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Phloem small RNAs, nutrient stress responses, and systemic mobility

MPS-Authors
http://pubman.mpdl.mpg.de/cone/persons/resource/persons97094

Buhtz,  A.
Micro- and Protein-Analysis, Department Willmitzer, Max Planck Institute of Molecular Plant Physiology, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons97422

Springer,  F.
Micro- and Protein-Analysis, Department Willmitzer, Max Planck Institute of Molecular Plant Physiology, Max Planck Society;

http://pubman.mpdl.mpg.de/cone/persons/resource/persons97221

Kehr,  J.
Micro- and Protein-Analysis, Department Willmitzer, Max Planck Institute of Molecular Plant Physiology, Max Planck Society;

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Buhtz, A., Pieritz, J., Springer, F., & Kehr, J. (2010). Phloem small RNAs, nutrient stress responses, and systemic mobility. BMC Plant Biology, 10, 64. doi:10.1186/1471-2229-10-64.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0014-2441-E
Abstract
Background: Nutrient availabilities and needs have to be tightly coordinated between organs to ensure a balance between uptake and consumption for metabolism, growth, and defense reactions. Since plants often have to grow in environments with sub-optimal nutrient availability, a fine tuning is vital. To achieve this, information has to flow cell-to-cell and over long-distance via xylem and phloem. Recently, specific miRNAs emerged as a new type of regulating molecules during stress and nutrient deficiency responses, and miR399 was suggested to be a phloem-mobile long-distance signal involved in the phosphate starvation response. Results: We used miRNA microarrays containing all known plant miRNAs and a set of unknown small (s) RNAs earlier cloned from Brassica phloem sap [1], to comprehensively analyze the phloem response to nutrient deficiency by removing sulfate, copper or iron, respectively, from the growth medium. We show that phloem sap contains a specific set of sRNAs that is distinct from leaves and roots, and that the phloem also responds specifically to stress. Upon S and Cu deficiencies phloem sap reacts with an increase of the same miRNAs that were earlier characterized in other tissues, while no clear positive response to -Fe was observed. However, -Fe led to a reduction of Cu- and P-responsive miRNAs. We further demonstrate that under nutrient starvation miR399 and miR395 can be translocated through graft unions from wild type scions to rootstocks of the miRNA processing hen1-1 mutant. In contrast, miR171 was not transported. Translocation of miR395 led to a down-regulation of one of its targets in rootstocks, suggesting that this transport is of functional relevance, and that miR395, in addition to the well characterized miR399, could potentially act as a long-distance information transmitter. Conclusions: Phloem sap contains a specific set of sRNAs, of which some specifically accumulate in response to nutrient deprivation. From the observation that miR395 and miR399 are phloem-mobile in grafting experiments we conclude that translocatable miRNAs might be candidates for information-transmitting molecules, but that grafting experiments alone are not sufficient to convincingly assign a signaling function.