloem and induce gene silencing in distant tissues.
• A novel protein, C. maxima Phloem SMALL RNA BINDING PROTEIN1 (CmPSRP1), was identified and characterized.
• CmPSRP1 selectively binds to single-stranded 25-nucleotide RNA and mediates its cell-to-cell trafficking.

Conclusions:

• Small RNAs are mobile in the plant phloem, acting as systemic signaling molecules.
• CmPSRP1 is a key component of the protein machinery involved in small RNA trafficking and systemic silencing.
• These findings reveal a novel mechanism for long-distance regulation of plant processes.