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Phloem small RNAs, nutrient stress responses, and systemic mobility.
Anja Buhtz1, Janin Pieritz, Franziska Springer
1Centro de Biotecnología y Genómica de Plantas (UPM-INIA), Campus de Montegancedo, M40 (km38), 28223 Pozuelo de Alarcón/Madrid, Spain.
BMC Plant Biology
|April 15, 2010
Summary
Plant nutrient deficiencies trigger specific small RNA (sRNA) changes in phloem sap. Mobile microRNAs (miRNAs) like miR395 and miR399 may act as long-distance signals in plants.
Area of Science:
- Plant molecular biology
- Plant physiology
- Biochemistry
Background:
- Coordinated nutrient uptake and utilization across plant organs are essential for growth and defense.
- Plants require efficient long-distance communication via vascular tissues (xylem and phloem) to manage nutrient status, especially under deficiency.
- MicroRNAs (miRNAs) are emerging as critical regulators in plant stress and nutrient deficiency responses, with miR399 implicated in phosphate starvation signaling.
Purpose of the Study:
- To comprehensively analyze the small RNA (sRNA) profile of plant phloem sap in response to specific nutrient deficiencies (sulfate, copper, iron).
- To investigate the phloem-specific response to nutrient stress and identify mobile sRNAs.
- To determine the potential of specific miRNAs as long-distance signaling molecules in nutrient-starved plants.
Main Methods:
- Utilized miRNA microarrays to profile sRNAs in Brassica phloem sap under controlled sulfate, copper, and iron deficiencies.
- Compared phloem sRNA profiles with those from leaves and roots to identify tissue-specific responses.
- Conducted grafting experiments using wild-type and mutant (hen1-1) plants to assess miRNA translocation (miR399, miR395, miR171) through graft unions.
Main Results:
- Phloem sap harbors a distinct set of sRNAs compared to leaves and roots, with specific accumulation patterns under nutrient stress.
- Sulfate and copper deficiencies increased specific miRNAs in phloem sap, while iron deficiency showed complex effects, reducing other responsive miRNAs.
- miR399 and miR395 were translocated from scions to rootstocks in grafting experiments, with miR395 translocation leading to target gene down-regulation, suggesting functional relevance.
Conclusions:
- Phloem sap contains a unique sRNA population that responds dynamically to nutrient deprivation.
- Translocatable miRNAs, specifically miR395 and miR399, demonstrated mobility through graft unions, supporting their potential role as signaling molecules.
- While grafting experiments indicate miRNA mobility, further studies are needed to conclusively establish their function as long-distance signaling agents in nutrient response pathways.
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